Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[linux.git] / fs / btrfs / send.c

/*
 * Copyright (C) 2012 Alexander Block.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/bsearch.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/sort.h>
#include <linux/mount.h>
#include <linux/xattr.h>
#include <linux/posix_acl_xattr.h>
#include <linux/radix-tree.h>
#include <linux/vmalloc.h>
#include <linux/string.h>

#include "send.h"
#include "backref.h"
#include "hash.h"
#include "locking.h"
#include "disk-io.h"
#include "btrfs_inode.h"
#include "transaction.h"
#include "compression.h"

/*
 * A fs_path is a helper to dynamically build path names with unknown size.
 * It reallocates the internal buffer on demand.
 * It allows fast adding of path elements on the right side (normal path) and
 * fast adding to the left side (reversed path). A reversed path can also be
 * unreversed if needed.
 */
struct fs_path {
        union {
                struct {
                        char *start;
                        char *end;

                        char *buf;
                        unsigned short buf_len:15;
                        unsigned short reversed:1;
                        char inline_buf[];
                };
                /*
                 * Average path length does not exceed 200 bytes, we'll have
                 * better packing in the slab and higher chance to satisfy
                 * a allocation later during send.
                 */
                char pad[256];
        };
};
#define FS_PATH_INLINE_SIZE \
        (sizeof(struct fs_path) - offsetof(struct fs_path, inline_buf))


/* reused for each extent */
struct clone_root {
        struct btrfs_root *root;
        u64 ino;
        u64 offset;

        u64 found_refs;
};

#define SEND_CTX_MAX_NAME_CACHE_SIZE 128
#define SEND_CTX_NAME_CACHE_CLEAN_SIZE (SEND_CTX_MAX_NAME_CACHE_SIZE * 2)

struct send_ctx {
        struct file *send_filp;
        loff_t send_off;
        char *send_buf;
        u32 send_size;
        u32 send_max_size;
        u64 total_send_size;
        u64 cmd_send_size[BTRFS_SEND_C_MAX + 1];
        u64 flags;      /* 'flags' member of btrfs_ioctl_send_args is u64 */

        struct btrfs_root *send_root;
        struct btrfs_root *parent_root;
        struct clone_root *clone_roots;
        int clone_roots_cnt;

        /* current state of the compare_tree call */
        struct btrfs_path *left_path;
        struct btrfs_path *right_path;
        struct btrfs_key *cmp_key;

        /*
         * infos of the currently processed inode. In case of deleted inodes,
         * these are the values from the deleted inode.
         */
        u64 cur_ino;
        u64 cur_inode_gen;
        int cur_inode_new;
        int cur_inode_new_gen;
        int cur_inode_deleted;
        u64 cur_inode_size;
        u64 cur_inode_mode;
        u64 cur_inode_rdev;
        u64 cur_inode_last_extent;

        u64 send_progress;

        struct list_head new_refs;
        struct list_head deleted_refs;

        struct radix_tree_root name_cache;
        struct list_head name_cache_list;
        int name_cache_size;

        struct file_ra_state ra;

        char *read_buf;

        /*
         * We process inodes by their increasing order, so if before an
         * incremental send we reverse the parent/child relationship of
         * directories such that a directory with a lower inode number was
         * the parent of a directory with a higher inode number, and the one
         * becoming the new parent got renamed too, we can't rename/move the
         * directory with lower inode number when we finish processing it - we
         * must process the directory with higher inode number first, then
         * rename/move it and then rename/move the directory with lower inode
         * number. Example follows.
         *
         * Tree state when the first send was performed:
         *
         * .
         * |-- a                   (ino 257)
         *     |-- b               (ino 258)
         *         |
         *         |
         *         |-- c           (ino 259)
         *         |   |-- d       (ino 260)
         *         |
         *         |-- c2          (ino 261)
         *
         * Tree state when the second (incremental) send is performed:
         *
         * .
         * |-- a                   (ino 257)
         *     |-- b               (ino 258)
         *         |-- c2          (ino 261)
         *             |-- d2      (ino 260)
         *                 |-- cc  (ino 259)
         *
         * The sequence of steps that lead to the second state was:
         *
         * mv /a/b/c/d /a/b/c2/d2
         * mv /a/b/c /a/b/c2/d2/cc
         *
         * "c" has lower inode number, but we can't move it (2nd mv operation)
         * before we move "d", which has higher inode number.
         *
         * So we just memorize which move/rename operations must be performed
         * later when their respective parent is processed and moved/renamed.
         */

        /* Indexed by parent directory inode number. */
        struct rb_root pending_dir_moves;

        /*
         * Reverse index, indexed by the inode number of a directory that
         * is waiting for the move/rename of its immediate parent before its
         * own move/rename can be performed.
         */
        struct rb_root waiting_dir_moves;

        /*
         * A directory that is going to be rm'ed might have a child directory
         * which is in the pending directory moves index above. In this case,
         * the directory can only be removed after the move/rename of its child
         * is performed. Example:
         *
         * Parent snapshot:
         *
         * .                        (ino 256)
         * |-- a/                   (ino 257)
         *     |-- b/               (ino 258)
         *         |-- c/           (ino 259)
         *         |   |-- x/       (ino 260)
         *         |
         *         |-- y/           (ino 261)
         *
         * Send snapshot:
         *
         * .                        (ino 256)
         * |-- a/                   (ino 257)
         *     |-- b/               (ino 258)
         *         |-- YY/          (ino 261)
         *              |-- x/      (ino 260)
         *
         * Sequence of steps that lead to the send snapshot:
         * rm -f /a/b/c/foo.txt
         * mv /a/b/y /a/b/YY
         * mv /a/b/c/x /a/b/YY
         * rmdir /a/b/c
         *
         * When the child is processed, its move/rename is delayed until its
         * parent is processed (as explained above), but all other operations
         * like update utimes, chown, chgrp, etc, are performed and the paths
         * that it uses for those operations must use the orphanized name of
         * its parent (the directory we're going to rm later), so we need to
         * memorize that name.
         *
         * Indexed by the inode number of the directory to be deleted.
         */
        struct rb_root orphan_dirs;
};

struct pending_dir_move {
        struct rb_node node;
        struct list_head list;
        u64 parent_ino;
        u64 ino;
        u64 gen;
        struct list_head update_refs;
};

struct waiting_dir_move {
        struct rb_node node;
        u64 ino;
        /*
         * There might be some directory that could not be removed because it
         * was waiting for this directory inode to be moved first. Therefore
         * after this directory is moved, we can try to rmdir the ino rmdir_ino.
         */
        u64 rmdir_ino;
        bool orphanized;
};

struct orphan_dir_info {
        struct rb_node node;
        u64 ino;
        u64 gen;
};

struct name_cache_entry {
        struct list_head list;
        /*
         * radix_tree has only 32bit entries but we need to handle 64bit inums.
         * We use the lower 32bit of the 64bit inum to store it in the tree. If
         * more then one inum would fall into the same entry, we use radix_list
         * to store the additional entries. radix_list is also used to store
         * entries where two entries have the same inum but different
         * generations.
         */
        struct list_head radix_list;
        u64 ino;
        u64 gen;
        u64 parent_ino;
        u64 parent_gen;
        int ret;
        int need_later_update;
        int name_len;
        char name[];
};

static void inconsistent_snapshot_error(struct send_ctx *sctx,
                                        enum btrfs_compare_tree_result result,
                                        const char *what)
{
        const char *result_string;

        switch (result) {
        case BTRFS_COMPARE_TREE_NEW:
                result_string = "new";
                break;
        case BTRFS_COMPARE_TREE_DELETED:
                result_string = "deleted";
                break;
        case BTRFS_COMPARE_TREE_CHANGED:
                result_string = "updated";
                break;
        case BTRFS_COMPARE_TREE_SAME:
                ASSERT(0);
                result_string = "unchanged";
                break;
        default:
                ASSERT(0);
                result_string = "unexpected";
        }

        btrfs_err(sctx->send_root->fs_info,
                  "Send: inconsistent snapshot, found %s %s for inode %llu without updated inode item, send root is %llu, parent root is %llu",
                  result_string, what, sctx->cmp_key->objectid,
                  sctx->send_root->root_key.objectid,
                  (sctx->parent_root ?
                   sctx->parent_root->root_key.objectid : 0));
}

static int is_waiting_for_move(struct send_ctx *sctx, u64 ino);

static struct waiting_dir_move *
get_waiting_dir_move(struct send_ctx *sctx, u64 ino);

static int is_waiting_for_rm(struct send_ctx *sctx, u64 dir_ino);

static int need_send_hole(struct send_ctx *sctx)
{
        return (sctx->parent_root && !sctx->cur_inode_new &&
                !sctx->cur_inode_new_gen && !sctx->cur_inode_deleted &&
                S_ISREG(sctx->cur_inode_mode));
}

static void fs_path_reset(struct fs_path *p)
{
        if (p->reversed) {
                p->start = p->buf + p->buf_len - 1;
                p->end = p->start;
                *p->start = 0;
        } else {
                p->start = p->buf;
                p->end = p->start;
                *p->start = 0;
        }
}

static struct fs_path *fs_path_alloc(void)
{
        struct fs_path *p;

        p = kmalloc(sizeof(*p), GFP_KERNEL);
        if (!p)
                return NULL;
        p->reversed = 0;
        p->buf = p->inline_buf;
        p->buf_len = FS_PATH_INLINE_SIZE;
        fs_path_reset(p);
        return p;
}

static struct fs_path *fs_path_alloc_reversed(void)
{
        struct fs_path *p;

        p = fs_path_alloc();
        if (!p)
                return NULL;
        p->reversed = 1;
        fs_path_reset(p);
        return p;
}

static void fs_path_free(struct fs_path *p)
{
        if (!p)
                return;
        if (p->buf != p->inline_buf)
                kfree(p->buf);
        kfree(p);
}

static int fs_path_len(struct fs_path *p)
{
        return p->end - p->start;
}

static int fs_path_ensure_buf(struct fs_path *p, int len)
{
        char *tmp_buf;
        int path_len;
        int old_buf_len;

        len++;

        if (p->buf_len >= len)
                return 0;

        if (len > PATH_MAX) {
                WARN_ON(1);
                return -ENOMEM;
        }

        path_len = p->end - p->start;
        old_buf_len = p->buf_len;

        /*
         * First time the inline_buf does not suffice
         */
        if (p->buf == p->inline_buf) {
                tmp_buf = kmalloc(len, GFP_KERNEL);
                if (tmp_buf)
                        memcpy(tmp_buf, p->buf, old_buf_len);
        } else {
                tmp_buf = krealloc(p->buf, len, GFP_KERNEL);
        }
        if (!tmp_buf)
                return -ENOMEM;
        p->buf = tmp_buf;
        /*
         * The real size of the buffer is bigger, this will let the fast path
         * happen most of the time
         */
        p->buf_len = ksize(p->buf);

        if (p->reversed) {
                tmp_buf = p->buf + old_buf_len - path_len - 1;
                p->end = p->buf + p->buf_len - 1;
                p->start = p->end - path_len;
                memmove(p->start, tmp_buf, path_len + 1);
        } else {
                p->start = p->buf;
                p->end = p->start + path_len;
        }
        return 0;
}

static int fs_path_prepare_for_add(struct fs_path *p, int name_len,
                                   char **prepared)
{
        int ret;
        int new_len;

        new_len = p->end - p->start + name_len;
        if (p->start != p->end)
                new_len++;
        ret = fs_path_ensure_buf(p, new_len);
        if (ret < 0)
                goto out;

        if (p->reversed) {
                if (p->start != p->end)
                        *--p->start = '/';
                p->start -= name_len;
                *prepared = p->start;
        } else {
                if (p->start != p->end)
                        *p->end++ = '/';
                *prepared = p->end;
                p->end += name_len;
                *p->end = 0;
        }

out:
        return ret;
}

static int fs_path_add(struct fs_path *p, const char *name, int name_len)
{
        int ret;
        char *prepared;

        ret = fs_path_prepare_for_add(p, name_len, &prepared);
        if (ret < 0)
                goto out;
        memcpy(prepared, name, name_len);

out:
        return ret;
}

static int fs_path_add_path(struct fs_path *p, struct fs_path *p2)
{
        int ret;
        char *prepared;

        ret = fs_path_prepare_for_add(p, p2->end - p2->start, &prepared);
        if (ret < 0)
                goto out;
        memcpy(prepared, p2->start, p2->end - p2->start);

out:
        return ret;
}

static int fs_path_add_from_extent_buffer(struct fs_path *p,
                                          struct extent_buffer *eb,
                                          unsigned long off, int len)
{
        int ret;
        char *prepared;

        ret = fs_path_prepare_for_add(p, len, &prepared);
        if (ret < 0)
                goto out;

        read_extent_buffer(eb, prepared, off, len);

out:
        return ret;
}

static int fs_path_copy(struct fs_path *p, struct fs_path *from)
{
        int ret;

        p->reversed = from->reversed;
        fs_path_reset(p);

        ret = fs_path_add_path(p, from);

        return ret;
}


static void fs_path_unreverse(struct fs_path *p)
{
        char *tmp;
        int len;

        if (!p->reversed)
                return;

        tmp = p->start;
        len = p->end - p->start;
        p->start = p->buf;
        p->end = p->start + len;
        memmove(p->start, tmp, len + 1);
        p->reversed = 0;
}

static struct btrfs_path *alloc_path_for_send(void)
{
        struct btrfs_path *path;

        path = btrfs_alloc_path();
        if (!path)
                return NULL;
        path->search_commit_root = 1;
        path->skip_locking = 1;
        path->need_commit_sem = 1;
        return path;
}

static int write_buf(struct file *filp, const void *buf, u32 len, loff_t *off)
{
        int ret;
        mm_segment_t old_fs;
        u32 pos = 0;

        old_fs = get_fs();
        set_fs(KERNEL_DS);

        while (pos < len) {
                ret = vfs_write(filp, (__force const char __user *)buf + pos,
                                len - pos, off);
                /* TODO handle that correctly */
                /*if (ret == -ERESTARTSYS) {
                        continue;
                }*/
                if (ret < 0)
                        goto out;
                if (ret == 0) {
                        ret = -EIO;
                        goto out;
                }
                pos += ret;
        }

        ret = 0;

out:
        set_fs(old_fs);
        return ret;
}

static int tlv_put(struct send_ctx *sctx, u16 attr, const void *data, int len)
{
        struct btrfs_tlv_header *hdr;
        int total_len = sizeof(*hdr) + len;
        int left = sctx->send_max_size - sctx->send_size;

        if (unlikely(left < total_len))
                return -EOVERFLOW;

        hdr = (struct btrfs_tlv_header *) (sctx->send_buf + sctx->send_size);
        hdr->tlv_type = cpu_to_le16(attr);
        hdr->tlv_len = cpu_to_le16(len);
        memcpy(hdr + 1, data, len);
        sctx->send_size += total_len;

        return 0;
}

#define TLV_PUT_DEFINE_INT(bits) \
        static int tlv_put_u##bits(struct send_ctx *sctx,               \
                        u##bits attr, u##bits value)                    \
        {                                                               \
                __le##bits __tmp = cpu_to_le##bits(value);              \
                return tlv_put(sctx, attr, &__tmp, sizeof(__tmp));      \
        }

TLV_PUT_DEFINE_INT(64)

static int tlv_put_string(struct send_ctx *sctx, u16 attr,
                          const char *str, int len)
{
        if (len == -1)
                len = strlen(str);
        return tlv_put(sctx, attr, str, len);
}

static int tlv_put_uuid(struct send_ctx *sctx, u16 attr,
                        const u8 *uuid)
{
        return tlv_put(sctx, attr, uuid, BTRFS_UUID_SIZE);
}

static int tlv_put_btrfs_timespec(struct send_ctx *sctx, u16 attr,
                                  struct extent_buffer *eb,
                                  struct btrfs_timespec *ts)
{
        struct btrfs_timespec bts;
        read_extent_buffer(eb, &bts, (unsigned long)ts, sizeof(bts));
        return tlv_put(sctx, attr, &bts, sizeof(bts));
}


#define TLV_PUT(sctx, attrtype, attrlen, data) \
        do { \
                ret = tlv_put(sctx, attrtype, attrlen, data); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)

#define TLV_PUT_INT(sctx, attrtype, bits, value) \
        do { \
                ret = tlv_put_u##bits(sctx, attrtype, value); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)

#define TLV_PUT_U8(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 8, data)
#define TLV_PUT_U16(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 16, data)
#define TLV_PUT_U32(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 32, data)
#define TLV_PUT_U64(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 64, data)
#define TLV_PUT_STRING(sctx, attrtype, str, len) \
        do { \
                ret = tlv_put_string(sctx, attrtype, str, len); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)
#define TLV_PUT_PATH(sctx, attrtype, p) \
        do { \
                ret = tlv_put_string(sctx, attrtype, p->start, \
                        p->end - p->start); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while(0)
#define TLV_PUT_UUID(sctx, attrtype, uuid) \
        do { \
                ret = tlv_put_uuid(sctx, attrtype, uuid); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)
#define TLV_PUT_BTRFS_TIMESPEC(sctx, attrtype, eb, ts) \
        do { \
                ret = tlv_put_btrfs_timespec(sctx, attrtype, eb, ts); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)

static int send_header(struct send_ctx *sctx)
{
        struct btrfs_stream_header hdr;

        strcpy(hdr.magic, BTRFS_SEND_STREAM_MAGIC);
        hdr.version = cpu_to_le32(BTRFS_SEND_STREAM_VERSION);

        return write_buf(sctx->send_filp, &hdr, sizeof(hdr),
                                        &sctx->send_off);
}

/*
 * For each command/item we want to send to userspace, we call this function.
 */
static int begin_cmd(struct send_ctx *sctx, int cmd)
{
        struct btrfs_cmd_header *hdr;

        if (WARN_ON(!sctx->send_buf))
                return -EINVAL;

        BUG_ON(sctx->send_size);

        sctx->send_size += sizeof(*hdr);
        hdr = (struct btrfs_cmd_header *)sctx->send_buf;
        hdr->cmd = cpu_to_le16(cmd);

        return 0;
}

static int send_cmd(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_cmd_header *hdr;
        u32 crc;

        hdr = (struct btrfs_cmd_header *)sctx->send_buf;
        hdr->len = cpu_to_le32(sctx->send_size - sizeof(*hdr));
        hdr->crc = 0;

        crc = btrfs_crc32c(0, (unsigned char *)sctx->send_buf, sctx->send_size);
        hdr->crc = cpu_to_le32(crc);

        ret = write_buf(sctx->send_filp, sctx->send_buf, sctx->send_size,
                                        &sctx->send_off);

        sctx->total_send_size += sctx->send_size;
        sctx->cmd_send_size[le16_to_cpu(hdr->cmd)] += sctx->send_size;
        sctx->send_size = 0;

        return ret;
}

/*
 * Sends a move instruction to user space
 */
static int send_rename(struct send_ctx *sctx,
                     struct fs_path *from, struct fs_path *to)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret;

        btrfs_debug(fs_info, "send_rename %s -> %s", from->start, to->start);

        ret = begin_cmd(sctx, BTRFS_SEND_C_RENAME);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, from);
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_TO, to);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        return ret;
}

/*
 * Sends a link instruction to user space
 */
static int send_link(struct send_ctx *sctx,
                     struct fs_path *path, struct fs_path *lnk)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret;

        btrfs_debug(fs_info, "send_link %s -> %s", path->start, lnk->start);

        ret = begin_cmd(sctx, BTRFS_SEND_C_LINK);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_LINK, lnk);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        return ret;
}

/*
 * Sends an unlink instruction to user space
 */
static int send_unlink(struct send_ctx *sctx, struct fs_path *path)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret;

        btrfs_debug(fs_info, "send_unlink %s", path->start);

        ret = begin_cmd(sctx, BTRFS_SEND_C_UNLINK);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        return ret;
}

/*
 * Sends a rmdir instruction to user space
 */
static int send_rmdir(struct send_ctx *sctx, struct fs_path *path)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret;

        btrfs_debug(fs_info, "send_rmdir %s", path->start);

        ret = begin_cmd(sctx, BTRFS_SEND_C_RMDIR);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        return ret;
}

/*
 * Helper function to retrieve some fields from an inode item.
 */
static int __get_inode_info(struct btrfs_root *root, struct btrfs_path *path,
                          u64 ino, u64 *size, u64 *gen, u64 *mode, u64 *uid,
                          u64 *gid, u64 *rdev)
{
        int ret;
        struct btrfs_inode_item *ii;
        struct btrfs_key key;

        key.objectid = ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret) {
                if (ret > 0)
                        ret = -ENOENT;
                return ret;
        }

        ii = btrfs_item_ptr(path->nodes[0], path->slots[0],
                        struct btrfs_inode_item);
        if (size)
                *size = btrfs_inode_size(path->nodes[0], ii);
        if (gen)
                *gen = btrfs_inode_generation(path->nodes[0], ii);
        if (mode)
                *mode = btrfs_inode_mode(path->nodes[0], ii);
        if (uid)
                *uid = btrfs_inode_uid(path->nodes[0], ii);
        if (gid)
                *gid = btrfs_inode_gid(path->nodes[0], ii);
        if (rdev)
                *rdev = btrfs_inode_rdev(path->nodes[0], ii);

        return ret;
}

static int get_inode_info(struct btrfs_root *root,
                          u64 ino, u64 *size, u64 *gen,
                          u64 *mode, u64 *uid, u64 *gid,
                          u64 *rdev)
{
        struct btrfs_path *path;
        int ret;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;
        ret = __get_inode_info(root, path, ino, size, gen, mode, uid, gid,
                               rdev);
        btrfs_free_path(path);
        return ret;
}

typedef int (*iterate_inode_ref_t)(int num, u64 dir, int index,
                                   struct fs_path *p,
                                   void *ctx);

/*
 * Helper function to iterate the entries in ONE btrfs_inode_ref or
 * btrfs_inode_extref.
 * The iterate callback may return a non zero value to stop iteration. This can
 * be a negative value for error codes or 1 to simply stop it.
 *
 * path must point to the INODE_REF or INODE_EXTREF when called.
 */
static int iterate_inode_ref(struct btrfs_root *root, struct btrfs_path *path,
                             struct btrfs_key *found_key, int resolve,
                             iterate_inode_ref_t iterate, void *ctx)
{
        struct extent_buffer *eb = path->nodes[0];
        struct btrfs_item *item;
        struct btrfs_inode_ref *iref;
        struct btrfs_inode_extref *extref;
        struct btrfs_path *tmp_path;
        struct fs_path *p;
        u32 cur = 0;
        u32 total;
        int slot = path->slots[0];
        u32 name_len;
        char *start;
        int ret = 0;
        int num = 0;
        int index;
        u64 dir;
        unsigned long name_off;
        unsigned long elem_size;
        unsigned long ptr;

        p = fs_path_alloc_reversed();
        if (!p)
                return -ENOMEM;

        tmp_path = alloc_path_for_send();
        if (!tmp_path) {
                fs_path_free(p);
                return -ENOMEM;
        }


        if (found_key->type == BTRFS_INODE_REF_KEY) {
                ptr = (unsigned long)btrfs_item_ptr(eb, slot,
                                                    struct btrfs_inode_ref);
                item = btrfs_item_nr(slot);
                total = btrfs_item_size(eb, item);
                elem_size = sizeof(*iref);
        } else {
                ptr = btrfs_item_ptr_offset(eb, slot);
                total = btrfs_item_size_nr(eb, slot);
                elem_size = sizeof(*extref);
        }

        while (cur < total) {
                fs_path_reset(p);

                if (found_key->type == BTRFS_INODE_REF_KEY) {
                        iref = (struct btrfs_inode_ref *)(ptr + cur);
                        name_len = btrfs_inode_ref_name_len(eb, iref);
                        name_off = (unsigned long)(iref + 1);
                        index = btrfs_inode_ref_index(eb, iref);
                        dir = found_key->offset;
                } else {
                        extref = (struct btrfs_inode_extref *)(ptr + cur);
                        name_len = btrfs_inode_extref_name_len(eb, extref);
                        name_off = (unsigned long)&extref->name;
                        index = btrfs_inode_extref_index(eb, extref);
                        dir = btrfs_inode_extref_parent(eb, extref);
                }

                if (resolve) {
                        start = btrfs_ref_to_path(root, tmp_path, name_len,
                                                  name_off, eb, dir,
                                                  p->buf, p->buf_len);
                        if (IS_ERR(start)) {
                                ret = PTR_ERR(start);
                                goto out;
                        }
                        if (start < p->buf) {
                                /* overflow , try again with larger buffer */
                                ret = fs_path_ensure_buf(p,
                                                p->buf_len + p->buf - start);
                                if (ret < 0)
                                        goto out;
                                start = btrfs_ref_to_path(root, tmp_path,
                                                          name_len, name_off,
                                                          eb, dir,
                                                          p->buf, p->buf_len);
                                if (IS_ERR(start)) {
                                        ret = PTR_ERR(start);
                                        goto out;
                                }
                                BUG_ON(start < p->buf);
                        }
                        p->start = start;
                } else {
                        ret = fs_path_add_from_extent_buffer(p, eb, name_off,
                                                             name_len);
                        if (ret < 0)
                                goto out;
                }

                cur += elem_size + name_len;
                ret = iterate(num, dir, index, p, ctx);
                if (ret)
                        goto out;
                num++;
        }

out:
        btrfs_free_path(tmp_path);
        fs_path_free(p);
        return ret;
}

typedef int (*iterate_dir_item_t)(int num, struct btrfs_key *di_key,
                                  const char *name, int name_len,
                                  const char *data, int data_len,
                                  u8 type, void *ctx);

/*
 * Helper function to iterate the entries in ONE btrfs_dir_item.
 * The iterate callback may return a non zero value to stop iteration. This can
 * be a negative value for error codes or 1 to simply stop it.
 *
 * path must point to the dir item when called.
 */
static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
                            struct btrfs_key *found_key,
                            iterate_dir_item_t iterate, void *ctx)
{
        int ret = 0;
        struct extent_buffer *eb;
        struct btrfs_item *item;
        struct btrfs_dir_item *di;
        struct btrfs_key di_key;
        char *buf = NULL;
        int buf_len;
        u32 name_len;
        u32 data_len;
        u32 cur;
        u32 len;
        u32 total;
        int slot;
        int num;
        u8 type;

        /*
         * Start with a small buffer (1 page). If later we end up needing more
         * space, which can happen for xattrs on a fs with a leaf size greater
         * then the page size, attempt to increase the buffer. Typically xattr
         * values are small.
         */
        buf_len = PATH_MAX;
        buf = kmalloc(buf_len, GFP_KERNEL);
        if (!buf) {
                ret = -ENOMEM;
                goto out;
        }

        eb = path->nodes[0];
        slot = path->slots[0];
        item = btrfs_item_nr(slot);
        di = btrfs_item_ptr(eb, slot, struct btrfs_dir_item);
        cur = 0;
        len = 0;
        total = btrfs_item_size(eb, item);

        num = 0;
        while (cur < total) {
                name_len = btrfs_dir_name_len(eb, di);
                data_len = btrfs_dir_data_len(eb, di);
                type = btrfs_dir_type(eb, di);
                btrfs_dir_item_key_to_cpu(eb, di, &di_key);

                if (type == BTRFS_FT_XATTR) {
                        if (name_len > XATTR_NAME_MAX) {
                                ret = -ENAMETOOLONG;
                                goto out;
                        }
                        if (name_len + data_len >
                                        BTRFS_MAX_XATTR_SIZE(root->fs_info)) {
                                ret = -E2BIG;
                                goto out;
                        }
                } else {
                        /*
                         * Path too long
                         */
                        if (name_len + data_len > PATH_MAX) {
                                ret = -ENAMETOOLONG;
                                goto out;
                        }
                }

                if (name_len + data_len > buf_len) {
                        buf_len = name_len + data_len;
                        if (is_vmalloc_addr(buf)) {
                                vfree(buf);
                                buf = NULL;
                        } else {
                                char *tmp = krealloc(buf, buf_len,
                                                GFP_KERNEL | __GFP_NOWARN);

                                if (!tmp)
                                        kfree(buf);
                                buf = tmp;
                        }
                        if (!buf) {
                                buf = vmalloc(buf_len);
                                if (!buf) {
                                        ret = -ENOMEM;
                                        goto out;
                                }
                        }
                }

                read_extent_buffer(eb, buf, (unsigned long)(di + 1),
                                name_len + data_len);

                len = sizeof(*di) + name_len + data_len;
                di = (struct btrfs_dir_item *)((char *)di + len);
                cur += len;

                ret = iterate(num, &di_key, buf, name_len, buf + name_len,
                                data_len, type, ctx);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = 0;
                        goto out;
                }

                num++;
        }

out:
        kvfree(buf);
        return ret;
}

static int __copy_first_ref(int num, u64 dir, int index,
                            struct fs_path *p, void *ctx)
{
        int ret;
        struct fs_path *pt = ctx;

        ret = fs_path_copy(pt, p);
        if (ret < 0)
                return ret;

        /* we want the first only */
        return 1;
}

/*
 * Retrieve the first path of an inode. If an inode has more then one
 * ref/hardlink, this is ignored.
 */
static int get_inode_path(struct btrfs_root *root,
                          u64 ino, struct fs_path *path)
{
        int ret;
        struct btrfs_key key, found_key;
        struct btrfs_path *p;

        p = alloc_path_for_send();
        if (!p)
                return -ENOMEM;

        fs_path_reset(path);

        key.objectid = ino;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(root, &key, p, 1, 0);
        if (ret < 0)
                goto out;
        if (ret) {
                ret = 1;
                goto out;
        }
        btrfs_item_key_to_cpu(p->nodes[0], &found_key, p->slots[0]);
        if (found_key.objectid != ino ||
            (found_key.type != BTRFS_INODE_REF_KEY &&
             found_key.type != BTRFS_INODE_EXTREF_KEY)) {
                ret = -ENOENT;
                goto out;
        }

        ret = iterate_inode_ref(root, p, &found_key, 1,
                                __copy_first_ref, path);
        if (ret < 0)
                goto out;
        ret = 0;

out:
        btrfs_free_path(p);
        return ret;
}

struct backref_ctx {
        struct send_ctx *sctx;

        struct btrfs_path *path;
        /* number of total found references */
        u64 found;

        /*
         * used for clones found in send_root. clones found behind cur_objectid
         * and cur_offset are not considered as allowed clones.
         */
        u64 cur_objectid;
        u64 cur_offset;

        /* may be truncated in case it's the last extent in a file */
        u64 extent_len;

        /* data offset in the file extent item */
        u64 data_offset;

        /* Just to check for bugs in backref resolving */
        int found_itself;
};

static int __clone_root_cmp_bsearch(const void *key, const void *elt)
{
        u64 root = (u64)(uintptr_t)key;
        struct clone_root *cr = (struct clone_root *)elt;

        if (root < cr->root->objectid)
                return -1;
        if (root > cr->root->objectid)
                return 1;
        return 0;
}

static int __clone_root_cmp_sort(const void *e1, const void *e2)
{
        struct clone_root *cr1 = (struct clone_root *)e1;
        struct clone_root *cr2 = (struct clone_root *)e2;

        if (cr1->root->objectid < cr2->root->objectid)
                return -1;
        if (cr1->root->objectid > cr2->root->objectid)
                return 1;
        return 0;
}

/*
 * Called for every backref that is found for the current extent.
 * Results are collected in sctx->clone_roots->ino/offset/found_refs
 */
static int __iterate_backrefs(u64 ino, u64 offset, u64 root, void *ctx_)
{
        struct backref_ctx *bctx = ctx_;
        struct clone_root *found;
        int ret;
        u64 i_size;

        /* First check if the root is in the list of accepted clone sources */
        found = bsearch((void *)(uintptr_t)root, bctx->sctx->clone_roots,
                        bctx->sctx->clone_roots_cnt,
                        sizeof(struct clone_root),
                        __clone_root_cmp_bsearch);
        if (!found)
                return 0;

        if (found->root == bctx->sctx->send_root &&
            ino == bctx->cur_objectid &&
            offset == bctx->cur_offset) {
                bctx->found_itself = 1;
        }

        /*
         * There are inodes that have extents that lie behind its i_size. Don't
         * accept clones from these extents.
         */
        ret = __get_inode_info(found->root, bctx->path, ino, &i_size, NULL, NULL,
                               NULL, NULL, NULL);
        btrfs_release_path(bctx->path);
        if (ret < 0)
                return ret;

        if (offset + bctx->data_offset + bctx->extent_len > i_size)
                return 0;

        /*
         * Make sure we don't consider clones from send_root that are
         * behind the current inode/offset.
         */
        if (found->root == bctx->sctx->send_root) {
                /*
                 * TODO for the moment we don't accept clones from the inode
                 * that is currently send. We may change this when
                 * BTRFS_IOC_CLONE_RANGE supports cloning from and to the same
                 * file.
                 */
                if (ino >= bctx->cur_objectid)
                        return 0;
#if 0
                if (ino > bctx->cur_objectid)
                        return 0;
                if (offset + bctx->extent_len > bctx->cur_offset)
                        return 0;
#endif
        }

        bctx->found++;
        found->found_refs++;
        if (ino < found->ino) {
                found->ino = ino;
                found->offset = offset;
        } else if (found->ino == ino) {
                /*
                 * same extent found more then once in the same file.
                 */
                if (found->offset > offset + bctx->extent_len)
                        found->offset = offset;
        }

        return 0;
}

/*
 * Given an inode, offset and extent item, it finds a good clone for a clone
 * instruction. Returns -ENOENT when none could be found. The function makes
 * sure that the returned clone is usable at the point where sending is at the
 * moment. This means, that no clones are accepted which lie behind the current
 * inode+offset.
 *
 * path must point to the extent item when called.
 */
static int find_extent_clone(struct send_ctx *sctx,
                             struct btrfs_path *path,
                             u64 ino, u64 data_offset,
                             u64 ino_size,
                             struct clone_root **found)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret;
        int extent_type;
        u64 logical;
        u64 disk_byte;
        u64 num_bytes;
        u64 extent_item_pos;
        u64 flags = 0;
        struct btrfs_file_extent_item *fi;
        struct extent_buffer *eb = path->nodes[0];
        struct backref_ctx *backref_ctx = NULL;
        struct clone_root *cur_clone_root;
        struct btrfs_key found_key;
        struct btrfs_path *tmp_path;
        int compressed;
        u32 i;

        tmp_path = alloc_path_for_send();
        if (!tmp_path)
                return -ENOMEM;

        /* We only use this path under the commit sem */
        tmp_path->need_commit_sem = 0;

        backref_ctx = kmalloc(sizeof(*backref_ctx), GFP_KERNEL);
        if (!backref_ctx) {
                ret = -ENOMEM;
                goto out;
        }

        backref_ctx->path = tmp_path;

        if (data_offset >= ino_size) {
                /*
                 * There may be extents that lie behind the file's size.
                 * I at least had this in combination with snapshotting while
                 * writing large files.
                 */
                ret = 0;
                goto out;
        }

        fi = btrfs_item_ptr(eb, path->slots[0],
                        struct btrfs_file_extent_item);
        extent_type = btrfs_file_extent_type(eb, fi);
        if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                ret = -ENOENT;
                goto out;
        }
        compressed = btrfs_file_extent_compression(eb, fi);

        num_bytes = btrfs_file_extent_num_bytes(eb, fi);
        disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
        if (disk_byte == 0) {
                ret = -ENOENT;
                goto out;
        }
        logical = disk_byte + btrfs_file_extent_offset(eb, fi);

        down_read(&fs_info->commit_root_sem);
        ret = extent_from_logical(fs_info, disk_byte, tmp_path,
                                  &found_key, &flags);
        up_read(&fs_info->commit_root_sem);
        btrfs_release_path(tmp_path);

        if (ret < 0)
                goto out;
        if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                ret = -EIO;
                goto out;
        }

        /*
         * Setup the clone roots.
         */
        for (i = 0; i < sctx->clone_roots_cnt; i++) {
                cur_clone_root = sctx->clone_roots + i;
                cur_clone_root->ino = (u64)-1;
                cur_clone_root->offset = 0;
                cur_clone_root->found_refs = 0;
        }

        backref_ctx->sctx = sctx;
        backref_ctx->found = 0;
        backref_ctx->cur_objectid = ino;
        backref_ctx->cur_offset = data_offset;
        backref_ctx->found_itself = 0;
        backref_ctx->extent_len = num_bytes;
        /*
         * For non-compressed extents iterate_extent_inodes() gives us extent
         * offsets that already take into account the data offset, but not for
         * compressed extents, since the offset is logical and not relative to
         * the physical extent locations. We must take this into account to
         * avoid sending clone offsets that go beyond the source file's size,
         * which would result in the clone ioctl failing with -EINVAL on the
         * receiving end.
         */
        if (compressed == BTRFS_COMPRESS_NONE)
                backref_ctx->data_offset = 0;
        else
                backref_ctx->data_offset = btrfs_file_extent_offset(eb, fi);

        /*
         * The last extent of a file may be too large due to page alignment.
         * We need to adjust extent_len in this case so that the checks in
         * __iterate_backrefs work.
         */
        if (data_offset + num_bytes >= ino_size)
                backref_ctx->extent_len = ino_size - data_offset;

        /*
         * Now collect all backrefs.
         */
        if (compressed == BTRFS_COMPRESS_NONE)
                extent_item_pos = logical - found_key.objectid;
        else
                extent_item_pos = 0;
        ret = iterate_extent_inodes(fs_info, found_key.objectid,
                                    extent_item_pos, 1, __iterate_backrefs,
                                    backref_ctx);

        if (ret < 0)
                goto out;

        if (!backref_ctx->found_itself) {
                /* found a bug in backref code? */
                ret = -EIO;
                btrfs_err(fs_info,
                          "did not find backref in send_root. inode=%llu, offset=%llu, disk_byte=%llu found extent=%llu",
                          ino, data_offset, disk_byte, found_key.objectid);
                goto out;
        }

        btrfs_debug(fs_info,
                    "find_extent_clone: data_offset=%llu, ino=%llu, num_bytes=%llu, logical=%llu",
                    data_offset, ino, num_bytes, logical);

        if (!backref_ctx->found)
                btrfs_debug(fs_info, "no clones found");

        cur_clone_root = NULL;
        for (i = 0; i < sctx->clone_roots_cnt; i++) {
                if (sctx->clone_roots[i].found_refs) {
                        if (!cur_clone_root)
                                cur_clone_root = sctx->clone_roots + i;
                        else if (sctx->clone_roots[i].root == sctx->send_root)
                                /* prefer clones from send_root over others */
                                cur_clone_root = sctx->clone_roots + i;
                }

        }

        if (cur_clone_root) {
                *found = cur_clone_root;
                ret = 0;
        } else {
                ret = -ENOENT;
        }

out:
        btrfs_free_path(tmp_path);
        kfree(backref_ctx);
        return ret;
}

static int read_symlink(struct btrfs_root *root,
                        u64 ino,
                        struct fs_path *dest)
{
        int ret;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_file_extent_item *ei;
        u8 type;
        u8 compression;
        unsigned long off;
        int len;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        if (ret) {
                /*
                 * An empty symlink inode. Can happen in rare error paths when
                 * creating a symlink (transaction committed before the inode
                 * eviction handler removed the symlink inode items and a crash
                 * happened in between or the subvol was snapshoted in between).
                 * Print an informative message to dmesg/syslog so that the user
                 * can delete the symlink.
                 */
                btrfs_err(root->fs_info,
                          "Found empty symlink inode %llu at root %llu",
                          ino, root->root_key.objectid);
                ret = -EIO;
                goto out;
        }

        ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                        struct btrfs_file_extent_item);
        type = btrfs_file_extent_type(path->nodes[0], ei);
        compression = btrfs_file_extent_compression(path->nodes[0], ei);
        BUG_ON(type != BTRFS_FILE_EXTENT_INLINE);
        BUG_ON(compression);

        off = btrfs_file_extent_inline_start(ei);
        len = btrfs_file_extent_inline_len(path->nodes[0], path->slots[0], ei);

        ret = fs_path_add_from_extent_buffer(dest, path->nodes[0], off, len);

out:
        btrfs_free_path(path);
        return ret;
}

/*
 * Helper function to generate a file name that is unique in the root of
 * send_root and parent_root. This is used to generate names for orphan inodes.
 */
static int gen_unique_name(struct send_ctx *sctx,
                           u64 ino, u64 gen,
                           struct fs_path *dest)
{
        int ret = 0;
        struct btrfs_path *path;
        struct btrfs_dir_item *di;
        char tmp[64];
        int len;
        u64 idx = 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        while (1) {
                len = snprintf(tmp, sizeof(tmp), "o%llu-%llu-%llu",
                                ino, gen, idx);
                ASSERT(len < sizeof(tmp));

                di = btrfs_lookup_dir_item(NULL, sctx->send_root,
                                path, BTRFS_FIRST_FREE_OBJECTID,
                                tmp, strlen(tmp), 0);
                btrfs_release_path(path);
                if (IS_ERR(di)) {
                        ret = PTR_ERR(di);
                        goto out;
                }
                if (di) {
                        /* not unique, try again */
                        idx++;
                        continue;
                }

                if (!sctx->parent_root) {
                        /* unique */
                        ret = 0;
                        break;
                }

                di = btrfs_lookup_dir_item(NULL, sctx->parent_root,
                                path, BTRFS_FIRST_FREE_OBJECTID,
                                tmp, strlen(tmp), 0);
                btrfs_release_path(path);
                if (IS_ERR(di)) {
                        ret = PTR_ERR(di);
                        goto out;
                }
                if (di) {
                        /* not unique, try again */
                        idx++;
                        continue;
                }
                /* unique */
                break;
        }

        ret = fs_path_add(dest, tmp, strlen(tmp));

out:
        btrfs_free_path(path);
        return ret;
}

enum inode_state {
        inode_state_no_change,
        inode_state_will_create,
        inode_state_did_create,
        inode_state_will_delete,
        inode_state_did_delete,
};

static int get_cur_inode_state(struct send_ctx *sctx, u64 ino, u64 gen)
{
        int ret;
        int left_ret;
        int right_ret;
        u64 left_gen;
        u64 right_gen;

        ret = get_inode_info(sctx->send_root, ino, NULL, &left_gen, NULL, NULL,
                        NULL, NULL);
        if (ret < 0 && ret != -ENOENT)
                goto out;
        left_ret = ret;

        if (!sctx->parent_root) {
                right_ret = -ENOENT;
        } else {
                ret = get_inode_info(sctx->parent_root, ino, NULL, &right_gen,
                                NULL, NULL, NULL, NULL);
                if (ret < 0 && ret != -ENOENT)
                        goto out;
                right_ret = ret;
        }

        if (!left_ret && !right_ret) {
                if (left_gen == gen && right_gen == gen) {
                        ret = inode_state_no_change;
                } else if (left_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_create;
                        else
                                ret = inode_state_will_create;
                } else if (right_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_delete;
                        else
                                ret = inode_state_will_delete;
                } else  {
                        ret = -ENOENT;
                }
        } else if (!left_ret) {
                if (left_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_create;
                        else
                                ret = inode_state_will_create;
                } else {
                        ret = -ENOENT;
                }
        } else if (!right_ret) {
                if (right_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_delete;
                        else
                                ret = inode_state_will_delete;
                } else {
                        ret = -ENOENT;
                }
        } else {
                ret = -ENOENT;
        }

out:
        return ret;
}

static int is_inode_existent(struct send_ctx *sctx, u64 ino, u64 gen)
{
        int ret;

        ret = get_cur_inode_state(sctx, ino, gen);
        if (ret < 0)
                goto out;

        if (ret == inode_state_no_change ||
            ret == inode_state_did_create ||
            ret == inode_state_will_delete)
                ret = 1;
        else
                ret = 0;

out:
        return ret;
}

/*
 * Helper function to lookup a dir item in a dir.
 */
static int lookup_dir_item_inode(struct btrfs_root *root,
                                 u64 dir, const char *name, int name_len,
                                 u64 *found_inode,
                                 u8 *found_type)
{
        int ret = 0;
        struct btrfs_dir_item *di;
        struct btrfs_key key;
        struct btrfs_path *path;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        di = btrfs_lookup_dir_item(NULL, root, path,
                        dir, name, name_len, 0);
        if (!di) {
                ret = -ENOENT;
                goto out;
        }
        if (IS_ERR(di)) {
                ret = PTR_ERR(di);
                goto out;
        }
        btrfs_dir_item_key_to_cpu(path->nodes[0], di, &key);
        if (key.type == BTRFS_ROOT_ITEM_KEY) {
                ret = -ENOENT;
                goto out;
        }
        *found_inode = key.objectid;
        *found_type = btrfs_dir_type(path->nodes[0], di);

out:
        btrfs_free_path(path);
        return ret;
}

/*
 * Looks up the first btrfs_inode_ref of a given ino. It returns the parent dir,
 * generation of the parent dir and the name of the dir entry.
 */
static int get_first_ref(struct btrfs_root *root, u64 ino,
                         u64 *dir, u64 *dir_gen, struct fs_path *name)
{
        int ret;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_path *path;
        int len;
        u64 parent_dir;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = ino;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
        if (ret < 0)
                goto out;
        if (!ret)
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                path->slots[0]);
        if (ret || found_key.objectid != ino ||
            (found_key.type != BTRFS_INODE_REF_KEY &&
             found_key.type != BTRFS_INODE_EXTREF_KEY)) {
                ret = -ENOENT;
                goto out;
        }

        if (found_key.type == BTRFS_INODE_REF_KEY) {
                struct btrfs_inode_ref *iref;
                iref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                      struct btrfs_inode_ref);
                len = btrfs_inode_ref_name_len(path->nodes[0], iref);
                ret = fs_path_add_from_extent_buffer(name, path->nodes[0],
                                                     (unsigned long)(iref + 1),
                                                     len);
                parent_dir = found_key.offset;
        } else {
                struct btrfs_inode_extref *extref;
                extref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                        struct btrfs_inode_extref);
                len = btrfs_inode_extref_name_len(path->nodes[0], extref);
                ret = fs_path_add_from_extent_buffer(name, path->nodes[0],
                                        (unsigned long)&extref->name, len);
                parent_dir = btrfs_inode_extref_parent(path->nodes[0], extref);
        }
        if (ret < 0)
                goto out;
        btrfs_release_path(path);

        if (dir_gen) {
                ret = get_inode_info(root, parent_dir, NULL, dir_gen, NULL,
                                     NULL, NULL, NULL);
                if (ret < 0)
                        goto out;
        }

        *dir = parent_dir;

out:
        btrfs_free_path(path);
        return ret;
}

static int is_first_ref(struct btrfs_root *root,
                        u64 ino, u64 dir,
                        const char *name, int name_len)
{
        int ret;
        struct fs_path *tmp_name;
        u64 tmp_dir;

        tmp_name = fs_path_alloc();
        if (!tmp_name)
                return -ENOMEM;

        ret = get_first_ref(root, ino, &tmp_dir, NULL, tmp_name);
        if (ret < 0)
                goto out;

        if (dir != tmp_dir || name_len != fs_path_len(tmp_name)) {
                ret = 0;
                goto out;
        }

        ret = !memcmp(tmp_name->start, name, name_len);

out:
        fs_path_free(tmp_name);
        return ret;
}

/*
 * Used by process_recorded_refs to determine if a new ref would overwrite an
 * already existing ref. In case it detects an overwrite, it returns the
 * inode/gen in who_ino/who_gen.
 * When an overwrite is detected, process_recorded_refs does proper orphanizing
 * to make sure later references to the overwritten inode are possible.
 * Orphanizing is however only required for the first ref of an inode.
 * process_recorded_refs does an additional is_first_ref check to see if
 * orphanizing is really required.
 */
static int will_overwrite_ref(struct send_ctx *sctx, u64 dir, u64 dir_gen,
                              const char *name, int name_len,
                              u64 *who_ino, u64 *who_gen)
{
        int ret = 0;
        u64 gen;
        u64 other_inode = 0;
        u8 other_type = 0;

        if (!sctx->parent_root)
                goto out;

        ret = is_inode_existent(sctx, dir, dir_gen);
        if (ret <= 0)
                goto out;

        /*
         * If we have a parent root we need to verify that the parent dir was
         * not deleted and then re-created, if it was then we have no overwrite
         * and we can just unlink this entry.
         */
        if (sctx->parent_root) {
                ret = get_inode_info(sctx->parent_root, dir, NULL, &gen, NULL,
                                     NULL, NULL, NULL);
                if (ret < 0 && ret != -ENOENT)
                        goto out;
                if (ret) {
                        ret = 0;
                        goto out;
                }
                if (gen != dir_gen)
                        goto out;
        }

        ret = lookup_dir_item_inode(sctx->parent_root, dir, name, name_len,
                        &other_inode, &other_type);
        if (ret < 0 && ret != -ENOENT)
                goto out;
        if (ret) {
                ret = 0;
                goto out;
        }

        /*
         * Check if the overwritten ref was already processed. If yes, the ref
         * was already unlinked/moved, so we can safely assume that we will not
         * overwrite anything at this point in time.
         */
        if (other_inode > sctx->send_progress ||
            is_waiting_for_move(sctx, other_inode)) {
                ret = get_inode_info(sctx->parent_root, other_inode, NULL,
                                who_gen, NULL, NULL, NULL, NULL);
                if (ret < 0)
                        goto out;

                ret = 1;
                *who_ino = other_inode;
        } else {
                ret = 0;
        }

out:
        return ret;
}

/*
 * Checks if the ref was overwritten by an already processed inode. This is
 * used by __get_cur_name_and_parent to find out if the ref was orphanized and
 * thus the orphan name needs be used.
 * process_recorded_refs also uses it to avoid unlinking of refs that were
 * overwritten.
 */
static int did_overwrite_ref(struct send_ctx *sctx,
                            u64 dir, u64 dir_gen,
                            u64 ino, u64 ino_gen,
                            const char *name, int name_len)
{
        int ret = 0;
        u64 gen;
        u64 ow_inode;
        u8 other_type;

        if (!sctx->parent_root)
                goto out;

        ret = is_inode_existent(sctx, dir, dir_gen);
        if (ret <= 0)
                goto out;

        /* check if the ref was overwritten by another ref */
        ret = lookup_dir_item_inode(sctx->send_root, dir, name, name_len,
                        &ow_inode, &other_type);
        if (ret < 0 && ret != -ENOENT)
                goto out;
        if (ret) {
                /* was never and will never be overwritten */
                ret = 0;
                goto out;
        }

        ret = get_inode_info(sctx->send_root, ow_inode, NULL, &gen, NULL, NULL,
                        NULL, NULL);
        if (ret < 0)
                goto out;

        if (ow_inode == ino && gen == ino_gen) {
                ret = 0;
                goto out;
        }

        /*
         * We know that it is or will be overwritten. Check this now.
         * The current inode being processed might have been the one that caused
         * inode 'ino' to be orphanized, therefore check if ow_inode matches
         * the current inode being processed.
         */
        if ((ow_inode < sctx->send_progress) ||
            (ino != sctx->cur_ino && ow_inode == sctx->cur_ino &&
             gen == sctx->cur_inode_gen))
                ret = 1;
        else
                ret = 0;

out:
        return ret;
}

/*
 * Same as did_overwrite_ref, but also checks if it is the first ref of an inode
 * that got overwritten. This is used by process_recorded_refs to determine
 * if it has to use the path as returned by get_cur_path or the orphan name.
 */
static int did_overwrite_first_ref(struct send_ctx *sctx, u64 ino, u64 gen)
{
        int ret = 0;
        struct fs_path *name = NULL;
        u64 dir;
        u64 dir_gen;

        if (!sctx->parent_root)
                goto out;

        name = fs_path_alloc();
        if (!name)
                return -ENOMEM;

        ret = get_first_ref(sctx->parent_root, ino, &dir, &dir_gen, name);
        if (ret < 0)
                goto out;

        ret = did_overwrite_ref(sctx, dir, dir_gen, ino, gen,
                        name->start, fs_path_len(name));

out:
        fs_path_free(name);
        return ret;
}

/*
 * Insert a name cache entry. On 32bit kernels the radix tree index is 32bit,
 * so we need to do some special handling in case we have clashes. This function
 * takes care of this with the help of name_cache_entry::radix_list.
 * In case of error, nce is kfreed.
 */
static int name_cache_insert(struct send_ctx *sctx,
                             struct name_cache_entry *nce)
{
        int ret = 0;
        struct list_head *nce_head;

        nce_head = radix_tree_lookup(&sctx->name_cache,
                        (unsigned long)nce->ino);
        if (!nce_head) {
                nce_head = kmalloc(sizeof(*nce_head), GFP_KERNEL);
                if (!nce_head) {
                        kfree(nce);
                        return -ENOMEM;
                }
                INIT_LIST_HEAD(nce_head);

                ret = radix_tree_insert(&sctx->name_cache, nce->ino, nce_head);
                if (ret < 0) {
                        kfree(nce_head);
                        kfree(nce);
                        return ret;
                }
        }
        list_add_tail(&nce->radix_list, nce_head);
        list_add_tail(&nce->list, &sctx->name_cache_list);
        sctx->name_cache_size++;

        return ret;
}

static void name_cache_delete(struct send_ctx *sctx,
                              struct name_cache_entry *nce)
{
        struct list_head *nce_head;

        nce_head = radix_tree_lookup(&sctx->name_cache,
                        (unsigned long)nce->ino);
        if (!nce_head) {
                btrfs_err(sctx->send_root->fs_info,
              "name_cache_delete lookup failed ino %llu cache size %d, leaking memory",
                        nce->ino, sctx->name_cache_size);
        }

        list_del(&nce->radix_list);
        list_del(&nce->list);
        sctx->name_cache_size--;

        /*
         * We may not get to the final release of nce_head if the lookup fails
         */
        if (nce_head && list_empty(nce_head)) {
                radix_tree_delete(&sctx->name_cache, (unsigned long)nce->ino);
                kfree(nce_head);
        }
}

static struct name_cache_entry *name_cache_search(struct send_ctx *sctx,
                                                    u64 ino, u64 gen)
{
        struct list_head *nce_head;
        struct name_cache_entry *cur;

        nce_head = radix_tree_lookup(&sctx->name_cache, (unsigned long)ino);
        if (!nce_head)
                return NULL;

        list_for_each_entry(cur, nce_head, radix_list) {
                if (cur->ino == ino && cur->gen == gen)
                        return cur;
        }
        return NULL;
}

/*
 * Removes the entry from the list and adds it back to the end. This marks the
 * entry as recently used so that name_cache_clean_unused does not remove it.
 */
static void name_cache_used(struct send_ctx *sctx, struct name_cache_entry *nce)
{
        list_del(&nce->list);
        list_add_tail(&nce->list, &sctx->name_cache_list);
}

/*
 * Remove some entries from the beginning of name_cache_list.
 */
static void name_cache_clean_unused(struct send_ctx *sctx)
{
        struct name_cache_entry *nce;

        if (sctx->name_cache_size < SEND_CTX_NAME_CACHE_CLEAN_SIZE)
                return;

        while (sctx->name_cache_size > SEND_CTX_MAX_NAME_CACHE_SIZE) {
                nce = list_entry(sctx->name_cache_list.next,
                                struct name_cache_entry, list);
                name_cache_delete(sctx, nce);
                kfree(nce);
        }
}

static void name_cache_free(struct send_ctx *sctx)
{
        struct name_cache_entry *nce;

        while (!list_empty(&sctx->name_cache_list)) {
                nce = list_entry(sctx->name_cache_list.next,
                                struct name_cache_entry, list);
                name_cache_delete(sctx, nce);
                kfree(nce);
        }
}

/*
 * Used by get_cur_path for each ref up to the root.
 * Returns 0 if it succeeded.
 * Returns 1 if the inode is not existent or got overwritten. In that case, the
 * name is an orphan name. This instructs get_cur_path to stop iterating. If 1
 * is returned, parent_ino/parent_gen are not guaranteed to be valid.
 * Returns <0 in case of error.
 */
static int __get_cur_name_and_parent(struct send_ctx *sctx,
                                     u64 ino, u64 gen,
                                     u64 *parent_ino,
                                     u64 *parent_gen,
                                     struct fs_path *dest)
{
        int ret;
        int nce_ret;
        struct name_cache_entry *nce = NULL;

        /*
         * First check if we already did a call to this function with the same
         * ino/gen. If yes, check if the cache entry is still up-to-date. If yes
         * return the cached result.
         */
        nce = name_cache_search(sctx, ino, gen);
        if (nce) {
                if (ino < sctx->send_progress && nce->need_later_update) {
                        name_cache_delete(sctx, nce);
                        kfree(nce);
                        nce = NULL;
                } else {
                        name_cache_used(sctx, nce);
                        *parent_ino = nce->parent_ino;
                        *parent_gen = nce->parent_gen;
                        ret = fs_path_add(dest, nce->name, nce->name_len);
                        if (ret < 0)
                                goto out;
                        ret = nce->ret;
                        goto out;
                }
        }

        /*
         * If the inode is not existent yet, add the orphan name and return 1.
         * This should only happen for the parent dir that we determine in
         * __record_new_ref
         */
        ret = is_inode_existent(sctx, ino, gen);
        if (ret < 0)
                goto out;

        if (!ret) {
                ret = gen_unique_name(sctx, ino, gen, dest);
                if (ret < 0)
                        goto out;
                ret = 1;
                goto out_cache;
        }

        /*
         * Depending on whether the inode was already processed or not, use
         * send_root or parent_root for ref lookup.
         */
        if (ino < sctx->send_progress)
                ret = get_first_ref(sctx->send_root, ino,
                                    parent_ino, parent_gen, dest);
        else
                ret = get_first_ref(sctx->parent_root, ino,
                                    parent_ino, parent_gen, dest);
        if (ret < 0)
                goto out;

        /*
         * Check if the ref was overwritten by an inode's ref that was processed
         * earlier. If yes, treat as orphan and return 1.
         */
        ret = did_overwrite_ref(sctx, *parent_ino, *parent_gen, ino, gen,
                        dest->start, dest->end - dest->start);
        if (ret < 0)
                goto out;
        if (ret) {
                fs_path_reset(dest);
                ret = gen_unique_name(sctx, ino, gen, dest);
                if (ret < 0)
                        goto out;
                ret = 1;
        }

out_cache:
        /*
         * Store the result of the lookup in the name cache.
         */
        nce = kmalloc(sizeof(*nce) + fs_path_len(dest) + 1, GFP_KERNEL);
        if (!nce) {
                ret = -ENOMEM;
                goto out;
        }

        nce->ino = ino;
        nce->gen = gen;
        nce->parent_ino = *parent_ino;
        nce->parent_gen = *parent_gen;
        nce->name_len = fs_path_len(dest);
        nce->ret = ret;
        strcpy(nce->name, dest->start);

        if (ino < sctx->send_progress)
                nce->need_later_update = 0;
        else
                nce->need_later_update = 1;

        nce_ret = name_cache_insert(sctx, nce);
        if (nce_ret < 0)
                ret = nce_ret;
        name_cache_clean_unused(sctx);

out:
        return ret;
}

/*
 * Magic happens here. This function returns the first ref to an inode as it
 * would look like while receiving the stream at this point in time.
 * We walk the path up to the root. For every inode in between, we check if it
 * was already processed/sent. If yes, we continue with the parent as found
 * in send_root. If not, we continue with the parent as found in parent_root.
 * If we encounter an inode that was deleted at this point in time, we use the
 * inodes "orphan" name instead of the real name and stop. Same with new inodes
 * that were not created yet and overwritten inodes/refs.
 *
 * When do we have have orphan inodes:
 * 1. When an inode is freshly created and thus no valid refs are available yet
 * 2. When a directory lost all it's refs (deleted) but still has dir items
 *    inside which were not processed yet (pending for move/delete). If anyone
 *    tried to get the path to the dir items, it would get a path inside that
 *    orphan directory.
 * 3. When an inode is moved around or gets new links, it may overwrite the ref
 *    of an unprocessed inode. If in that case the first ref would be
 *    overwritten, the overwritten inode gets "orphanized". Later when we
 *    process this overwritten inode, it is restored at a new place by moving
 *    the orphan inode.
 *
 * sctx->send_progress tells this function at which point in time receiving
 * would be.
 */
static int get_cur_path(struct send_ctx *sctx, u64 ino, u64 gen,
                        struct fs_path *dest)
{
        int ret = 0;
        struct fs_path *name = NULL;
        u64 parent_inode = 0;
        u64 parent_gen = 0;
        int stop = 0;

        name = fs_path_alloc();
        if (!name) {
                ret = -ENOMEM;
                goto out;
        }

        dest->reversed = 1;
        fs_path_reset(dest);

        while (!stop && ino != BTRFS_FIRST_FREE_OBJECTID) {
                struct waiting_dir_move *wdm;

                fs_path_reset(name);

                if (is_waiting_for_rm(sctx, ino)) {
                        ret = gen_unique_name(sctx, ino, gen, name);
                        if (ret < 0)
                                goto out;
                        ret = fs_path_add_path(dest, name);
                        break;
                }

                wdm = get_waiting_dir_move(sctx, ino);
                if (wdm && wdm->orphanized) {
                        ret = gen_unique_name(sctx, ino, gen, name);
                        stop = 1;
                } else if (wdm) {
                        ret = get_first_ref(sctx->parent_root, ino,
                                            &parent_inode, &parent_gen, name);
                } else {
                        ret = __get_cur_name_and_parent(sctx, ino, gen,
                                                        &parent_inode,
                                                        &parent_gen, name);
                        if (ret)
                                stop = 1;
                }

                if (ret < 0)
                        goto out;

                ret = fs_path_add_path(dest, name);
                if (ret < 0)
                        goto out;

                ino = parent_inode;
                gen = parent_gen;
        }

out:
        fs_path_free(name);
        if (!ret)
                fs_path_unreverse(dest);
        return ret;
}

/*
 * Sends a BTRFS_SEND_C_SUBVOL command/item to userspace
 */
static int send_subvol_begin(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_root *send_root = sctx->send_root;
        struct btrfs_root *parent_root = sctx->parent_root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_root_ref *ref;
        struct extent_buffer *leaf;
        char *name = NULL;
        int namelen;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        name = kmalloc(BTRFS_PATH_NAME_MAX, GFP_KERNEL);
        if (!name) {
                btrfs_free_path(path);
                return -ENOMEM;
        }

        key.objectid = send_root->objectid;
        key.type = BTRFS_ROOT_BACKREF_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(send_root->fs_info->tree_root,
                                &key, path, 1, 0);
        if (ret < 0)
                goto out;
        if (ret) {
                ret = -ENOENT;
                goto out;
        }

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.type != BTRFS_ROOT_BACKREF_KEY ||
            key.objectid != send_root->objectid) {
                ret = -ENOENT;
                goto out;
        }
        ref = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_ref);
        namelen = btrfs_root_ref_name_len(leaf, ref);
        read_extent_buffer(leaf, name, (unsigned long)(ref + 1), namelen);
        btrfs_release_path(path);

        if (parent_root) {
                ret = begin_cmd(sctx, BTRFS_SEND_C_SNAPSHOT);
                if (ret < 0)
                        goto out;
        } else {
                ret = begin_cmd(sctx, BTRFS_SEND_C_SUBVOL);
                if (ret < 0)
                        goto out;
        }

        TLV_PUT_STRING(sctx, BTRFS_SEND_A_PATH, name, namelen);

        if (!btrfs_is_empty_uuid(sctx->send_root->root_item.received_uuid))
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_UUID,
                            sctx->send_root->root_item.received_uuid);
        else
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_UUID,
                            sctx->send_root->root_item.uuid);

        TLV_PUT_U64(sctx, BTRFS_SEND_A_CTRANSID,
                    le64_to_cpu(sctx->send_root->root_item.ctransid));
        if (parent_root) {
                if (!btrfs_is_empty_uuid(parent_root->root_item.received_uuid))
                        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                                     parent_root->root_item.received_uuid);
                else
                        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                                     parent_root->root_item.uuid);
                TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                            le64_to_cpu(sctx->parent_root->root_item.ctransid));
        }

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        btrfs_free_path(path);
        kfree(name);
        return ret;
}

static int send_truncate(struct send_ctx *sctx, u64 ino, u64 gen, u64 size)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct fs_path *p;

        btrfs_debug(fs_info, "send_truncate %llu size=%llu", ino, size);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = begin_cmd(sctx, BTRFS_SEND_C_TRUNCATE);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, ino, gen, p);
        if (ret < 0)
                goto out;
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, size);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

static int send_chmod(struct send_ctx *sctx, u64 ino, u64 gen, u64 mode)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct fs_path *p;

        btrfs_debug(fs_info, "send_chmod %llu mode=%llu", ino, mode);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = begin_cmd(sctx, BTRFS_SEND_C_CHMOD);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, ino, gen, p);
        if (ret < 0)
                goto out;
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_MODE, mode & 07777);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

static int send_chown(struct send_ctx *sctx, u64 ino, u64 gen, u64 uid, u64 gid)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct fs_path *p;

        btrfs_debug(fs_info, "send_chown %llu uid=%llu, gid=%llu",
                    ino, uid, gid);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = begin_cmd(sctx, BTRFS_SEND_C_CHOWN);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, ino, gen, p);
        if (ret < 0)
                goto out;
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UID, uid);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_GID, gid);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

static int send_utimes(struct send_ctx *sctx, u64 ino, u64 gen)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct fs_path *p = NULL;
        struct btrfs_inode_item *ii;
        struct btrfs_path *path = NULL;
        struct extent_buffer *eb;
        struct btrfs_key key;
        int slot;

        btrfs_debug(fs_info, "send_utimes %llu", ino);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        path = alloc_path_for_send();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        key.objectid = ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, sctx->send_root, &key, path, 0, 0);
        if (ret > 0)
                ret = -ENOENT;
        if (ret < 0)
                goto out;

        eb = path->nodes[0];
        slot = path->slots[0];
        ii = btrfs_item_ptr(eb, slot, struct btrfs_inode_item);

        ret = begin_cmd(sctx, BTRFS_SEND_C_UTIMES);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, ino, gen, p);
        if (ret < 0)
                goto out;
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_ATIME, eb, &ii->atime);
        TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_MTIME, eb, &ii->mtime);
        TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_CTIME, eb, &ii->ctime);
        /* TODO Add otime support when the otime patches get into upstream */

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        btrfs_free_path(path);
        return ret;
}

/*
 * Sends a BTRFS_SEND_C_MKXXX or SYMLINK command to user space. We don't have
 * a valid path yet because we did not process the refs yet. So, the inode
 * is created as orphan.
 */
static int send_create_inode(struct send_ctx *sctx, u64 ino)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct fs_path *p;
        int cmd;
        u64 gen;
        u64 mode;
        u64 rdev;

        btrfs_debug(fs_info, "send_create_inode %llu", ino);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        if (ino != sctx->cur_ino) {
                ret = get_inode_info(sctx->send_root, ino, NULL, &gen, &mode,
                                     NULL, NULL, &rdev);
                if (ret < 0)
                        goto out;
        } else {
                gen = sctx->cur_inode_gen;
                mode = sctx->cur_inode_mode;
                rdev = sctx->cur_inode_rdev;
        }

        if (S_ISREG(mode)) {
                cmd = BTRFS_SEND_C_MKFILE;
        } else if (S_ISDIR(mode)) {
                cmd = BTRFS_SEND_C_MKDIR;
        } else if (S_ISLNK(mode)) {
                cmd = BTRFS_SEND_C_SYMLINK;
        } else if (S_ISCHR(mode) || S_ISBLK(mode)) {
                cmd = BTRFS_SEND_C_MKNOD;
        } else if (S_ISFIFO(mode)) {
                cmd = BTRFS_SEND_C_MKFIFO;
        } else if (S_ISSOCK(mode)) {
                cmd = BTRFS_SEND_C_MKSOCK;
        } else {
                btrfs_warn(sctx->send_root->fs_info, "unexpected inode type %o",
                                (int)(mode & S_IFMT));
                ret = -ENOTSUPP;
                goto out;
        }

        ret = begin_cmd(sctx, cmd);
        if (ret < 0)
                goto out;

        ret = gen_unique_name(sctx, ino, gen, p);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_INO, ino);

        if (S_ISLNK(mode)) {
                fs_path_reset(p);
                ret = read_symlink(sctx->send_root, ino, p);
                if (ret < 0)
                        goto out;
                TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_LINK, p);
        } else if (S_ISCHR(mode) || S_ISBLK(mode) ||
                   S_ISFIFO(mode) || S_ISSOCK(mode)) {
                TLV_PUT_U64(sctx, BTRFS_SEND_A_RDEV, new_encode_dev(rdev));
                TLV_PUT_U64(sctx, BTRFS_SEND_A_MODE, mode);
        }

        ret = send_cmd(sctx);
        if (ret < 0)
                goto out;


tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

/*
 * We need some special handling for inodes that get processed before the parent
 * directory got created. See process_recorded_refs for details.
 * This function does the check if we already created the dir out of order.
 */
static int did_create_dir(struct send_ctx *sctx, u64 dir)
{
        int ret = 0;
        struct btrfs_path *path = NULL;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_key di_key;
        struct extent_buffer *eb;
        struct btrfs_dir_item *di;
        int slot;

        path = alloc_path_for_send();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        key.objectid = dir;
        key.type = BTRFS_DIR_INDEX_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, sctx->send_root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                eb = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(eb)) {
                        ret = btrfs_next_leaf(sctx->send_root, path);
                        if (ret < 0) {
                                goto out;
                        } else if (ret > 0) {
                                ret = 0;
                                break;
                        }
                        continue;
                }

                btrfs_item_key_to_cpu(eb, &found_key, slot);
                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        ret = 0;
                        goto out;
                }

                di = btrfs_item_ptr(eb, slot, struct btrfs_dir_item);
                btrfs_dir_item_key_to_cpu(eb, di, &di_key);

                if (di_key.type != BTRFS_ROOT_ITEM_KEY &&
                    di_key.objectid < sctx->send_progress) {
                        ret = 1;
                        goto out;
                }

                path->slots[0]++;
        }

out:
        btrfs_free_path(path);
        return ret;
}

/*
 * Only creates the inode if it is:
 * 1. Not a directory
 * 2. Or a directory which was not created already due to out of order
 *    directories. See did_create_dir and process_recorded_refs for details.
 */
static int send_create_inode_if_needed(struct send_ctx *sctx)
{
        int ret;

        if (S_ISDIR(sctx->cur_inode_mode)) {
                ret = did_create_dir(sctx, sctx->cur_ino);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = 0;
                        goto out;
                }
        }

        ret = send_create_inode(sctx, sctx->cur_ino);
        if (ret < 0)
                goto out;

out:
        return ret;
}

struct recorded_ref {
        struct list_head list;
        char *dir_path;
        char *name;
        struct fs_path *full_path;
        u64 dir;
        u64 dir_gen;
        int dir_path_len;
        int name_len;
};

/*
 * We need to process new refs before deleted refs, but compare_tree gives us
 * everything mixed. So we first record all refs and later process them.
 * This function is a helper to record one ref.
 */
static int __record_ref(struct list_head *head, u64 dir,
                      u64 dir_gen, struct fs_path *path)
{
        struct recorded_ref *ref;

        ref = kmalloc(sizeof(*ref), GFP_KERNEL);
        if (!ref)
                return -ENOMEM;

        ref->dir = dir;
        ref->dir_gen = dir_gen;
        ref->full_path = path;

        ref->name = (char *)kbasename(ref->full_path->start);
        ref->name_len = ref->full_path->end - ref->name;
        ref->dir_path = ref->full_path->start;
        if (ref->name == ref->full_path->start)
                ref->dir_path_len = 0;
        else
                ref->dir_path_len = ref->full_path->end -
                                ref->full_path->start - 1 - ref->name_len;

        list_add_tail(&ref->list, head);
        return 0;
}

static int dup_ref(struct recorded_ref *ref, struct list_head *list)
{
        struct recorded_ref *new;

        new = kmalloc(sizeof(*ref), GFP_KERNEL);
        if (!new)
                return -ENOMEM;

        new->dir = ref->dir;
        new->dir_gen = ref->dir_gen;
        new->full_path = NULL;
        INIT_LIST_HEAD(&new->list);
        list_add_tail(&new->list, list);
        return 0;
}

static void __free_recorded_refs(struct list_head *head)
{
        struct recorded_ref *cur;

        while (!list_empty(head)) {
                cur = list_entry(head->next, struct recorded_ref, list);
                fs_path_free(cur->full_path);
                list_del(&cur->list);
                kfree(cur);
        }
}

static void free_recorded_refs(struct send_ctx *sctx)
{
        __free_recorded_refs(&sctx->new_refs);
        __free_recorded_refs(&sctx->deleted_refs);
}

/*
 * Renames/moves a file/dir to its orphan name. Used when the first
 * ref of an unprocessed inode gets overwritten and for all non empty
 * directories.
 */
static int orphanize_inode(struct send_ctx *sctx, u64 ino, u64 gen,
                          struct fs_path *path)
{
        int ret;
        struct fs_path *orphan;

        orphan = fs_path_alloc();
        if (!orphan)
                return -ENOMEM;

        ret = gen_unique_name(sctx, ino, gen, orphan);
        if (ret < 0)
                goto out;

        ret = send_rename(sctx, path, orphan);

out:
        fs_path_free(orphan);
        return ret;
}

static struct orphan_dir_info *
add_orphan_dir_info(struct send_ctx *sctx, u64 dir_ino)
{
        struct rb_node **p = &sctx->orphan_dirs.rb_node;
        struct rb_node *parent = NULL;
        struct orphan_dir_info *entry, *odi;

        odi = kmalloc(sizeof(*odi), GFP_KERNEL);
        if (!odi)
                return ERR_PTR(-ENOMEM);
        odi->ino = dir_ino;
        odi->gen = 0;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct orphan_dir_info, node);
                if (dir_ino < entry->ino) {
                        p = &(*p)->rb_left;
                } else if (dir_ino > entry->ino) {
                        p = &(*p)->rb_right;
                } else {
                        kfree(odi);
                        return entry;
                }
        }

        rb_link_node(&odi->node, parent, p);
        rb_insert_color(&odi->node, &sctx->orphan_dirs);
        return odi;
}

static struct orphan_dir_info *
get_orphan_dir_info(struct send_ctx *sctx, u64 dir_ino)
{
        struct rb_node *n = sctx->orphan_dirs.rb_node;
        struct orphan_dir_info *entry;

        while (n) {
                entry = rb_entry(n, struct orphan_dir_info, node);
                if (dir_ino < entry->ino)
                        n = n->rb_left;
                else if (dir_ino > entry->ino)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

static int is_waiting_for_rm(struct send_ctx *sctx, u64 dir_ino)
{
        struct orphan_dir_info *odi = get_orphan_dir_info(sctx, dir_ino);

        return odi != NULL;
}

static void free_orphan_dir_info(struct send_ctx *sctx,
                                 struct orphan_dir_info *odi)
{
        if (!odi)
                return;
        rb_erase(&odi->node, &sctx->orphan_dirs);
        kfree(odi);
}

/*
 * Returns 1 if a directory can be removed at this point in time.
 * We check this by iterating all dir items and checking if the inode behind
 * the dir item was already processed.
 */
static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 dir_gen,
                     u64 send_progress)
{
        int ret = 0;
        struct btrfs_root *root = sctx->parent_root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_key loc;
        struct btrfs_dir_item *di;

        /*
         * Don't try to rmdir the top/root subvolume dir.
         */
        if (dir == BTRFS_FIRST_FREE_OBJECTID)
                return 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = dir;
        key.type = BTRFS_DIR_INDEX_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                struct waiting_dir_move *dm;

                if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto out;
                        else if (ret > 0)
                                break;
                        continue;
                }
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                      path->slots[0]);
                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type)
                        break;

                di = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                struct btrfs_dir_item);
                btrfs_dir_item_key_to_cpu(path->nodes[0], di, &loc);

                dm = get_waiting_dir_move(sctx, loc.objectid);
                if (dm) {
                        struct orphan_dir_info *odi;

                        odi = add_orphan_dir_info(sctx, dir);
                        if (IS_ERR(odi)) {
                                ret = PTR_ERR(odi);
                                goto out;
                        }
                        odi->gen = dir_gen;
                        dm->rmdir_ino = dir;
                        ret = 0;
                        goto out;
                }

                if (loc.objectid > send_progress) {
                        struct orphan_dir_info *odi;

                        odi = get_orphan_dir_info(sctx, dir);
                        free_orphan_dir_info(sctx, odi);
                        ret = 0;
                        goto out;
                }

                path->slots[0]++;
        }

        ret = 1;

out:
        btrfs_free_path(path);
        return ret;
}

static int is_waiting_for_move(struct send_ctx *sctx, u64 ino)
{
        struct waiting_dir_move *entry = get_waiting_dir_move(sctx, ino);

        return entry != NULL;
}

static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino, bool orphanized)
{
        struct rb_node **p = &sctx->waiting_dir_moves.rb_node;
        struct rb_node *parent = NULL;
        struct waiting_dir_move *entry, *dm;

        dm = kmalloc(sizeof(*dm), GFP_KERNEL);
        if (!dm)
                return -ENOMEM;
        dm->ino = ino;
        dm->rmdir_ino = 0;
        dm->orphanized = orphanized;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct waiting_dir_move, node);
                if (ino < entry->ino) {
                        p = &(*p)->rb_left;
                } else if (ino > entry->ino) {
                        p = &(*p)->rb_right;
                } else {
                        kfree(dm);
                        return -EEXIST;
                }
        }

        rb_link_node(&dm->node, parent, p);
        rb_insert_color(&dm->node, &sctx->waiting_dir_moves);
        return 0;
}

static struct waiting_dir_move *
get_waiting_dir_move(struct send_ctx *sctx, u64 ino)
{
        struct rb_node *n = sctx->waiting_dir_moves.rb_node;
        struct waiting_dir_move *entry;

        while (n) {
                entry = rb_entry(n, struct waiting_dir_move, node);
                if (ino < entry->ino)
                        n = n->rb_left;
                else if (ino > entry->ino)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

static void free_waiting_dir_move(struct send_ctx *sctx,
                                  struct waiting_dir_move *dm)
{
        if (!dm)
                return;
        rb_erase(&dm->node, &sctx->waiting_dir_moves);
        kfree(dm);
}

static int add_pending_dir_move(struct send_ctx *sctx,
                                u64 ino,
                                u64 ino_gen,
                                u64 parent_ino,
                                struct list_head *new_refs,
                                struct list_head *deleted_refs,
                                const bool is_orphan)
{
        struct rb_node **p = &sctx->pending_dir_moves.rb_node;
        struct rb_node *parent = NULL;
        struct pending_dir_move *entry = NULL, *pm;
        struct recorded_ref *cur;
        int exists = 0;
        int ret;

        pm = kmalloc(sizeof(*pm), GFP_KERNEL);
        if (!pm)
                return -ENOMEM;
        pm->parent_ino = parent_ino;
        pm->ino = ino;
        pm->gen = ino_gen;
        INIT_LIST_HEAD(&pm->list);
        INIT_LIST_HEAD(&pm->update_refs);
        RB_CLEAR_NODE(&pm->node);

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct pending_dir_move, node);
                if (parent_ino < entry->parent_ino) {
                        p = &(*p)->rb_left;
                } else if (parent_ino > entry->parent_ino) {
                        p = &(*p)->rb_right;
                } else {
                        exists = 1;
                        break;
                }
        }

        list_for_each_entry(cur, deleted_refs, list) {
                ret = dup_ref(cur, &pm->update_refs);
                if (ret < 0)
                        goto out;
        }
        list_for_each_entry(cur, new_refs, list) {
                ret = dup_ref(cur, &pm->update_refs);
                if (ret < 0)
                        goto out;
        }

        ret = add_waiting_dir_move(sctx, pm->ino, is_orphan);
        if (ret)
                goto out;

        if (exists) {
                list_add_tail(&pm->list, &entry->list);
        } else {
                rb_link_node(&pm->node, parent, p);
                rb_insert_color(&pm->node, &sctx->pending_dir_moves);
        }
        ret = 0;
out:
        if (ret) {
                __free_recorded_refs(&pm->update_refs);
                kfree(pm);
        }
        return ret;
}

static struct pending_dir_move *get_pending_dir_moves(struct send_ctx *sctx,
                                                      u64 parent_ino)
{
        struct rb_node *n = sctx->pending_dir_moves.rb_node;
        struct pending_dir_move *entry;

        while (n) {
                entry = rb_entry(n, struct pending_dir_move, node);
                if (parent_ino < entry->parent_ino)
                        n = n->rb_left;
                else if (parent_ino > entry->parent_ino)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

static int path_loop(struct send_ctx *sctx, struct fs_path *name,
                     u64 ino, u64 gen, u64 *ancestor_ino)
{
        int ret = 0;
        u64 parent_inode = 0;
        u64 parent_gen = 0;
        u64 start_ino = ino;

        *ancestor_ino = 0;
        while (ino != BTRFS_FIRST_FREE_OBJECTID) {
                fs_path_reset(name);

                if (is_waiting_for_rm(sctx, ino))
                        break;
                if (is_waiting_for_move(sctx, ino)) {
                        if (*ancestor_ino == 0)
                                *ancestor_ino = ino;
                        ret = get_first_ref(sctx->parent_root, ino,
                                            &parent_inode, &parent_gen, name);
                } else {
                        ret = __get_cur_name_and_parent(sctx, ino, gen,
                                                        &parent_inode,
                                                        &parent_gen, name);
                        if (ret > 0) {
                                ret = 0;
                                break;
                        }
                }
                if (ret < 0)
                        break;
                if (parent_inode == start_ino) {
                        ret = 1;
                        if (*ancestor_ino == 0)
                                *ancestor_ino = ino;
                        break;
                }
                ino = parent_inode;
                gen = parent_gen;
        }
        return ret;
}

static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
{
        struct fs_path *from_path = NULL;
        struct fs_path *to_path = NULL;
        struct fs_path *name = NULL;
        u64 orig_progress = sctx->send_progress;
        struct recorded_ref *cur;
        u64 parent_ino, parent_gen;
        struct waiting_dir_move *dm = NULL;
        u64 rmdir_ino = 0;
        u64 ancestor;
        bool is_orphan;
        int ret;

        name = fs_path_alloc();
        from_path = fs_path_alloc();
        if (!name || !from_path) {
                ret = -ENOMEM;
                goto out;
        }

        dm = get_waiting_dir_move(sctx, pm->ino);
        ASSERT(dm);
        rmdir_ino = dm->rmdir_ino;
        is_orphan = dm->orphanized;
        free_waiting_dir_move(sctx, dm);

        if (is_orphan) {
                ret = gen_unique_name(sctx, pm->ino,
                                      pm->gen, from_path);
        } else {
                ret = get_first_ref(sctx->parent_root, pm->ino,
                                    &parent_ino, &parent_gen, name);
                if (ret < 0)
                        goto out;
                ret = get_cur_path(sctx, parent_ino, parent_gen,
                                   from_path);
                if (ret < 0)
                        goto out;
                ret = fs_path_add_path(from_path, name);
        }
        if (ret < 0)
                goto out;

        sctx->send_progress = sctx->cur_ino + 1;
        ret = path_loop(sctx, name, pm->ino, pm->gen, &ancestor);
        if (ret < 0)
                goto out;
        if (ret) {
                LIST_HEAD(deleted_refs);
                ASSERT(ancestor > BTRFS_FIRST_FREE_OBJECTID);
                ret = add_pending_dir_move(sctx, pm->ino, pm->gen, ancestor,
                                           &pm->update_refs, &deleted_refs,
                                           is_orphan);
                if (ret < 0)
                        goto out;
                if (rmdir_ino) {
                        dm = get_waiting_dir_move(sctx, pm->ino);
                        ASSERT(dm);
                        dm->rmdir_ino = rmdir_ino;
                }
                goto out;
        }
        fs_path_reset(name);
        to_path = name;
        name = NULL;
        ret = get_cur_path(sctx, pm->ino, pm->gen, to_path);
        if (ret < 0)
                goto out;

        ret = send_rename(sctx, from_path, to_path);
        if (ret < 0)
                goto out;

        if (rmdir_ino) {
                struct orphan_dir_info *odi;

                odi = get_orphan_dir_info(sctx, rmdir_ino);
                if (!odi) {
                        /* already deleted */
                        goto finish;
                }
                ret = can_rmdir(sctx, rmdir_ino, odi->gen, sctx->cur_ino);
                if (ret < 0)
                        goto out;
                if (!ret)
                        goto finish;

                name = fs_path_alloc();
                if (!name) {
                        ret = -ENOMEM;
                        goto out;
                }
                ret = get_cur_path(sctx, rmdir_ino, odi->gen, name);
                if (ret < 0)
                        goto out;
                ret = send_rmdir(sctx, name);
                if (ret < 0)
                        goto out;
                free_orphan_dir_info(sctx, odi);
        }

finish:
        ret = send_utimes(sctx, pm->ino, pm->gen);
        if (ret < 0)
                goto out;

        /*
         * After rename/move, need to update the utimes of both new parent(s)
         * and old parent(s).
         */
        list_for_each_entry(cur, &pm->update_refs, list) {
                /*
                 * The parent inode might have been deleted in the send snapshot
                 */
                ret = get_inode_info(sctx->send_root, cur->dir, NULL,
                                     NULL, NULL, NULL, NULL, NULL);
                if (ret == -ENOENT) {
                        ret = 0;
                        continue;
                }
                if (ret < 0)
                        goto out;

                ret = send_utimes(sctx, cur->dir, cur->dir_gen);
                if (ret < 0)
                        goto out;
        }

out:
        fs_path_free(name);
        fs_path_free(from_path);
        fs_path_free(to_path);
        sctx->send_progress = orig_progress;

        return ret;
}

static void free_pending_move(struct send_ctx *sctx, struct pending_dir_move *m)
{
        if (!list_empty(&m->list))
                list_del(&m->list);
        if (!RB_EMPTY_NODE(&m->node))
                rb_erase(&m->node, &sctx->pending_dir_moves);
        __free_recorded_refs(&m->update_refs);
        kfree(m);
}

static void tail_append_pending_moves(struct pending_dir_move *moves,
                                      struct list_head *stack)
{
        if (list_empty(&moves->list)) {
                list_add_tail(&moves->list, stack);
        } else {
                LIST_HEAD(list);
                list_splice_init(&moves->list, &list);
                list_add_tail(&moves->list, stack);
                list_splice_tail(&list, stack);
        }
}

static int apply_children_dir_moves(struct send_ctx *sctx)
{
        struct pending_dir_move *pm;
        struct list_head stack;
        u64 parent_ino = sctx->cur_ino;
        int ret = 0;

        pm = get_pending_dir_moves(sctx, parent_ino);
        if (!pm)
                return 0;

        INIT_LIST_HEAD(&stack);
        tail_append_pending_moves(pm, &stack);

        while (!list_empty(&stack)) {
                pm = list_first_entry(&stack, struct pending_dir_move, list);
                parent_ino = pm->ino;
                ret = apply_dir_move(sctx, pm);
                free_pending_move(sctx, pm);
                if (ret)
                        goto out;
                pm = get_pending_dir_moves(sctx, parent_ino);
                if (pm)
                        tail_append_pending_moves(pm, &stack);
        }
        return 0;

out:
        while (!list_empty(&stack)) {
                pm = list_first_entry(&stack, struct pending_dir_move, list);
                free_pending_move(sctx, pm);
        }
        return ret;
}

/*
 * We might need to delay a directory rename even when no ancestor directory
 * (in the send root) with a higher inode number than ours (sctx->cur_ino) was
 * renamed. This happens when we rename a directory to the old name (the name
 * in the parent root) of some other unrelated directory that got its rename
 * delayed due to some ancestor with higher number that got renamed.
 *
 * Example:
 *
 * Parent snapshot:
 * .                                       (ino 256)
 * |---- a/                                (ino 257)
 * |     |---- file                        (ino 260)
 * |
 * |---- b/                                (ino 258)
 * |---- c/                                (ino 259)
 *
 * Send snapshot:
 * .                                       (ino 256)
 * |---- a/                                (ino 258)
 * |---- x/                                (ino 259)
 *       |---- y/                          (ino 257)
 *             |----- file                 (ino 260)
 *
 * Here we can not rename 258 from 'b' to 'a' without the rename of inode 257
 * from 'a' to 'x/y' happening first, which in turn depends on the rename of
 * inode 259 from 'c' to 'x'. So the order of rename commands the send stream
 * must issue is:
 *
 * 1 - rename 259 from 'c' to 'x'
 * 2 - rename 257 from 'a' to 'x/y'
 * 3 - rename 258 from 'b' to 'a'
 *
 * Returns 1 if the rename of sctx->cur_ino needs to be delayed, 0 if it can
 * be done right away and < 0 on error.
 */
static int wait_for_dest_dir_move(struct send_ctx *sctx,
                                  struct recorded_ref *parent_ref,
                                  const bool is_orphan)
{
        struct btrfs_fs_info *fs_info = sctx->parent_root->fs_info;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key di_key;
        struct btrfs_dir_item *di;
        u64 left_gen;
        u64 right_gen;
        int ret = 0;
        struct waiting_dir_move *wdm;

        if (RB_EMPTY_ROOT(&sctx->waiting_dir_moves))
                return 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = parent_ref->dir;
        key.type = BTRFS_DIR_ITEM_KEY;
        key.offset = btrfs_name_hash(parent_ref->name, parent_ref->name_len);

        ret = btrfs_search_slot(NULL, sctx->parent_root, &key, path, 0, 0);
        if (ret < 0) {
                goto out;
        } else if (ret > 0) {
                ret = 0;
                goto out;
        }

        di = btrfs_match_dir_item_name(fs_info, path, parent_ref->name,
                                       parent_ref->name_len);
        if (!di) {
                ret = 0;
                goto out;
        }
        /*
         * di_key.objectid has the number of the inode that has a dentry in the
         * parent directory with the same name that sctx->cur_ino is being
         * renamed to. We need to check if that inode is in the send root as
         * well and if it is currently marked as an inode with a pending rename,
         * if it is, we need to delay the rename of sctx->cur_ino as well, so
         * that it happens after that other inode is renamed.
         */
        btrfs_dir_item_key_to_cpu(path->nodes[0], di, &di_key);
        if (di_key.type != BTRFS_INODE_ITEM_KEY) {
                ret = 0;
                goto out;
        }

        ret = get_inode_info(sctx->parent_root, di_key.objectid, NULL,
                             &left_gen, NULL, NULL, NULL, NULL);
        if (ret < 0)
                goto out;
        ret = get_inode_info(sctx->send_root, di_key.objectid, NULL,
                             &right_gen, NULL, NULL, NULL, NULL);
        if (ret < 0) {
                if (ret == -ENOENT)
                        ret = 0;
                goto out;
        }

        /* Different inode, no need to delay the rename of sctx->cur_ino */
        if (right_gen != left_gen) {
                ret = 0;
                goto out;
        }

        wdm = get_waiting_dir_move(sctx, di_key.objectid);
        if (wdm && !wdm->orphanized) {
                ret = add_pending_dir_move(sctx,
                                           sctx->cur_ino,
                                           sctx->cur_inode_gen,
                                           di_key.objectid,
                                           &sctx->new_refs,
                                           &sctx->deleted_refs,
                                           is_orphan);
                if (!ret)
                        ret = 1;
        }
out:
        btrfs_free_path(path);
        return ret;
}

/*
 * Check if ino ino1 is an ancestor of inode ino2 in the given root.
 * Return 1 if true, 0 if false and < 0 on error.
 */
static int is_ancestor(struct btrfs_root *root,
                       const u64 ino1,
                       const u64 ino1_gen,
                       const u64 ino2,
                       struct fs_path *fs_path)
{
        u64 ino = ino2;

        while (ino > BTRFS_FIRST_FREE_OBJECTID) {
                int ret;
                u64 parent;
                u64 parent_gen;

                fs_path_reset(fs_path);
                ret = get_first_ref(root, ino, &parent, &parent_gen, fs_path);
                if (ret < 0) {
                        if (ret == -ENOENT && ino == ino2)
                                ret = 0;
                        return ret;
                }
                if (parent == ino1)
                        return parent_gen == ino1_gen ? 1 : 0;
                ino = parent;
        }
        return 0;
}

static int wait_for_parent_move(struct send_ctx *sctx,
                                struct recorded_ref *parent_ref,
                                const bool is_orphan)
{
        int ret = 0;
        u64 ino = parent_ref->dir;
        u64 parent_ino_before, parent_ino_after;
        struct fs_path *path_before = NULL;
        struct fs_path *path_after = NULL;
        int len1, len2;

        path_after = fs_path_alloc();
        path_before = fs_path_alloc();
        if (!path_after || !path_before) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * Our current directory inode may not yet be renamed/moved because some
         * ancestor (immediate or not) has to be renamed/moved first. So find if
         * such ancestor exists and make sure our own rename/move happens after
         * that ancestor is processed to avoid path build infinite loops (done
         * at get_cur_path()).
         */
        while (ino > BTRFS_FIRST_FREE_OBJECTID) {
                if (is_waiting_for_move(sctx, ino)) {
                        /*
                         * If the current inode is an ancestor of ino in the
                         * parent root, we need to delay the rename of the
                         * current inode, otherwise don't delayed the rename
                         * because we can end up with a circular dependency
                         * of renames, resulting in some directories never
                         * getting the respective rename operations issued in
                         * the send stream or getting into infinite path build
                         * loops.
                         */
                        ret = is_ancestor(sctx->parent_root,
                                          sctx->cur_ino, sctx->cur_inode_gen,
                                          ino, path_before);
                        if (ret)
                                break;
                }

                fs_path_reset(path_before);
                fs_path_reset(path_after);

                ret = get_first_ref(sctx->send_root, ino, &parent_ino_after,
                                    NULL, path_after);
                if (ret < 0)
                        goto out;
                ret = get_first_ref(sctx->parent_root, ino, &parent_ino_before,
                                    NULL, path_before);
                if (ret < 0 && ret != -ENOENT) {
                        goto out;
                } else if (ret == -ENOENT) {
                        ret = 0;
                        break;
                }

                len1 = fs_path_len(path_before);
                len2 = fs_path_len(path_after);
                if (ino > sctx->cur_ino &&
                    (parent_ino_before != parent_ino_after || len1 != len2 ||
                     memcmp(path_before->start, path_after->start, len1))) {
                        ret = 1;
                        break;
                }
                ino = parent_ino_after;
        }

out:
        fs_path_free(path_before);
        fs_path_free(path_after);

        if (ret == 1) {
                ret = add_pending_dir_move(sctx,
                                           sctx->cur_ino,
                                           sctx->cur_inode_gen,
                                           ino,
                                           &sctx->new_refs,
                                           &sctx->deleted_refs,
                                           is_orphan);
                if (!ret)
                        ret = 1;
        }

        return ret;
}

/*
 * This does all the move/link/unlink/rmdir magic.
 */
static int process_recorded_refs(struct send_ctx *sctx, int *pending_move)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct recorded_ref *cur;
        struct recorded_ref *cur2;
        struct list_head check_dirs;
        struct fs_path *valid_path = NULL;
        u64 ow_inode = 0;
        u64 ow_gen;
        int did_overwrite = 0;
        int is_orphan = 0;
        u64 last_dir_ino_rm = 0;
        bool can_rename = true;

        btrfs_debug(fs_info, "process_recorded_refs %llu", sctx->cur_ino);

        /*
         * This should never happen as the root dir always has the same ref
         * which is always '..'
         */
        BUG_ON(sctx->cur_ino <= BTRFS_FIRST_FREE_OBJECTID);
        INIT_LIST_HEAD(&check_dirs);

        valid_path = fs_path_alloc();
        if (!valid_path) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * First, check if the first ref of the current inode was overwritten
         * before. If yes, we know that the current inode was already orphanized
         * and thus use the orphan name. If not, we can use get_cur_path to
         * get the path of the first ref as it would like while receiving at
         * this point in time.
         * New inodes are always orphan at the beginning, so force to use the
         * orphan name in this case.
         * The first ref is stored in valid_path and will be updated if it
         * gets moved around.
         */
        if (!sctx->cur_inode_new) {
                ret = did_overwrite_first_ref(sctx, sctx->cur_ino,
                                sctx->cur_inode_gen);
                if (ret < 0)
                        goto out;
                if (ret)
                        did_overwrite = 1;
        }
        if (sctx->cur_inode_new || did_overwrite) {
                ret = gen_unique_name(sctx, sctx->cur_ino,
                                sctx->cur_inode_gen, valid_path);
                if (ret < 0)
                        goto out;
                is_orphan = 1;
        } else {
                ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                valid_path);
                if (ret < 0)
                        goto out;
        }

        list_for_each_entry(cur, &sctx->new_refs, list) {
                /*
                 * We may have refs where the parent directory does not exist
                 * yet. This happens if the parent directories inum is higher
                 * the the current inum. To handle this case, we create the
                 * parent directory out of order. But we need to check if this
                 * did already happen before due to other refs in the same dir.
                 */
                ret = get_cur_inode_state(sctx, cur->dir, cur->dir_gen);
                if (ret < 0)
                        goto out;
                if (ret == inode_state_will_create) {
                        ret = 0;
                        /*
                         * First check if any of the current inodes refs did
                         * already create the dir.
                         */
                        list_for_each_entry(cur2, &sctx->new_refs, list) {
                                if (cur == cur2)
                                        break;
                                if (cur2->dir == cur->dir) {
                                        ret = 1;
                                        break;
                                }
                        }

                        /*
                         * If that did not happen, check if a previous inode
                         * did already create the dir.
                         */
                        if (!ret)
                                ret = did_create_dir(sctx, cur->dir);
                        if (ret < 0)
                                goto out;
                        if (!ret) {
                                ret = send_create_inode(sctx, cur->dir);
                                if (ret < 0)
                                        goto out;
                        }
                }

                /*
                 * Check if this new ref would overwrite the first ref of
                 * another unprocessed inode. If yes, orphanize the
                 * overwritten inode. If we find an overwritten ref that is
                 * not the first ref, simply unlink it.
                 */
                ret = will_overwrite_ref(sctx, cur->dir, cur->dir_gen,
                                cur->name, cur->name_len,
                                &ow_inode, &ow_gen);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = is_first_ref(sctx->parent_root,
                                           ow_inode, cur->dir, cur->name,
                                           cur->name_len);
                        if (ret < 0)
                                goto out;
                        if (ret) {
                                struct name_cache_entry *nce;
                                struct waiting_dir_move *wdm;

                                ret = orphanize_inode(sctx, ow_inode, ow_gen,
                                                cur->full_path);
                                if (ret < 0)
                                        goto out;

                                /*
                                 * If ow_inode has its rename operation delayed
                                 * make sure that its orphanized name is used in
                                 * the source path when performing its rename
                                 * operation.
                                 */
                                if (is_waiting_for_move(sctx, ow_inode)) {
                                        wdm = get_waiting_dir_move(sctx,
                                                                   ow_inode);
                                        ASSERT(wdm);
                                        wdm->orphanized = true;
                                }

                                /*
                                 * Make sure we clear our orphanized inode's
                                 * name from the name cache. This is because the
                                 * inode ow_inode might be an ancestor of some
                                 * other inode that will be orphanized as well
                                 * later and has an inode number greater than
                                 * sctx->send_progress. We need to prevent
                                 * future name lookups from using the old name
                                 * and get instead the orphan name.
                                 */
                                nce = name_cache_search(sctx, ow_inode, ow_gen);
                                if (nce) {
                                        name_cache_delete(sctx, nce);
                                        kfree(nce);
                                }

                                /*
                                 * ow_inode might currently be an ancestor of
                                 * cur_ino, therefore compute valid_path (the
                                 * current path of cur_ino) again because it
                                 * might contain the pre-orphanization name of
                                 * ow_inode, which is no longer valid.
                                 */
                                fs_path_reset(valid_path);
                                ret = get_cur_path(sctx, sctx->cur_ino,
                                           sctx->cur_inode_gen, valid_path);
                                if (ret < 0)
                                        goto out;
                        } else {
                                ret = send_unlink(sctx, cur->full_path);
                                if (ret < 0)
                                        goto out;
                        }
                }

                if (S_ISDIR(sctx->cur_inode_mode) && sctx->parent_root) {
                        ret = wait_for_dest_dir_move(sctx, cur, is_orphan);
                        if (ret < 0)
                                goto out;
                        if (ret == 1) {
                                can_rename = false;
                                *pending_move = 1;
                        }
                }

                if (S_ISDIR(sctx->cur_inode_mode) && sctx->parent_root &&
                    can_rename) {
                        ret = wait_for_parent_move(sctx, cur, is_orphan);
                        if (ret < 0)
                                goto out;
                        if (ret == 1) {
                                can_rename = false;
                                *pending_move = 1;
                        }
                }

                /*
                 * link/move the ref to the new place. If we have an orphan
                 * inode, move it and update valid_path. If not, link or move
                 * it depending on the inode mode.
                 */
                if (is_orphan && can_rename) {
                        ret = send_rename(sctx, valid_path, cur->full_path);
                        if (ret < 0)
                                goto out;
                        is_orphan = 0;
                        ret = fs_path_copy(valid_path, cur->full_path);
                        if (ret < 0)
                                goto out;
                } else if (can_rename) {
                        if (S_ISDIR(sctx->cur_inode_mode)) {
                                /*
                                 * Dirs can't be linked, so move it. For moved
                                 * dirs, we always have one new and one deleted
                                 * ref. The deleted ref is ignored later.
                                 */
                                ret = send_rename(sctx, valid_path,
                                                  cur->full_path);
                                if (!ret)
                                        ret = fs_path_copy(valid_path,
                                                           cur->full_path);
                                if (ret < 0)
                                        goto out;
                        } else {
                                ret = send_link(sctx, cur->full_path,
                                                valid_path);
                                if (ret < 0)
                                        goto out;
                        }
                }
                ret = dup_ref(cur, &check_dirs);
                if (ret < 0)
                        goto out;
        }

        if (S_ISDIR(sctx->cur_inode_mode) && sctx->cur_inode_deleted) {
                /*
                 * Check if we can already rmdir the directory. If not,
                 * orphanize it. For every dir item inside that gets deleted
                 * later, we do this check again and rmdir it then if possible.
                 * See the use of check_dirs for more details.
                 */
                ret = can_rmdir(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                sctx->cur_ino);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = send_rmdir(sctx, valid_path);
                        if (ret < 0)
                                goto out;
                } else if (!is_orphan) {
                        ret = orphanize_inode(sctx, sctx->cur_ino,
                                        sctx->cur_inode_gen, valid_path);
                        if (ret < 0)
                                goto out;
                        is_orphan = 1;
                }

                list_for_each_entry(cur, &sctx->deleted_refs, list) {
                        ret = dup_ref(cur, &check_dirs);
                        if (ret < 0)
                                goto out;
                }
        } else if (S_ISDIR(sctx->cur_inode_mode) &&
                   !list_empty(&sctx->deleted_refs)) {
                /*
                 * We have a moved dir. Add the old parent to check_dirs
                 */
                cur = list_entry(sctx->deleted_refs.next, struct recorded_ref,
                                list);
                ret = dup_ref(cur, &check_dirs);
                if (ret < 0)
                        goto out;
        } else if (!S_ISDIR(sctx->cur_inode_mode)) {
                /*
                 * We have a non dir inode. Go through all deleted refs and
                 * unlink them if they were not already overwritten by other
                 * inodes.
                 */
                list_for_each_entry(cur, &sctx->deleted_refs, list) {
                        ret = did_overwrite_ref(sctx, cur->dir, cur->dir_gen,
                                        sctx->cur_ino, sctx->cur_inode_gen,
                                        cur->name, cur->name_len);
                        if (ret < 0)
                                goto out;
                        if (!ret) {
                                ret = send_unlink(sctx, cur->full_path);
                                if (ret < 0)
                                        goto out;
                        }
                        ret = dup_ref(cur, &check_dirs);
                        if (ret < 0)
                                goto out;
                }
                /*
                 * If the inode is still orphan, unlink the orphan. This may
                 * happen when a previous inode did overwrite the first ref
                 * of this inode and no new refs were added for the current
                 * inode. Unlinking does not mean that the inode is deleted in
                 * all cases. There may still be links to this inode in other
                 * places.
                 */
                if (is_orphan) {
                        ret = send_unlink(sctx, valid_path);
                        if (ret < 0)
                                goto out;
                }
        }

        /*
         * We did collect all parent dirs where cur_inode was once located. We
         * now go through all these dirs and check if they are pending for
         * deletion and if it's finally possible to perform the rmdir now.
         * We also update the inode stats of the parent dirs here.
         */
        list_for_each_entry(cur, &check_dirs, list) {
                /*
                 * In case we had refs into dirs that were not processed yet,
                 * we don't need to do the utime and rmdir logic for these dirs.
                 * The dir will be processed later.
                 */
                if (cur->dir > sctx->cur_ino)
                        continue;

                ret = get_cur_inode_state(sctx, cur->dir, cur->dir_gen);
                if (ret < 0)
                        goto out;

                if (ret == inode_state_did_create ||
                    ret == inode_state_no_change) {
                        /* TODO delayed utimes */
                        ret = send_utimes(sctx, cur->dir, cur->dir_gen);
                        if (ret < 0)
                                goto out;
                } else if (ret == inode_state_did_delete &&
                           cur->dir != last_dir_ino_rm) {
                        ret = can_rmdir(sctx, cur->dir, cur->dir_gen,
                                        sctx->cur_ino);
                        if (ret < 0)
                                goto out;
                        if (ret) {
                                ret = get_cur_path(sctx, cur->dir,
                                                   cur->dir_gen, valid_path);
                                if (ret < 0)
                                        goto out;
                                ret = send_rmdir(sctx, valid_path);
                                if (ret < 0)
                                        goto out;
                                last_dir_ino_rm = cur->dir;
                        }
                }
        }

        ret = 0;

out:
        __free_recorded_refs(&check_dirs);
        free_recorded_refs(sctx);
        fs_path_free(valid_path);
        return ret;
}

static int record_ref(struct btrfs_root *root, int num, u64 dir, int index,
                      struct fs_path *name, void *ctx, struct list_head *refs)
{
        int ret = 0;
        struct send_ctx *sctx = ctx;
        struct fs_path *p;
        u64 gen;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = get_inode_info(root, dir, NULL, &gen, NULL, NULL,
                        NULL, NULL);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, dir, gen, p);
        if (ret < 0)
                goto out;
        ret = fs_path_add_path(p, name);
        if (ret < 0)
                goto out;

        ret = __record_ref(refs, dir, gen, p);

out:
        if (ret)
                fs_path_free(p);
        return ret;
}

static int __record_new_ref(int num, u64 dir, int index,
                            struct fs_path *name,
                            void *ctx)
{
        struct send_ctx *sctx = ctx;
        return record_ref(sctx->send_root, num, dir, index, name,
                          ctx, &sctx->new_refs);
}


static int __record_deleted_ref(int num, u64 dir, int index,
                                struct fs_path *name,
                                void *ctx)
{
        struct send_ctx *sctx = ctx;
        return record_ref(sctx->parent_root, num, dir, index, name,
                          ctx, &sctx->deleted_refs);
}

static int record_new_ref(struct send_ctx *sctx)
{
        int ret;

        ret = iterate_inode_ref(sctx->send_root, sctx->left_path,
                                sctx->cmp_key, 0, __record_new_ref, sctx);
        if (ret < 0)
                goto out;
        ret = 0;

out:
        return ret;
}

static int record_deleted_ref(struct send_ctx *sctx)
{
        int ret;

        ret = iterate_inode_ref(sctx->parent_root, sctx->right_path,
                                sctx->cmp_key, 0, __record_deleted_ref, sctx);
        if (ret < 0)
                goto out;
        ret = 0;

out:
        return ret;
}

struct find_ref_ctx {
        u64 dir;
        u64 dir_gen;
        struct btrfs_root *root;
        struct fs_path *name;
        int found_idx;
};

static int __find_iref(int num, u64 dir, int index,
                       struct fs_path *name,
                       void *ctx_)
{
        struct find_ref_ctx *ctx = ctx_;
        u64 dir_gen;
        int ret;

        if (dir == ctx->dir && fs_path_len(name) == fs_path_len(ctx->name) &&
            strncmp(name->start, ctx->name->start, fs_path_len(name)) == 0) {
                /*
                 * To avoid doing extra lookups we'll only do this if everything
                 * else matches.
                 */
                ret = get_inode_info(ctx->root, dir, NULL, &dir_gen, NULL,
                                     NULL, NULL, NULL);
                if (ret)
                        return ret;
                if (dir_gen != ctx->dir_gen)
                        return 0;
                ctx->found_idx = num;
                return 1;
        }
        return 0;
}

static int find_iref(struct btrfs_root *root,
                     struct btrfs_path *path,
                     struct btrfs_key *key,
                     u64 dir, u64 dir_gen, struct fs_path *name)
{
        int ret;
        struct find_ref_ctx ctx;

        ctx.dir = dir;
        ctx.name = name;
        ctx.dir_gen = dir_gen;
        ctx.found_idx = -1;
        ctx.root = root;

        ret = iterate_inode_ref(root, path, key, 0, __find_iref, &ctx);
        if (ret < 0)
                return ret;

        if (ctx.found_idx == -1)
                return -ENOENT;

        return ctx.found_idx;
}

static int __record_changed_new_ref(int num, u64 dir, int index,
                                    struct fs_path *name,
                                    void *ctx)
{
        u64 dir_gen;
        int ret;
        struct send_ctx *sctx = ctx;

        ret = get_inode_info(sctx->send_root, dir, NULL, &dir_gen, NULL,
                             NULL, NULL, NULL);
        if (ret)
                return ret;

        ret = find_iref(sctx->parent_root, sctx->right_path,
                        sctx->cmp_key, dir, dir_gen, name);
        if (ret == -ENOENT)
                ret = __record_new_ref(num, dir, index, name, sctx);
        else if (ret > 0)
                ret = 0;

        return ret;
}

static int __record_changed_deleted_ref(int num, u64 dir, int index,
                                        struct fs_path *name,
                                        void *ctx)
{
        u64 dir_gen;
        int ret;
        struct send_ctx *sctx = ctx;

        ret = get_inode_info(sctx->parent_root, dir, NULL, &dir_gen, NULL,
                             NULL, NULL, NULL);
        if (ret)
                return ret;

        ret = find_iref(sctx->send_root, sctx->left_path, sctx->cmp_key,
                        dir, dir_gen, name);
        if (ret == -ENOENT)
                ret = __record_deleted_ref(num, dir, index, name, sctx);
        else if (ret > 0)
                ret = 0;

        return ret;
}

static int record_changed_ref(struct send_ctx *sctx)
{
        int ret = 0;

        ret = iterate_inode_ref(sctx->send_root, sctx->left_path,
                        sctx->cmp_key, 0, __record_changed_new_ref, sctx);
        if (ret < 0)
                goto out;
        ret = iterate_inode_ref(sctx->parent_root, sctx->right_path,
                        sctx->cmp_key, 0, __record_changed_deleted_ref, sctx);
        if (ret < 0)
                goto out;
        ret = 0;

out:
        return ret;
}

/*
 * Record and process all refs at once. Needed when an inode changes the
 * generation number, which means that it was deleted and recreated.
 */
static int process_all_refs(struct send_ctx *sctx,
                            enum btrfs_compare_tree_result cmd)
{
        int ret;
        struct btrfs_root *root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct extent_buffer *eb;
        int slot;
        iterate_inode_ref_t cb;
        int pending_move = 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        if (cmd == BTRFS_COMPARE_TREE_NEW) {
                root = sctx->send_root;
                cb = __record_new_ref;
        } else if (cmd == BTRFS_COMPARE_TREE_DELETED) {
                root = sctx->parent_root;
                cb = __record_deleted_ref;
        } else {
                btrfs_err(sctx->send_root->fs_info,
                                "Wrong command %d in process_all_refs", cmd);
                ret = -EINVAL;
                goto out;
        }

        key.objectid = sctx->cmp_key->objectid;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                eb = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(eb)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto out;
                        else if (ret > 0)
                                break;
                        continue;
                }

                btrfs_item_key_to_cpu(eb, &found_key, slot);

                if (found_key.objectid != key.objectid ||
                    (found_key.type != BTRFS_INODE_REF_KEY &&
                     found_key.type != BTRFS_INODE_EXTREF_KEY))
                        break;

                ret = iterate_inode_ref(root, path, &found_key, 0, cb, sctx);
                if (ret < 0)
                        goto out;

                path->slots[0]++;
        }
        btrfs_release_path(path);

        /*
         * We don't actually care about pending_move as we are simply
         * re-creating this inode and will be rename'ing it into place once we
         * rename the parent directory.
         */
        ret = process_recorded_refs(sctx, &pending_move);
out:
        btrfs_free_path(path);
        return ret;
}

static int send_set_xattr(struct send_ctx *sctx,
                          struct fs_path *path,
                          const char *name, int name_len,
                          const char *data, int data_len)
{
        int ret = 0;

        ret = begin_cmd(sctx, BTRFS_SEND_C_SET_XATTR);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_STRING(sctx, BTRFS_SEND_A_XATTR_NAME, name, name_len);
        TLV_PUT(sctx, BTRFS_SEND_A_XATTR_DATA, data, data_len);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        return ret;
}

static int send_remove_xattr(struct send_ctx *sctx,
                          struct fs_path *path,
                          const char *name, int name_len)
{
        int ret = 0;

        ret = begin_cmd(sctx, BTRFS_SEND_C_REMOVE_XATTR);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_STRING(sctx, BTRFS_SEND_A_XATTR_NAME, name, name_len);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        return ret;
}

static int __process_new_xattr(int num, struct btrfs_key *di_key,
                               const char *name, int name_len,
                               const char *data, int data_len,
                               u8 type, void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;
        struct fs_path *p;
        struct posix_acl_xattr_header dummy_acl;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        /*
         * This hack is needed because empty acls are stored as zero byte
         * data in xattrs. Problem with that is, that receiving these zero byte
         * acls will fail later. To fix this, we send a dummy acl list that
         * only contains the version number and no entries.
         */
        if (!strncmp(name, XATTR_NAME_POSIX_ACL_ACCESS, name_len) ||
            !strncmp(name, XATTR_NAME_POSIX_ACL_DEFAULT, name_len)) {
                if (data_len == 0) {
                        dummy_acl.a_version =
                                        cpu_to_le32(POSIX_ACL_XATTR_VERSION);
                        data = (char *)&dummy_acl;
                        data_len = sizeof(dummy_acl);
                }
        }

        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
        if (ret < 0)
                goto out;

        ret = send_set_xattr(sctx, p, name, name_len, data, data_len);

out:
        fs_path_free(p);
        return ret;
}

static int __process_deleted_xattr(int num, struct btrfs_key *di_key,
                                   const char *name, int name_len,
                                   const char *data, int data_len,
                                   u8 type, void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;
        struct fs_path *p;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
        if (ret < 0)
                goto out;

        ret = send_remove_xattr(sctx, p, name, name_len);

out:
        fs_path_free(p);
        return ret;
}

static int process_new_xattr(struct send_ctx *sctx)
{
        int ret = 0;

        ret = iterate_dir_item(sctx->send_root, sctx->left_path,
                               sctx->cmp_key, __process_new_xattr, sctx);

        return ret;
}

static int process_deleted_xattr(struct send_ctx *sctx)
{
        return iterate_dir_item(sctx->parent_root, sctx->right_path,
                                sctx->cmp_key, __process_deleted_xattr, sctx);
}

struct find_xattr_ctx {
        const char *name;
        int name_len;
        int found_idx;
        char *found_data;
        int found_data_len;
};

static int __find_xattr(int num, struct btrfs_key *di_key,
                        const char *name, int name_len,
                        const char *data, int data_len,
                        u8 type, void *vctx)
{
        struct find_xattr_ctx *ctx = vctx;

        if (name_len == ctx->name_len &&
            strncmp(name, ctx->name, name_len) == 0) {
                ctx->found_idx = num;
                ctx->found_data_len = data_len;
                ctx->found_data = kmemdup(data, data_len, GFP_KERNEL);
                if (!ctx->found_data)
                        return -ENOMEM;
                return 1;
        }
        return 0;
}

static int find_xattr(struct btrfs_root *root,
                      struct btrfs_path *path,
                      struct btrfs_key *key,
                      const char *name, int name_len,
                      char **data, int *data_len)
{
        int ret;
        struct find_xattr_ctx ctx;

        ctx.name = name;
        ctx.name_len = name_len;
        ctx.found_idx = -1;
        ctx.found_data = NULL;
        ctx.found_data_len = 0;

        ret = iterate_dir_item(root, path, key, __find_xattr, &ctx);
        if (ret < 0)
                return ret;

        if (ctx.found_idx == -1)
                return -ENOENT;
        if (data) {
                *data = ctx.found_data;
                *data_len = ctx.found_data_len;
        } else {
                kfree(ctx.found_data);
        }
        return ctx.found_idx;
}


static int __process_changed_new_xattr(int num, struct btrfs_key *di_key,
                                       const char *name, int name_len,
                                       const char *data, int data_len,
                                       u8 type, void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;
        char *found_data = NULL;
        int found_data_len  = 0;

        ret = find_xattr(sctx->parent_root, sctx->right_path,
                         sctx->cmp_key, name, name_len, &found_data,
                         &found_data_len);
        if (ret == -ENOENT) {
                ret = __process_new_xattr(num, di_key, name, name_len, data,
                                data_len, type, ctx);
        } else if (ret >= 0) {
                if (data_len != found_data_len ||
                    memcmp(data, found_data, data_len)) {
                        ret = __process_new_xattr(num, di_key, name, name_len,
                                        data, data_len, type, ctx);
                } else {
                        ret = 0;
                }
        }

        kfree(found_data);
        return ret;
}

static int __process_changed_deleted_xattr(int num, struct btrfs_key *di_key,
                                           const char *name, int name_len,
                                           const char *data, int data_len,
                                           u8 type, void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;

        ret = find_xattr(sctx->send_root, sctx->left_path, sctx->cmp_key,
                         name, name_len, NULL, NULL);
        if (ret == -ENOENT)
                ret = __process_deleted_xattr(num, di_key, name, name_len, data,
                                data_len, type, ctx);
        else if (ret >= 0)
                ret = 0;

        return ret;
}

static int process_changed_xattr(struct send_ctx *sctx)
{
        int ret = 0;

        ret = iterate_dir_item(sctx->send_root, sctx->left_path,
                        sctx->cmp_key, __process_changed_new_xattr, sctx);
        if (ret < 0)
                goto out;
        ret = iterate_dir_item(sctx->parent_root, sctx->right_path,
                        sctx->cmp_key, __process_changed_deleted_xattr, sctx);

out:
        return ret;
}

static int process_all_new_xattrs(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_root *root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct extent_buffer *eb;
        int slot;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        root = sctx->send_root;

        key.objectid = sctx->cmp_key->objectid;
        key.type = BTRFS_XATTR_ITEM_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                eb = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(eb)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0) {
                                goto out;
                        } else if (ret > 0) {
                                ret = 0;
                                break;
                        }
                        continue;
                }

                btrfs_item_key_to_cpu(eb, &found_key, slot);
                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        ret = 0;
                        goto out;
                }

                ret = iterate_dir_item(root, path, &found_key,
                                       __process_new_xattr, sctx);
                if (ret < 0)
                        goto out;

                path->slots[0]++;
        }

out:
        btrfs_free_path(path);
        return ret;
}

static ssize_t fill_read_buf(struct send_ctx *sctx, u64 offset, u32 len)
{
        struct btrfs_root *root = sctx->send_root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct inode *inode;
        struct page *page;
        char *addr;
        struct btrfs_key key;
        pgoff_t index = offset >> PAGE_SHIFT;
        pgoff_t last_index;
        unsigned pg_offset = offset & ~PAGE_MASK;
        ssize_t ret = 0;

        key.objectid = sctx->cur_ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        inode = btrfs_iget(fs_info->sb, &key, root, NULL);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        if (offset + len > i_size_read(inode)) {
                if (offset > i_size_read(inode))
                        len = 0;
                else
                        len = offset - i_size_read(inode);
        }
        if (len == 0)
                goto out;

        last_index = (offset + len - 1) >> PAGE_SHIFT;

        /* initial readahead */
        memset(&sctx->ra, 0, sizeof(struct file_ra_state));
        file_ra_state_init(&sctx->ra, inode->i_mapping);
        btrfs_force_ra(inode->i_mapping, &sctx->ra, NULL, index,
                       last_index - index + 1);

        while (index <= last_index) {
                unsigned cur_len = min_t(unsigned, len,
                                         PAGE_SIZE - pg_offset);
                page = find_or_create_page(inode->i_mapping, index, GFP_KERNEL);
                if (!page) {
                        ret = -ENOMEM;
                        break;
                }

                if (!PageUptodate(page)) {
                        btrfs_readpage(NULL, page);
                        lock_page(page);
                        if (!PageUptodate(page)) {
                                unlock_page(page);
                                put_page(page);
                                ret = -EIO;
                                break;
                        }
                }

                addr = kmap(page);
                memcpy(sctx->read_buf + ret, addr + pg_offset, cur_len);
                kunmap(page);
                unlock_page(page);
                put_page(page);
                index++;
                pg_offset = 0;
                len -= cur_len;
                ret += cur_len;
        }
out:
        iput(inode);
        return ret;
}

/*
 * Read some bytes from the current inode/file and send a write command to
 * user space.
 */
static int send_write(struct send_ctx *sctx, u64 offset, u32 len)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct fs_path *p;
        ssize_t num_read = 0;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        btrfs_debug(fs_info, "send_write offset=%llu, len=%d", offset, len);

        num_read = fill_read_buf(sctx, offset, len);
        if (num_read <= 0) {
                if (num_read < 0)
                        ret = num_read;
                goto out;
        }

        ret = begin_cmd(sctx, BTRFS_SEND_C_WRITE);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT(sctx, BTRFS_SEND_A_DATA, sctx->read_buf, num_read);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        if (ret < 0)
                return ret;
        return num_read;
}

/*
 * Send a clone command to user space.
 */
static int send_clone(struct send_ctx *sctx,
                      u64 offset, u32 len,
                      struct clone_root *clone_root)
{
        int ret = 0;
        struct fs_path *p;
        u64 gen;

        btrfs_debug(sctx->send_root->fs_info,
                    "send_clone offset=%llu, len=%d, clone_root=%llu, clone_inode=%llu, clone_offset=%llu",
                    offset, len, clone_root->root->objectid, clone_root->ino,
                    clone_root->offset);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = begin_cmd(sctx, BTRFS_SEND_C_CLONE);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
        if (ret < 0)
                goto out;

        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_LEN, len);
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);

        if (clone_root->root == sctx->send_root) {
                ret = get_inode_info(sctx->send_root, clone_root->ino, NULL,
                                &gen, NULL, NULL, NULL, NULL);
                if (ret < 0)
                        goto out;
                ret = get_cur_path(sctx, clone_root->ino, gen, p);
        } else {
                ret = get_inode_path(clone_root->root, clone_root->ino, p);
        }
        if (ret < 0)
                goto out;

        /*
         * If the parent we're using has a received_uuid set then use that as
         * our clone source as that is what we will look for when doing a
         * receive.
         *
         * This covers the case that we create a snapshot off of a received
         * subvolume and then use that as the parent and try to receive on a
         * different host.
         */
        if (!btrfs_is_empty_uuid(clone_root->root->root_item.received_uuid))
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                             clone_root->root->root_item.received_uuid);
        else
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                             clone_root->root->root_item.uuid);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                    le64_to_cpu(clone_root->root->root_item.ctransid));
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_CLONE_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_OFFSET,
                        clone_root->offset);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

/*
 * Send an update extent command to user space.
 */
static int send_update_extent(struct send_ctx *sctx,
                              u64 offset, u32 len)
{
        int ret = 0;
        struct fs_path *p;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = begin_cmd(sctx, BTRFS_SEND_C_UPDATE_EXTENT);
        if (ret < 0)
                goto out;

        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, len);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

static int send_hole(struct send_ctx *sctx, u64 end)
{
        struct fs_path *p = NULL;
        u64 offset = sctx->cur_inode_last_extent;
        u64 len;
        int ret = 0;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;
        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
        if (ret < 0)
                goto tlv_put_failure;
        memset(sctx->read_buf, 0, BTRFS_SEND_READ_SIZE);
        while (offset < end) {
                len = min_t(u64, end - offset, BTRFS_SEND_READ_SIZE);

                ret = begin_cmd(sctx, BTRFS_SEND_C_WRITE);
                if (ret < 0)
                        break;
                TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
                TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
                TLV_PUT(sctx, BTRFS_SEND_A_DATA, sctx->read_buf, len);
                ret = send_cmd(sctx);
                if (ret < 0)
                        break;
                offset += len;
        }
tlv_put_failure:
        fs_path_free(p);
        return ret;
}

static int send_extent_data(struct send_ctx *sctx,
                            const u64 offset,
                            const u64 len)
{
        u64 sent = 0;

        if (sctx->flags & BTRFS_SEND_FLAG_NO_FILE_DATA)
                return send_update_extent(sctx, offset, len);

        while (sent < len) {
                u64 size = len - sent;
                int ret;

                if (size > BTRFS_SEND_READ_SIZE)
                        size = BTRFS_SEND_READ_SIZE;
                ret = send_write(sctx, offset + sent, size);
                if (ret < 0)
                        return ret;
                if (!ret)
                        break;
                sent += ret;
        }
        return 0;
}

static int clone_range(struct send_ctx *sctx,
                       struct clone_root *clone_root,
                       const u64 disk_byte,
                       u64 data_offset,
                       u64 offset,
                       u64 len)
{
        struct btrfs_path *path;
        struct btrfs_key key;
        int ret;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        /*
         * We can't send a clone operation for the entire range if we find
         * extent items in the respective range in the source file that
         * refer to different extents or if we find holes.
         * So check for that and do a mix of clone and regular write/copy
         * operations if needed.
         *
         * Example:
         *
         * mkfs.btrfs -f /dev/sda
         * mount /dev/sda /mnt
         * xfs_io -f -c "pwrite -S 0xaa 0K 100K" /mnt/foo
         * cp --reflink=always /mnt/foo /mnt/bar
         * xfs_io -c "pwrite -S 0xbb 50K 50K" /mnt/foo
         * btrfs subvolume snapshot -r /mnt /mnt/snap
         *
         * If when we send the snapshot and we are processing file bar (which
         * has a higher inode number than foo) we blindly send a clone operation
         * for the [0, 100K[ range from foo to bar, the receiver ends up getting
         * a file bar that matches the content of file foo - iow, doesn't match
         * the content from bar in the original filesystem.
         */
        key.objectid = clone_root->ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = clone_root->offset;
        ret = btrfs_search_slot(NULL, clone_root->root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        if (ret > 0 && path->slots[0] > 0) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
                if (key.objectid == clone_root->ino &&
                    key.type == BTRFS_EXTENT_DATA_KEY)
                        path->slots[0]--;
        }

        while (true) {
                struct extent_buffer *leaf = path->nodes[0];
                int slot = path->slots[0];
                struct btrfs_file_extent_item *ei;
                u8 type;
                u64 ext_len;
                u64 clone_len;

                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(clone_root->root, path);
                        if (ret < 0)
                                goto out;
                        else if (ret > 0)
                                break;
                        continue;
                }

                btrfs_item_key_to_cpu(leaf, &key, slot);

                /*
                 * We might have an implicit trailing hole (NO_HOLES feature
                 * enabled). We deal with it after leaving this loop.
                 */
                if (key.objectid != clone_root->ino ||
                    key.type != BTRFS_EXTENT_DATA_KEY)
                        break;

                ei = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
                type = btrfs_file_extent_type(leaf, ei);
                if (type == BTRFS_FILE_EXTENT_INLINE) {
                        ext_len = btrfs_file_extent_inline_len(leaf, slot, ei);
                        ext_len = PAGE_ALIGN(ext_len);
                } else {
                        ext_len = btrfs_file_extent_num_bytes(leaf, ei);
                }

                if (key.offset + ext_len <= clone_root->offset)
                        goto next;

                if (key.offset > clone_root->offset) {
                        /* Implicit hole, NO_HOLES feature enabled. */
                        u64 hole_len = key.offset - clone_root->offset;

                        if (hole_len > len)
                                hole_len = len;
                        ret = send_extent_data(sctx, offset, hole_len);
                        if (ret < 0)
                                goto out;

                        len -= hole_len;
                        if (len == 0)
                                break;
                        offset += hole_len;
                        clone_root->offset += hole_len;
                        data_offset += hole_len;
                }

                if (key.offset >= clone_root->offset + len)
                        break;

                clone_len = min_t(u64, ext_len, len);

                if (btrfs_file_extent_disk_bytenr(leaf, ei) == disk_byte &&
                    btrfs_file_extent_offset(leaf, ei) == data_offset)
                        ret = send_clone(sctx, offset, clone_len, clone_root);
                else
                        ret = send_extent_data(sctx, offset, clone_len);

                if (ret < 0)
                        goto out;

                len -= clone_len;
                if (len == 0)
                        break;
                offset += clone_len;
                clone_root->offset += clone_len;
                data_offset += clone_len;
next:
                path->slots[0]++;
        }

        if (len > 0)
                ret = send_extent_data(sctx, offset, len);
        else
                ret = 0;
out:
        btrfs_free_path(path);
        return ret;
}

static int send_write_or_clone(struct send_ctx *sctx,
                               struct btrfs_path *path,
                               struct btrfs_key *key,
                               struct clone_root *clone_root)
{
        int ret = 0;
        struct btrfs_file_extent_item *ei;
        u64 offset = key->offset;
        u64 len;
        u8 type;
        u64 bs = sctx->send_root->fs_info->sb->s_blocksize;

        ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                        struct btrfs_file_extent_item);
        type = btrfs_file_extent_type(path->nodes[0], ei);
        if (type == BTRFS_FILE_EXTENT_INLINE) {
                len = btrfs_file_extent_inline_len(path->nodes[0],
                                                   path->slots[0], ei);
                /*
                 * it is possible the inline item won't cover the whole page,
                 * but there may be items after this page.  Make
                 * sure to send the whole thing
                 */
                len = PAGE_ALIGN(len);
        } else {
                len = btrfs_file_extent_num_bytes(path->nodes[0], ei);
        }

        if (offset + len > sctx->cur_inode_size)
                len = sctx->cur_inode_size - offset;
        if (len == 0) {
                ret = 0;
                goto out;
        }

        if (clone_root && IS_ALIGNED(offset + len, bs)) {
                u64 disk_byte;
                u64 data_offset;

                disk_byte = btrfs_file_extent_disk_bytenr(path->nodes[0], ei);
                data_offset = btrfs_file_extent_offset(path->nodes[0], ei);
                ret = clone_range(sctx, clone_root, disk_byte, data_offset,
                                  offset, len);
        } else {
                ret = send_extent_data(sctx, offset, len);
        }
out:
        return ret;
}

static int is_extent_unchanged(struct send_ctx *sctx,
                               struct btrfs_path *left_path,
                               struct btrfs_key *ekey)
{
        int ret = 0;
        struct btrfs_key key;
        struct btrfs_path *path = NULL;
        struct extent_buffer *eb;
        int slot;
        struct btrfs_key found_key;
        struct btrfs_file_extent_item *ei;
        u64 left_disknr;
        u64 right_disknr;
        u64 left_offset;
        u64 right_offset;
        u64 left_offset_fixed;
        u64 left_len;
        u64 right_len;
        u64 left_gen;
        u64 right_gen;
        u8 left_type;
        u8 right_type;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        eb = left_path->nodes[0];
        slot = left_path->slots[0];
        ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
        left_type = btrfs_file_extent_type(eb, ei);

        if (left_type != BTRFS_FILE_EXTENT_REG) {
                ret = 0;
                goto out;
        }
        left_disknr = btrfs_file_extent_disk_bytenr(eb, ei);
        left_len = btrfs_file_extent_num_bytes(eb, ei);
        left_offset = btrfs_file_extent_offset(eb, ei);
        left_gen = btrfs_file_extent_generation(eb, ei);

        /*
         * Following comments will refer to these graphics. L is the left
         * extents which we are checking at the moment. 1-8 are the right
         * extents that we iterate.
         *
         *       |-----L-----|
         * |-1-|-2a-|-3-|-4-|-5-|-6-|
         *
         *       |-----L-----|
         * |--1--|-2b-|...(same as above)
         *
         * Alternative situation. Happens on files where extents got split.
         *       |-----L-----|
         * |-----------7-----------|-6-|
         *
         * Alternative situation. Happens on files which got larger.
         *       |-----L-----|
         * |-8-|
         * Nothing follows after 8.
         */

        key.objectid = ekey->objectid;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = ekey->offset;
        ret = btrfs_search_slot_for_read(sctx->parent_root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        if (ret) {
                ret = 0;
                goto out;
        }

        /*
         * Handle special case where the right side has no extents at all.
         */
        eb = path->nodes[0];
        slot = path->slots[0];
        btrfs_item_key_to_cpu(eb, &found_key, slot);
        if (found_key.objectid != key.objectid ||
            found_key.type != key.type) {
                /* If we're a hole then just pretend nothing changed */
                ret = (left_disknr) ? 0 : 1;
                goto out;
        }

        /*
         * We're now on 2a, 2b or 7.
         */
        key = found_key;
        while (key.offset < ekey->offset + left_len) {
                ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
                right_type = btrfs_file_extent_type(eb, ei);
                if (right_type != BTRFS_FILE_EXTENT_REG) {
                        ret = 0;
                        goto out;
                }

                right_disknr = btrfs_file_extent_disk_bytenr(eb, ei);
                right_len = btrfs_file_extent_num_bytes(eb, ei);
                right_offset = btrfs_file_extent_offset(eb, ei);
                right_gen = btrfs_file_extent_generation(eb, ei);

                /*
                 * Are we at extent 8? If yes, we know the extent is changed.
                 * This may only happen on the first iteration.
                 */
                if (found_key.offset + right_len <= ekey->offset) {
                        /* If we're a hole just pretend nothing changed */
                        ret = (left_disknr) ? 0 : 1;
                        goto out;
                }

                left_offset_fixed = left_offset;
                if (key.offset < ekey->offset) {
                        /* Fix the right offset for 2a and 7. */
                        right_offset += ekey->offset - key.offset;
                } else {
                        /* Fix the left offset for all behind 2a and 2b */
                        left_offset_fixed += key.offset - ekey->offset;
                }

                /*
                 * Check if we have the same extent.
                 */
                if (left_disknr != right_disknr ||
                    left_offset_fixed != right_offset ||
                    left_gen != right_gen) {
                        ret = 0;
                        goto out;
                }

                /*
                 * Go to the next extent.
                 */
                ret = btrfs_next_item(sctx->parent_root, path);
                if (ret < 0)
                        goto out;
                if (!ret) {
                        eb = path->nodes[0];
                        slot = path->slots[0];
                        btrfs_item_key_to_cpu(eb, &found_key, slot);
                }
                if (ret || found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        key.offset += right_len;
                        break;
                }
                if (found_key.offset != key.offset + right_len) {
                        ret = 0;
                        goto out;
                }
                key = found_key;
        }

        /*
         * We're now behind the left extent (treat as unchanged) or at the end
         * of the right side (treat as changed).
         */
        if (key.offset >= ekey->offset + left_len)
                ret = 1;
        else
                ret = 0;


out:
        btrfs_free_path(path);
        return ret;
}

static int get_last_extent(struct send_ctx *sctx, u64 offset)
{
        struct btrfs_path *path;
        struct btrfs_root *root = sctx->send_root;
        struct btrfs_file_extent_item *fi;
        struct btrfs_key key;
        u64 extent_end;
        u8 type;
        int ret;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        sctx->cur_inode_last_extent = 0;

        key.objectid = sctx->cur_ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = offset;
        ret = btrfs_search_slot_for_read(root, &key, path, 0, 1);
        if (ret < 0)
                goto out;
        ret = 0;
        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        if (key.objectid != sctx->cur_ino || key.type != BTRFS_EXTENT_DATA_KEY)
                goto out;

        fi = btrfs_item_ptr(path->nodes[0], path->slots[0],
                            struct btrfs_file_extent_item);
        type = btrfs_file_extent_type(path->nodes[0], fi);
        if (type == BTRFS_FILE_EXTENT_INLINE) {
                u64 size = btrfs_file_extent_inline_len(path->nodes[0],
                                                        path->slots[0], fi);
                extent_end = ALIGN(key.offset + size,
                                   sctx->send_root->fs_info->sectorsize);
        } else {
                extent_end = key.offset +
                        btrfs_file_extent_num_bytes(path->nodes[0], fi);
        }
        sctx->cur_inode_last_extent = extent_end;
out:
        btrfs_free_path(path);
        return ret;
}

static int maybe_send_hole(struct send_ctx *sctx, struct btrfs_path *path,
                           struct btrfs_key *key)
{
        struct btrfs_file_extent_item *fi;
        u64 extent_end;
        u8 type;
        int ret = 0;

        if (sctx->cur_ino != key->objectid || !need_send_hole(sctx))
                return 0;

        if (sctx->cur_inode_last_extent == (u64)-1) {
                ret = get_last_extent(sctx, key->offset - 1);
                if (ret)
                        return ret;
        }

        fi = btrfs_item_ptr(path->nodes[0], path->slots[0],
                            struct btrfs_file_extent_item);
        type = btrfs_file_extent_type(path->nodes[0], fi);
        if (type == BTRFS_FILE_EXTENT_INLINE) {
                u64 size = btrfs_file_extent_inline_len(path->nodes[0],
                                                        path->slots[0], fi);
                extent_end = ALIGN(key->offset + size,
                                   sctx->send_root->fs_info->sectorsize);
        } else {
                extent_end = key->offset +
                        btrfs_file_extent_num_bytes(path->nodes[0], fi);
        }

        if (path->slots[0] == 0 &&
            sctx->cur_inode_last_extent < key->offset) {
                /*
                 * We might have skipped entire leafs that contained only
                 * file extent items for our current inode. These leafs have
                 * a generation number smaller (older) than the one in the
                 * current leaf and the leaf our last extent came from, and
                 * are located between these 2 leafs.
                 */
                ret = get_last_extent(sctx, key->offset - 1);
                if (ret)
                        return ret;
        }

        if (sctx->cur_inode_last_extent < key->offset)
                ret = send_hole(sctx, key->offset);
        sctx->cur_inode_last_extent = extent_end;
        return ret;
}

static int process_extent(struct send_ctx *sctx,
                          struct btrfs_path *path,
                          struct btrfs_key *key)
{
        struct clone_root *found_clone = NULL;
        int ret = 0;

        if (S_ISLNK(sctx->cur_inode_mode))
                return 0;

        if (sctx->parent_root && !sctx->cur_inode_new) {
                ret = is_extent_unchanged(sctx, path, key);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = 0;
                        goto out_hole;
                }
        } else {
                struct btrfs_file_extent_item *ei;
                u8 type;

                ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                    struct btrfs_file_extent_item);
                type = btrfs_file_extent_type(path->nodes[0], ei);
                if (type == BTRFS_FILE_EXTENT_PREALLOC ||
                    type == BTRFS_FILE_EXTENT_REG) {
                        /*
                         * The send spec does not have a prealloc command yet,
                         * so just leave a hole for prealloc'ed extents until
                         * we have enough commands queued up to justify rev'ing
                         * the send spec.
                         */
                        if (type == BTRFS_FILE_EXTENT_PREALLOC) {
                                ret = 0;
                                goto out;
                        }

                        /* Have a hole, just skip it. */
                        if (btrfs_file_extent_disk_bytenr(path->nodes[0], ei) == 0) {
                                ret = 0;
                                goto out;
                        }
                }
        }

        ret = find_extent_clone(sctx, path, key->objectid, key->offset,
                        sctx->cur_inode_size, &found_clone);
        if (ret != -ENOENT && ret < 0)
                goto out;

        ret = send_write_or_clone(sctx, path, key, found_clone);
        if (ret)
                goto out;
out_hole:
        ret = maybe_send_hole(sctx, path, key);
out:
        return ret;
}

static int process_all_extents(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_root *root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct extent_buffer *eb;
        int slot;

        root = sctx->send_root;
        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = sctx->cmp_key->objectid;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                eb = path->nodes[0];
                slot = path->slots[0];

                if (slot >= btrfs_header_nritems(eb)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0) {
                                goto out;
                        } else if (ret > 0) {
                                ret = 0;
                                break;
                        }
                        continue;
                }

                btrfs_item_key_to_cpu(eb, &found_key, slot);

                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        ret = 0;
                        goto out;
                }

                ret = process_extent(sctx, path, &found_key);
                if (ret < 0)
                        goto out;

                path->slots[0]++;
        }

out:
        btrfs_free_path(path);
        return ret;
}

static int process_recorded_refs_if_needed(struct send_ctx *sctx, int at_end,
                                           int *pending_move,
                                           int *refs_processed)
{
        int ret = 0;

        if (sctx->cur_ino == 0)
                goto out;
        if (!at_end && sctx->cur_ino == sctx->cmp_key->objectid &&
            sctx->cmp_key->type <= BTRFS_INODE_EXTREF_KEY)
                goto out;
        if (list_empty(&sctx->new_refs) && list_empty(&sctx->deleted_refs))
                goto out;

        ret = process_recorded_refs(sctx, pending_move);
        if (ret < 0)
                goto out;

        *refs_processed = 1;
out:
        return ret;
}

static int finish_inode_if_needed(struct send_ctx *sctx, int at_end)
{
        int ret = 0;
        u64 left_mode;
        u64 left_uid;
        u64 left_gid;
        u64 right_mode;
        u64 right_uid;
        u64 right_gid;
        int need_chmod = 0;
        int need_chown = 0;
        int pending_move = 0;
        int refs_processed = 0;

        ret = process_recorded_refs_if_needed(sctx, at_end, &pending_move,
                                              &refs_processed);
        if (ret < 0)
                goto out;

        /*
         * We have processed the refs and thus need to advance send_progress.
         * Now, calls to get_cur_xxx will take the updated refs of the current
         * inode into account.
         *
         * On the other hand, if our current inode is a directory and couldn't
         * be moved/renamed because its parent was renamed/moved too and it has
         * a higher inode number, we can only move/rename our current inode
         * after we moved/renamed its parent. Therefore in this case operate on
         * the old path (pre move/rename) of our current inode, and the
         * move/rename will be performed later.
         */
        if (refs_processed && !pending_move)
                sctx->send_progress = sctx->cur_ino + 1;

        if (sctx->cur_ino == 0 || sctx->cur_inode_deleted)
                goto out;
        if (!at_end && sctx->cmp_key->objectid == sctx->cur_ino)
                goto out;

        ret = get_inode_info(sctx->send_root, sctx->cur_ino, NULL, NULL,
                        &left_mode, &left_uid, &left_gid, NULL);
        if (ret < 0)
                goto out;

        if (!sctx->parent_root || sctx->cur_inode_new) {
                need_chown = 1;
                if (!S_ISLNK(sctx->cur_inode_mode))
                        need_chmod = 1;
        } else {
                ret = get_inode_info(sctx->parent_root, sctx->cur_ino,
                                NULL, NULL, &right_mode, &right_uid,
                                &right_gid, NULL);
                if (ret < 0)
                        goto out;

                if (left_uid != right_uid || left_gid != right_gid)
                        need_chown = 1;
                if (!S_ISLNK(sctx->cur_inode_mode) && left_mode != right_mode)
                        need_chmod = 1;
        }

        if (S_ISREG(sctx->cur_inode_mode)) {
                if (need_send_hole(sctx)) {
                        if (sctx->cur_inode_last_extent == (u64)-1 ||
                            sctx->cur_inode_last_extent <
                            sctx->cur_inode_size) {
                                ret = get_last_extent(sctx, (u64)-1);
                                if (ret)
                                        goto out;
                        }
                        if (sctx->cur_inode_last_extent <
                            sctx->cur_inode_size) {
                                ret = send_hole(sctx, sctx->cur_inode_size);
                                if (ret)
                                        goto out;
                        }
                }
                ret = send_truncate(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                sctx->cur_inode_size);
                if (ret < 0)
                        goto out;
        }

        if (need_chown) {
                ret = send_chown(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                left_uid, left_gid);
                if (ret < 0)
                        goto out;
        }
        if (need_chmod) {
                ret = send_chmod(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                left_mode);
                if (ret < 0)
                        goto out;
        }

        /*
         * If other directory inodes depended on our current directory
         * inode's move/rename, now do their move/rename operations.
         */
        if (!is_waiting_for_move(sctx, sctx->cur_ino)) {
                ret = apply_children_dir_moves(sctx);
                if (ret)
                        goto out;
                /*
                 * Need to send that every time, no matter if it actually
                 * changed between the two trees as we have done changes to
                 * the inode before. If our inode is a directory and it's
                 * waiting to be moved/renamed, we will send its utimes when
                 * it's moved/renamed, therefore we don't need to do it here.
                 */
                sctx->send_progress = sctx->cur_ino + 1;
                ret = send_utimes(sctx, sctx->cur_ino, sctx->cur_inode_gen);
                if (ret < 0)
                        goto out;
        }

out:
        return ret;
}

static int changed_inode(struct send_ctx *sctx,
                         enum btrfs_compare_tree_result result)
{
        int ret = 0;
        struct btrfs_key *key = sctx->cmp_key;
        struct btrfs_inode_item *left_ii = NULL;
        struct btrfs_inode_item *right_ii = NULL;
        u64 left_gen = 0;
        u64 right_gen = 0;

        sctx->cur_ino = key->objectid;
        sctx->cur_inode_new_gen = 0;
        sctx->cur_inode_last_extent = (u64)-1;

        /*
         * Set send_progress to current inode. This will tell all get_cur_xxx
         * functions that the current inode's refs are not updated yet. Later,
         * when process_recorded_refs is finished, it is set to cur_ino + 1.
         */
        sctx->send_progress = sctx->cur_ino;

        if (result == BTRFS_COMPARE_TREE_NEW ||
            result == BTRFS_COMPARE_TREE_CHANGED) {
                left_ii = btrfs_item_ptr(sctx->left_path->nodes[0],
                                sctx->left_path->slots[0],
                                struct btrfs_inode_item);
                left_gen = btrfs_inode_generation(sctx->left_path->nodes[0],
                                left_ii);
        } else {
                right_ii = btrfs_item_ptr(sctx->right_path->nodes[0],
                                sctx->right_path->slots[0],
                                struct btrfs_inode_item);
                right_gen = btrfs_inode_generation(sctx->right_path->nodes[0],
                                right_ii);
        }
        if (result == BTRFS_COMPARE_TREE_CHANGED) {
                right_ii = btrfs_item_ptr(sctx->right_path->nodes[0],
                                sctx->right_path->slots[0],
                                struct btrfs_inode_item);

                right_gen = btrfs_inode_generation(sctx->right_path->nodes[0],
                                right_ii);

                /*
                 * The cur_ino = root dir case is special here. We can't treat
                 * the inode as deleted+reused because it would generate a
                 * stream that tries to delete/mkdir the root dir.
                 */
                if (left_gen != right_gen &&
                    sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID)
                        sctx->cur_inode_new_gen = 1;
        }

        if (result == BTRFS_COMPARE_TREE_NEW) {
                sctx->cur_inode_gen = left_gen;
                sctx->cur_inode_new = 1;
                sctx->cur_inode_deleted = 0;
                sctx->cur_inode_size = btrfs_inode_size(
                                sctx->left_path->nodes[0], left_ii);
                sctx->cur_inode_mode = btrfs_inode_mode(
                                sctx->left_path->nodes[0], left_ii);
                sctx->cur_inode_rdev = btrfs_inode_rdev(
                                sctx->left_path->nodes[0], left_ii);
                if (sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID)
                        ret = send_create_inode_if_needed(sctx);
        } else if (result == BTRFS_COMPARE_TREE_DELETED) {
                sctx->cur_inode_gen = right_gen;
                sctx->cur_inode_new = 0;
                sctx->cur_inode_deleted = 1;
                sctx->cur_inode_size = btrfs_inode_size(
                                sctx->right_path->nodes[0], right_ii);
                sctx->cur_inode_mode = btrfs_inode_mode(
                                sctx->right_path->nodes[0], right_ii);
        } else if (result == BTRFS_COMPARE_TREE_CHANGED) {
                /*
                 * We need to do some special handling in case the inode was
                 * reported as changed with a changed generation number. This
                 * means that the original inode was deleted and new inode
                 * reused the same inum. So we have to treat the old inode as
                 * deleted and the new one as new.
                 */
                if (sctx->cur_inode_new_gen) {
                        /*
                         * First, process the inode as if it was deleted.
                         */
                        sctx->cur_inode_gen = right_gen;
                        sctx->cur_inode_new = 0;
                        sctx->cur_inode_deleted = 1;
                        sctx->cur_inode_size = btrfs_inode_size(
                                        sctx->right_path->nodes[0], right_ii);
                        sctx->cur_inode_mode = btrfs_inode_mode(
                                        sctx->right_path->nodes[0], right_ii);
                        ret = process_all_refs(sctx,
                                        BTRFS_COMPARE_TREE_DELETED);
                        if (ret < 0)
                                goto out;

                        /*
                         * Now process the inode as if it was new.
                         */
                        sctx->cur_inode_gen = left_gen;
                        sctx->cur_inode_new = 1;
                        sctx->cur_inode_deleted = 0;
                        sctx->cur_inode_size = btrfs_inode_size(
                                        sctx->left_path->nodes[0], left_ii);
                        sctx->cur_inode_mode = btrfs_inode_mode(
                                        sctx->left_path->nodes[0], left_ii);
                        sctx->cur_inode_rdev = btrfs_inode_rdev(
                                        sctx->left_path->nodes[0], left_ii);
                        ret = send_create_inode_if_needed(sctx);
                        if (ret < 0)
                                goto out;

                        ret = process_all_refs(sctx, BTRFS_COMPARE_TREE_NEW);
                        if (ret < 0)
                                goto out;
                        /*
                         * Advance send_progress now as we did not get into
                         * process_recorded_refs_if_needed in the new_gen case.
                         */
                        sctx->send_progress = sctx->cur_ino + 1;

                        /*
                         * Now process all extents and xattrs of the inode as if
                         * they were all new.
                         */
                        ret = process_all_extents(sctx);
                        if (ret < 0)
                                goto out;
                        ret = process_all_new_xattrs(sctx);
                        if (ret < 0)
                                goto out;
                } else {
                        sctx->cur_inode_gen = left_gen;
                        sctx->cur_inode_new = 0;
                        sctx->cur_inode_new_gen = 0;
                        sctx->cur_inode_deleted = 0;
                        sctx->cur_inode_size = btrfs_inode_size(
                                        sctx->left_path->nodes[0], left_ii);
                        sctx->cur_inode_mode = btrfs_inode_mode(
                                        sctx->left_path->nodes[0], left_ii);
                }
        }

out:
        return ret;
}

/*
 * We have to process new refs before deleted refs, but compare_trees gives us
 * the new and deleted refs mixed. To fix this, we record the new/deleted refs
 * first and later process them in process_recorded_refs.
 * For the cur_inode_new_gen case, we skip recording completely because
 * changed_inode did already initiate processing of refs. The reason for this is
 * that in this case, compare_tree actually compares the refs of 2 different
 * inodes. To fix this, process_all_refs is used in changed_inode to handle all
 * refs of the right tree as deleted and all refs of the left tree as new.
 */
static int changed_ref(struct send_ctx *sctx,
                       enum btrfs_compare_tree_result result)
{
        int ret = 0;

        if (sctx->cur_ino != sctx->cmp_key->objectid) {
                inconsistent_snapshot_error(sctx, result, "reference");
                return -EIO;
        }

        if (!sctx->cur_inode_new_gen &&
            sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID) {
                if (result == BTRFS_COMPARE_TREE_NEW)
                        ret = record_new_ref(sctx);
                else if (result == BTRFS_COMPARE_TREE_DELETED)
                        ret = record_deleted_ref(sctx);
                else if (result == BTRFS_COMPARE_TREE_CHANGED)
                        ret = record_changed_ref(sctx);
        }

        return ret;
}

/*
 * Process new/deleted/changed xattrs. We skip processing in the
 * cur_inode_new_gen case because changed_inode did already initiate processing
 * of xattrs. The reason is the same as in changed_ref
 */
static int changed_xattr(struct send_ctx *sctx,
                         enum btrfs_compare_tree_result result)
{
        int ret = 0;

        if (sctx->cur_ino != sctx->cmp_key->objectid) {
                inconsistent_snapshot_error(sctx, result, "xattr");
                return -EIO;
        }

        if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
                if (result == BTRFS_COMPARE_TREE_NEW)
                        ret = process_new_xattr(sctx);
                else if (result == BTRFS_COMPARE_TREE_DELETED)
                        ret = process_deleted_xattr(sctx);
                else if (result == BTRFS_COMPARE_TREE_CHANGED)
                        ret = process_changed_xattr(sctx);
        }

        return ret;
}

/*
 * Process new/deleted/changed extents. We skip processing in the
 * cur_inode_new_gen case because changed_inode did already initiate processing
 * of extents. The reason is the same as in changed_ref
 */
static int changed_extent(struct send_ctx *sctx,
                          enum btrfs_compare_tree_result result)
{
        int ret = 0;

        if (sctx->cur_ino != sctx->cmp_key->objectid) {

                if (result == BTRFS_COMPARE_TREE_CHANGED) {
                        struct extent_buffer *leaf_l;
                        struct extent_buffer *leaf_r;
                        struct btrfs_file_extent_item *ei_l;
                        struct btrfs_file_extent_item *ei_r;

                        leaf_l = sctx->left_path->nodes[0];
                        leaf_r = sctx->right_path->nodes[0];
                        ei_l = btrfs_item_ptr(leaf_l,
                                              sctx->left_path->slots[0],
                                              struct btrfs_file_extent_item);
                        ei_r = btrfs_item_ptr(leaf_r,
                                              sctx->right_path->slots[0],
                                              struct btrfs_file_extent_item);

                        /*
                         * We may have found an extent item that has changed
                         * only its disk_bytenr field and the corresponding
                         * inode item was not updated. This case happens due to
                         * very specific timings during relocation when a leaf
                         * that contains file extent items is COWed while
                         * relocation is ongoing and its in the stage where it
                         * updates data pointers. So when this happens we can
                         * safely ignore it since we know it's the same extent,
                         * but just at different logical and physical locations
                         * (when an extent is fully replaced with a new one, we
                         * know the generation number must have changed too,
                         * since snapshot creation implies committing the current
                         * transaction, and the inode item must have been updated
                         * as well).
                         * This replacement of the disk_bytenr happens at
                         * relocation.c:replace_file_extents() through
                         * relocation.c:btrfs_reloc_cow_block().
                         */
                        if (btrfs_file_extent_generation(leaf_l, ei_l) ==
                            btrfs_file_extent_generation(leaf_r, ei_r) &&
                            btrfs_file_extent_ram_bytes(leaf_l, ei_l) ==
                            btrfs_file_extent_ram_bytes(leaf_r, ei_r) &&
                            btrfs_file_extent_compression(leaf_l, ei_l) ==
                            btrfs_file_extent_compression(leaf_r, ei_r) &&
                            btrfs_file_extent_encryption(leaf_l, ei_l) ==
                            btrfs_file_extent_encryption(leaf_r, ei_r) &&
                            btrfs_file_extent_other_encoding(leaf_l, ei_l) ==
                            btrfs_file_extent_other_encoding(leaf_r, ei_r) &&
                            btrfs_file_extent_type(leaf_l, ei_l) ==
                            btrfs_file_extent_type(leaf_r, ei_r) &&
                            btrfs_file_extent_disk_bytenr(leaf_l, ei_l) !=
                            btrfs_file_extent_disk_bytenr(leaf_r, ei_r) &&
                            btrfs_file_extent_disk_num_bytes(leaf_l, ei_l) ==
                            btrfs_file_extent_disk_num_bytes(leaf_r, ei_r) &&
                            btrfs_file_extent_offset(leaf_l, ei_l) ==
                            btrfs_file_extent_offset(leaf_r, ei_r) &&
                            btrfs_file_extent_num_bytes(leaf_l, ei_l) ==
                            btrfs_file_extent_num_bytes(leaf_r, ei_r))
                                return 0;
                }

                inconsistent_snapshot_error(sctx, result, "extent");
                return -EIO;
        }

        if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
                if (result != BTRFS_COMPARE_TREE_DELETED)
                        ret = process_extent(sctx, sctx->left_path,
                                        sctx->cmp_key);
        }

        return ret;
}

static int dir_changed(struct send_ctx *sctx, u64 dir)
{
        u64 orig_gen, new_gen;
        int ret;

        ret = get_inode_info(sctx->send_root, dir, NULL, &new_gen, NULL, NULL,
                             NULL, NULL);
        if (ret)
                return ret;

        ret = get_inode_info(sctx->parent_root, dir, NULL, &orig_gen, NULL,
                             NULL, NULL, NULL);
        if (ret)
                return ret;

        return (orig_gen != new_gen) ? 1 : 0;
}

static int compare_refs(struct send_ctx *sctx, struct btrfs_path *path,
                        struct btrfs_key *key)
{
        struct btrfs_inode_extref *extref;
        struct extent_buffer *leaf;
        u64 dirid = 0, last_dirid = 0;
        unsigned long ptr;
        u32 item_size;
        u32 cur_offset = 0;
        int ref_name_len;
        int ret = 0;

        /* Easy case, just check this one dirid */
        if (key->type == BTRFS_INODE_REF_KEY) {
                dirid = key->offset;

                ret = dir_changed(sctx, dirid);
                goto out;
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
        while (cur_offset < item_size) {
                extref = (struct btrfs_inode_extref *)(ptr +
                                                       cur_offset);
                dirid = btrfs_inode_extref_parent(leaf, extref);
                ref_name_len = btrfs_inode_extref_name_len(leaf, extref);
                cur_offset += ref_name_len + sizeof(*extref);
                if (dirid == last_dirid)
                        continue;
                ret = dir_changed(sctx, dirid);
                if (ret)
                        break;
                last_dirid = dirid;
        }
out:
        return ret;
}

/*
 * Updates compare related fields in sctx and simply forwards to the actual
 * changed_xxx functions.
 */
static int changed_cb(struct btrfs_root *left_root,
                      struct btrfs_root *right_root,
                      struct btrfs_path *left_path,
                      struct btrfs_path *right_path,
                      struct btrfs_key *key,
                      enum btrfs_compare_tree_result result,
                      void *ctx)
{
        int ret = 0;
        struct send_ctx *sctx = ctx;

        if (result == BTRFS_COMPARE_TREE_SAME) {
                if (key->type == BTRFS_INODE_REF_KEY ||
                    key->type == BTRFS_INODE_EXTREF_KEY) {
                        ret = compare_refs(sctx, left_path, key);
                        if (!ret)
                                return 0;
                        if (ret < 0)
                                return ret;
                } else if (key->type == BTRFS_EXTENT_DATA_KEY) {
                        return maybe_send_hole(sctx, left_path, key);
                } else {
                        return 0;
                }
                result = BTRFS_COMPARE_TREE_CHANGED;
                ret = 0;
        }

        sctx->left_path = left_path;
        sctx->right_path = right_path;
        sctx->cmp_key = key;

        ret = finish_inode_if_needed(sctx, 0);
        if (ret < 0)
                goto out;

        /* Ignore non-FS objects */
        if (key->objectid == BTRFS_FREE_INO_OBJECTID ||
            key->objectid == BTRFS_FREE_SPACE_OBJECTID)
                goto out;

        if (key->type == BTRFS_INODE_ITEM_KEY)
                ret = changed_inode(sctx, result);
        else if (key->type == BTRFS_INODE_REF_KEY ||
                 key->type == BTRFS_INODE_EXTREF_KEY)
                ret = changed_ref(sctx, result);
        else if (key->type == BTRFS_XATTR_ITEM_KEY)
                ret = changed_xattr(sctx, result);
        else if (key->type == BTRFS_EXTENT_DATA_KEY)
                ret = changed_extent(sctx, result);

out:
        return ret;
}

static int full_send_tree(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_root *send_root = sctx->send_root;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_path *path;
        struct extent_buffer *eb;
        int slot;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = BTRFS_FIRST_FREE_OBJECTID;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(send_root, &key, path, 1, 0);
        if (ret < 0)
                goto out;
        if (ret)
                goto out_finish;

        while (1) {
                eb = path->nodes[0];
                slot = path->slots[0];
                btrfs_item_key_to_cpu(eb, &found_key, slot);

                ret = changed_cb(send_root, NULL, path, NULL,
                                &found_key, BTRFS_COMPARE_TREE_NEW, sctx);
                if (ret < 0)
                        goto out;

                key.objectid = found_key.objectid;
                key.type = found_key.type;
                key.offset = found_key.offset + 1;

                ret = btrfs_next_item(send_root, path);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret  = 0;
                        break;
                }
        }

out_finish:
        ret = finish_inode_if_needed(sctx, 1);

out:
        btrfs_free_path(path);
        return ret;
}

static int send_subvol(struct send_ctx *sctx)
{
        int ret;

        if (!(sctx->flags & BTRFS_SEND_FLAG_OMIT_STREAM_HEADER)) {
                ret = send_header(sctx);
                if (ret < 0)
                        goto out;
        }

        ret = send_subvol_begin(sctx);
        if (ret < 0)
                goto out;

        if (sctx->parent_root) {
                ret = btrfs_compare_trees(sctx->send_root, sctx->parent_root,
                                changed_cb, sctx);
                if (ret < 0)
                        goto out;
                ret = finish_inode_if_needed(sctx, 1);
                if (ret < 0)
                        goto out;
        } else {
                ret = full_send_tree(sctx);
                if (ret < 0)
                        goto out;
        }

out:
        free_recorded_refs(sctx);
        return ret;
}

/*
 * If orphan cleanup did remove any orphans from a root, it means the tree
 * was modified and therefore the commit root is not the same as the current
 * root anymore. This is a problem, because send uses the commit root and
 * therefore can see inode items that don't exist in the current root anymore,
 * and for example make calls to btrfs_iget, which will do tree lookups based
 * on the current root and not on the commit root. Those lookups will fail,
 * returning a -ESTALE error, and making send fail with that error. So make
 * sure a send does not see any orphans we have just removed, and that it will
 * see the same inodes regardless of whether a transaction commit happened
 * before it started (meaning that the commit root will be the same as the
 * current root) or not.
 */
static int ensure_commit_roots_uptodate(struct send_ctx *sctx)
{
        int i;
        struct btrfs_trans_handle *trans = NULL;

again:
        if (sctx->parent_root &&
            sctx->parent_root->node != sctx->parent_root->commit_root)
                goto commit_trans;

        for (i = 0; i < sctx->clone_roots_cnt; i++)
                if (sctx->clone_roots[i].root->node !=
                    sctx->clone_roots[i].root->commit_root)
                        goto commit_trans;

        if (trans)
                return btrfs_end_transaction(trans);

        return 0;

commit_trans:
        /* Use any root, all fs roots will get their commit roots updated. */
        if (!trans) {
                trans = btrfs_join_transaction(sctx->send_root);
                if (IS_ERR(trans))
                        return PTR_ERR(trans);
                goto again;
        }

        return btrfs_commit_transaction(trans);
}

static void btrfs_root_dec_send_in_progress(struct btrfs_root* root)
{
        spin_lock(&root->root_item_lock);
        root->send_in_progress--;
        /*
         * Not much left to do, we don't know why it's unbalanced and
         * can't blindly reset it to 0.
         */
        if (root->send_in_progress < 0)
                btrfs_err(root->fs_info,
                          "send_in_progres unbalanced %d root %llu",
                          root->send_in_progress, root->root_key.objectid);
        spin_unlock(&root->root_item_lock);
}

long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
{
        int ret = 0;
        struct btrfs_root *send_root = BTRFS_I(file_inode(mnt_file))->root;
        struct btrfs_fs_info *fs_info = send_root->fs_info;
        struct btrfs_root *clone_root;
        struct btrfs_ioctl_send_args *arg = NULL;
        struct btrfs_key key;
        struct send_ctx *sctx = NULL;
        u32 i;
        u64 *clone_sources_tmp = NULL;
        int clone_sources_to_rollback = 0;
        unsigned alloc_size;
        int sort_clone_roots = 0;
        int index;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        /*
         * The subvolume must remain read-only during send, protect against
         * making it RW. This also protects against deletion.
         */
        spin_lock(&send_root->root_item_lock);
        send_root->send_in_progress++;
        spin_unlock(&send_root->root_item_lock);

        /*
         * This is done when we lookup the root, it should already be complete
         * by the time we get here.
         */
        WARN_ON(send_root->orphan_cleanup_state != ORPHAN_CLEANUP_DONE);

        /*
         * Userspace tools do the checks and warn the user if it's
         * not RO.
         */
        if (!btrfs_root_readonly(send_root)) {
                ret = -EPERM;
                goto out;
        }

        arg = memdup_user(arg_, sizeof(*arg));
        if (IS_ERR(arg)) {
                ret = PTR_ERR(arg);
                arg = NULL;
                goto out;
        }

        if (arg->clone_sources_count >
            ULLONG_MAX / sizeof(*arg->clone_sources)) {
                ret = -EINVAL;
                goto out;
        }

        if (!access_ok(VERIFY_READ, arg->clone_sources,
                        sizeof(*arg->clone_sources) *
                        arg->clone_sources_count)) {
                ret = -EFAULT;
                goto out;
        }

        if (arg->flags & ~BTRFS_SEND_FLAG_MASK) {
                ret = -EINVAL;
                goto out;
        }

        sctx = kzalloc(sizeof(struct send_ctx), GFP_KERNEL);
        if (!sctx) {
                ret = -ENOMEM;
                goto out;
        }

        INIT_LIST_HEAD(&sctx->new_refs);
        INIT_LIST_HEAD(&sctx->deleted_refs);
        INIT_RADIX_TREE(&sctx->name_cache, GFP_KERNEL);
        INIT_LIST_HEAD(&sctx->name_cache_list);

        sctx->flags = arg->flags;

        sctx->send_filp = fget(arg->send_fd);
        if (!sctx->send_filp) {
                ret = -EBADF;
                goto out;
        }

        sctx->send_root = send_root;
        /*
         * Unlikely but possible, if the subvolume is marked for deletion but
         * is slow to remove the directory entry, send can still be started
         */
        if (btrfs_root_dead(sctx->send_root)) {
                ret = -EPERM;
                goto out;
        }

        sctx->clone_roots_cnt = arg->clone_sources_count;

        sctx->send_max_size = BTRFS_SEND_BUF_SIZE;
        sctx->send_buf = kmalloc(sctx->send_max_size, GFP_KERNEL | __GFP_NOWARN);
        if (!sctx->send_buf) {
                sctx->send_buf = vmalloc(sctx->send_max_size);
                if (!sctx->send_buf) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        sctx->read_buf = kmalloc(BTRFS_SEND_READ_SIZE, GFP_KERNEL | __GFP_NOWARN);
        if (!sctx->read_buf) {
                sctx->read_buf = vmalloc(BTRFS_SEND_READ_SIZE);
                if (!sctx->read_buf) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        sctx->pending_dir_moves = RB_ROOT;
        sctx->waiting_dir_moves = RB_ROOT;
        sctx->orphan_dirs = RB_ROOT;

        alloc_size = sizeof(struct clone_root) * (arg->clone_sources_count + 1);

        sctx->clone_roots = kzalloc(alloc_size, GFP_KERNEL | __GFP_NOWARN);
        if (!sctx->clone_roots) {
                sctx->clone_roots = vzalloc(alloc_size);
                if (!sctx->clone_roots) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        alloc_size = arg->clone_sources_count * sizeof(*arg->clone_sources);

        if (arg->clone_sources_count) {
                clone_sources_tmp = kmalloc(alloc_size, GFP_KERNEL | __GFP_NOWARN);
                if (!clone_sources_tmp) {
                        clone_sources_tmp = vmalloc(alloc_size);
                        if (!clone_sources_tmp) {
                                ret = -ENOMEM;
                                goto out;
                        }
                }

                ret = copy_from_user(clone_sources_tmp, arg->clone_sources,
                                alloc_size);
                if (ret) {
                        ret = -EFAULT;
                        goto out;
                }

                for (i = 0; i < arg->clone_sources_count; i++) {
                        key.objectid = clone_sources_tmp[i];
                        key.type = BTRFS_ROOT_ITEM_KEY;
                        key.offset = (u64)-1;

                        index = srcu_read_lock(&fs_info->subvol_srcu);

                        clone_root = btrfs_read_fs_root_no_name(fs_info, &key);
                        if (IS_ERR(clone_root)) {
                                srcu_read_unlock(&fs_info->subvol_srcu, index);
                                ret = PTR_ERR(clone_root);
                                goto out;
                        }
                        spin_lock(&clone_root->root_item_lock);
                        if (!btrfs_root_readonly(clone_root) ||
                            btrfs_root_dead(clone_root)) {
                                spin_unlock(&clone_root->root_item_lock);
                                srcu_read_unlock(&fs_info->subvol_srcu, index);
                                ret = -EPERM;
                                goto out;
                        }
                        clone_root->send_in_progress++;
                        spin_unlock(&clone_root->root_item_lock);
                        srcu_read_unlock(&fs_info->subvol_srcu, index);

                        sctx->clone_roots[i].root = clone_root;
                        clone_sources_to_rollback = i + 1;
                }
                kvfree(clone_sources_tmp);
                clone_sources_tmp = NULL;
        }

        if (arg->parent_root) {
                key.objectid = arg->parent_root;
                key.type = BTRFS_ROOT_ITEM_KEY;
                key.offset = (u64)-1;

                index = srcu_read_lock(&fs_info->subvol_srcu);

                sctx->parent_root = btrfs_read_fs_root_no_name(fs_info, &key);
                if (IS_ERR(sctx->parent_root)) {
                        srcu_read_unlock(&fs_info->subvol_srcu, index);
                        ret = PTR_ERR(sctx->parent_root);
                        goto out;
                }

                spin_lock(&sctx->parent_root->root_item_lock);
                sctx->parent_root->send_in_progress++;
                if (!btrfs_root_readonly(sctx->parent_root) ||
                                btrfs_root_dead(sctx->parent_root)) {
                        spin_unlock(&sctx->parent_root->root_item_lock);
                        srcu_read_unlock(&fs_info->subvol_srcu, index);
                        ret = -EPERM;
                        goto out;
                }
                spin_unlock(&sctx->parent_root->root_item_lock);

                srcu_read_unlock(&fs_info->subvol_srcu, index);
        }

        /*
         * Clones from send_root are allowed, but only if the clone source
         * is behind the current send position. This is checked while searching
         * for possible clone sources.
         */
        sctx->clone_roots[sctx->clone_roots_cnt++].root = sctx->send_root;

        /* We do a bsearch later */
        sort(sctx->clone_roots, sctx->clone_roots_cnt,
                        sizeof(*sctx->clone_roots), __clone_root_cmp_sort,
                        NULL);
        sort_clone_roots = 1;

        ret = ensure_commit_roots_uptodate(sctx);
        if (ret)
                goto out;

        current->journal_info = BTRFS_SEND_TRANS_STUB;
        ret = send_subvol(sctx);
        current->journal_info = NULL;
        if (ret < 0)
                goto out;

        if (!(sctx->flags & BTRFS_SEND_FLAG_OMIT_END_CMD)) {
                ret = begin_cmd(sctx, BTRFS_SEND_C_END);
                if (ret < 0)
                        goto out;
                ret = send_cmd(sctx);
                if (ret < 0)
                        goto out;
        }

out:
        WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->pending_dir_moves));
        while (sctx && !RB_EMPTY_ROOT(&sctx->pending_dir_moves)) {
                struct rb_node *n;
                struct pending_dir_move *pm;

                n = rb_first(&sctx->pending_dir_moves);
                pm = rb_entry(n, struct pending_dir_move, node);
                while (!list_empty(&pm->list)) {
                        struct pending_dir_move *pm2;

                        pm2 = list_first_entry(&pm->list,
                                               struct pending_dir_move, list);
                        free_pending_move(sctx, pm2);
                }
                free_pending_move(sctx, pm);
        }

        WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->waiting_dir_moves));
        while (sctx && !RB_EMPTY_ROOT(&sctx->waiting_dir_moves)) {
                struct rb_node *n;
                struct waiting_dir_move *dm;

                n = rb_first(&sctx->waiting_dir_moves);
                dm = rb_entry(n, struct waiting_dir_move, node);
                rb_erase(&dm->node, &sctx->waiting_dir_moves);
                kfree(dm);
        }

        WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->orphan_dirs));
        while (sctx && !RB_EMPTY_ROOT(&sctx->orphan_dirs)) {
                struct rb_node *n;
                struct orphan_dir_info *odi;

                n = rb_first(&sctx->orphan_dirs);
                odi = rb_entry(n, struct orphan_dir_info, node);
                free_orphan_dir_info(sctx, odi);
        }

        if (sort_clone_roots) {
                for (i = 0; i < sctx->clone_roots_cnt; i++)
                        btrfs_root_dec_send_in_progress(
                                        sctx->clone_roots[i].root);
        } else {
                for (i = 0; sctx && i < clone_sources_to_rollback; i++)
                        btrfs_root_dec_send_in_progress(
                                        sctx->clone_roots[i].root);

                btrfs_root_dec_send_in_progress(send_root);
        }
        if (sctx && !IS_ERR_OR_NULL(sctx->parent_root))
                btrfs_root_dec_send_in_progress(sctx->parent_root);

        kfree(arg);
        kvfree(clone_sources_tmp);

        if (sctx) {
                if (sctx->send_filp)
                        fput(sctx->send_filp);

                kvfree(sctx->clone_roots);
                kvfree(sctx->send_buf);
                kvfree(sctx->read_buf);

                name_cache_free(sctx);

                kfree(sctx);
        }

        return ret;
}