[linux.git] / fs / kernfs / mount.c

/*
 * fs/kernfs/mount.c - kernfs mount implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007, 2013 Tejun Heo <[email protected]>
 *
 * This file is released under the GPLv2.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/seq_file.h>
#include <linux/exportfs.h>

#include "kernfs-internal.h"

struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;

static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
{
	struct kernfs_root *root = kernfs_info(sb)->root;
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->remount_fs)
		return scops->remount_fs(root, flags, data);
	return 0;
}

static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
{
	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->show_options)
		return scops->show_options(sf, root);
	return 0;
}

static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
{
	struct kernfs_node *node = kernfs_dentry_node(dentry);
	struct kernfs_root *root = kernfs_root(node);
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->show_path)
		return scops->show_path(sf, node, root);

	seq_dentry(sf, dentry, " \t\n\\");
	return 0;
}

const struct super_operations kernfs_sops = {
	.statfs		= simple_statfs,
	.drop_inode	= generic_delete_inode,
	.evict_inode	= kernfs_evict_inode,

	.remount_fs	= kernfs_sop_remount_fs,
	.show_options	= kernfs_sop_show_options,
	.show_path	= kernfs_sop_show_path,
};

/*
 * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
 * number and generation
 */
struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
	const union kernfs_node_id *id)
{
	struct kernfs_node *kn;

	kn = kernfs_find_and_get_node_by_ino(root, id->ino);
	if (!kn)
		return NULL;
	if (kn->id.generation != id->generation) {
		kernfs_put(kn);
		return NULL;
	}
	return kn;
}

static struct inode *kernfs_fh_get_inode(struct super_block *sb,
		u64 ino, u32 generation)
{
	struct kernfs_super_info *info = kernfs_info(sb);
	struct inode *inode;
	struct kernfs_node *kn;

	if (ino == 0)
		return ERR_PTR(-ESTALE);

	kn = kernfs_find_and_get_node_by_ino(info->root, ino);
	if (!kn)
		return ERR_PTR(-ESTALE);
	inode = kernfs_get_inode(sb, kn);
	kernfs_put(kn);
	if (!inode)
		return ERR_PTR(-ESTALE);

	if (generation && inode->i_generation != generation) {
		/* we didn't find the right inode.. */
		iput(inode);
		return ERR_PTR(-ESTALE);
	}
	return inode;
}

static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
		int fh_len, int fh_type)
{
	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
				    kernfs_fh_get_inode);
}

static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
		int fh_len, int fh_type)
{
	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
				    kernfs_fh_get_inode);
}

static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
{
	struct kernfs_node *kn = kernfs_dentry_node(child);

	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
}

static const struct export_operations kernfs_export_ops = {
	.fh_to_dentry	= kernfs_fh_to_dentry,
	.fh_to_parent	= kernfs_fh_to_parent,
	.get_parent	= kernfs_get_parent_dentry,
};

/**
 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
 * @sb: the super_block in question
 *
 * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
 * %NULL is returned.
 */
struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
{
	if (sb->s_op == &kernfs_sops)
		return kernfs_info(sb)->root;
	return NULL;
}

/*
 * find the next ancestor in the path down to @child, where @parent was the
 * ancestor whose descendant we want to find.
 *
 * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
 * node.  If @parent is b, then we return the node for c.
 * Passing in d as @parent is not ok.
 */
static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
					      struct kernfs_node *parent)
{
	if (child == parent) {
		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
		return NULL;
	}

	while (child->parent != parent) {
		if (!child->parent)
			return NULL;
		child = child->parent;
	}

	return child;
}

/**
 * kernfs_node_dentry - get a dentry for the given kernfs_node
 * @kn: kernfs_node for which a dentry is needed
 * @sb: the kernfs super_block
 */
struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
				  struct super_block *sb)
{
	struct dentry *dentry;
	struct kernfs_node *knparent = NULL;

	BUG_ON(sb->s_op != &kernfs_sops);

	dentry = dget(sb->s_root);

	/* Check if this is the root kernfs_node */
	if (!kn->parent)
		return dentry;

	knparent = find_next_ancestor(kn, NULL);
	if (WARN_ON(!knparent)) {
		dput(dentry);
		return ERR_PTR(-EINVAL);
	}

	do {
		struct dentry *dtmp;
		struct kernfs_node *kntmp;

		if (kn == knparent)
			return dentry;
		kntmp = find_next_ancestor(kn, knparent);
		if (WARN_ON(!kntmp)) {
			dput(dentry);
			return ERR_PTR(-EINVAL);
		}
		dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
					       strlen(kntmp->name));
		dput(dentry);
		if (IS_ERR(dtmp))
			return dtmp;
		knparent = kntmp;
		dentry = dtmp;
	} while (true);
}

static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
{
	struct kernfs_super_info *info = kernfs_info(sb);
	struct inode *inode;
	struct dentry *root;

	info->sb = sb;
	/* Userspace would break if executables or devices appear on sysfs */
	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
	sb->s_blocksize = PAGE_SIZE;
	sb->s_blocksize_bits = PAGE_SHIFT;
	sb->s_magic = magic;
	sb->s_op = &kernfs_sops;
	sb->s_xattr = kernfs_xattr_handlers;
	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
		sb->s_export_op = &kernfs_export_ops;
	sb->s_time_gran = 1;

	/* sysfs dentries and inodes don't require IO to create */
	sb->s_shrink.seeks = 0;

	/* get root inode, initialize and unlock it */
	mutex_lock(&kernfs_mutex);
	inode = kernfs_get_inode(sb, info->root->kn);
	mutex_unlock(&kernfs_mutex);
	if (!inode) {
		pr_debug("kernfs: could not get root inode\n");
		return -ENOMEM;
	}

	/* instantiate and link root dentry */
	root = d_make_root(inode);
	if (!root) {
		pr_debug("%s: could not get root dentry!\n", __func__);
		return -ENOMEM;
	}
	sb->s_root = root;
	sb->s_d_op = &kernfs_dops;
	return 0;
}

static int kernfs_test_super(struct super_block *sb, void *data)
{
	struct kernfs_super_info *sb_info = kernfs_info(sb);
	struct kernfs_super_info *info = data;

	return sb_info->root == info->root && sb_info->ns == info->ns;
}

static int kernfs_set_super(struct super_block *sb, void *data)
{
	int error;
	error = set_anon_super(sb, data);
	if (!error)
		sb->s_fs_info = data;
	return error;
}

/**
 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 * @sb: super_block of interest
 *
 * Return the namespace tag associated with kernfs super_block @sb.
 */
const void *kernfs_super_ns(struct super_block *sb)
{
	struct kernfs_super_info *info = kernfs_info(sb);

	return info->ns;
}

/**
 * kernfs_mount_ns - kernfs mount helper
 * @fs_type: file_system_type of the fs being mounted
 * @flags: mount flags specified for the mount
 * @root: kernfs_root of the hierarchy being mounted
 * @magic: file system specific magic number
 * @new_sb_created: tell the caller if we allocated a new superblock
 * @ns: optional namespace tag of the mount
 *
 * This is to be called from each kernfs user's file_system_type->mount()
 * implementation, which should pass through the specified @fs_type and
 * @flags, and specify the hierarchy and namespace tag to mount via @root
 * and @ns, respectively.
 *
 * The return value can be passed to the vfs layer verbatim.
 */
struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
				struct kernfs_root *root, unsigned long magic,
				bool *new_sb_created, const void *ns)
{
	struct super_block *sb;
	struct kernfs_super_info *info;
	int error;

	info = kzalloc(sizeof(*info), GFP_KERNEL);
	if (!info)
		return ERR_PTR(-ENOMEM);

	info->root = root;
	info->ns = ns;
	INIT_LIST_HEAD(&info->node);

	sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
			 &init_user_ns, info);
	if (IS_ERR(sb) || sb->s_fs_info != info)
		kfree(info);
	if (IS_ERR(sb))
		return ERR_CAST(sb);

	if (new_sb_created)
		*new_sb_created = !sb->s_root;

	if (!sb->s_root) {
		struct kernfs_super_info *info = kernfs_info(sb);

		error = kernfs_fill_super(sb, magic);
		if (error) {
			deactivate_locked_super(sb);
			return ERR_PTR(error);
		}
		sb->s_flags |= SB_ACTIVE;

		mutex_lock(&kernfs_mutex);
		list_add(&info->node, &root->supers);
		mutex_unlock(&kernfs_mutex);
	}

	return dget(sb->s_root);
}

/**
 * kernfs_kill_sb - kill_sb for kernfs
 * @sb: super_block being killed
 *
 * This can be used directly for file_system_type->kill_sb().  If a kernfs
 * user needs extra cleanup, it can implement its own kill_sb() and call
 * this function at the end.
 */
void kernfs_kill_sb(struct super_block *sb)
{
	struct kernfs_super_info *info = kernfs_info(sb);

	mutex_lock(&kernfs_mutex);
	list_del(&info->node);
	mutex_unlock(&kernfs_mutex);

	/*
	 * Remove the superblock from fs_supers/s_instances
	 * so we can't find it, before freeing kernfs_super_info.
	 */
	kill_anon_super(sb);
	kfree(info);
}

/**
 * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
 * @kernfs_root: the kernfs_root in question
 * @ns: the namespace tag
 *
 * Pin the superblock so the superblock won't be destroyed in subsequent
 * operations.  This can be used to block ->kill_sb() which may be useful
 * for kernfs users which dynamically manage superblocks.
 *
 * Returns NULL if there's no superblock associated to this kernfs_root, or
 * -EINVAL if the superblock is being freed.
 */
struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
{
	struct kernfs_super_info *info;
	struct super_block *sb = NULL;

	mutex_lock(&kernfs_mutex);
	list_for_each_entry(info, &root->supers, node) {
		if (info->ns == ns) {
			sb = info->sb;
			if (!atomic_inc_not_zero(&info->sb->s_active))
				sb = ERR_PTR(-EINVAL);
			break;
		}
	}
	mutex_unlock(&kernfs_mutex);
	return sb;
}

void __init kernfs_init(void)
{

	/*
	 * the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
	 * can access the slab lock free. This could introduce stale nodes,
	 * please see how kernfs_find_and_get_node_by_ino filters out stale
	 * nodes.
	 */
	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
					      sizeof(struct kernfs_node),
					      0,
					      SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
					      NULL);

	/* Creates slab cache for kernfs inode attributes */
	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
					      sizeof(struct kernfs_iattrs),
					      0, SLAB_PANIC, NULL);
}
Commit	Line	Data
b8441ed2 TH	1	/*
	2	* fs/kernfs/mount.c - kernfs mount implementation
	3	*
	4	* Copyright (c) 2001-3 Patrick Mochel
	5	* Copyright (c) 2007 SUSE Linux Products GmbH
	6	* Copyright (c) 2007, 2013 Tejun Heo <[email protected]>
	7	*
	8	* This file is released under the GPLv2.
	9	*/
fa736a95 TH	10
	11	#include <linux/fs.h>
	12	#include <linux/mount.h>
	13	#include <linux/init.h>
	14	#include <linux/magic.h>
	15	#include <linux/slab.h>
	16	#include <linux/pagemap.h>
fb3c8315	17	#include <linux/namei.h>
4f41fc59	18	#include <linux/seq_file.h>
aa818825	19	#include <linux/exportfs.h>
fa736a95 TH	20
	21	#include "kernfs-internal.h"
	22
26e28d68	23	struct kmem_cache kernfs_node_cache, kernfs_iattrs_cache;
fa736a95	24
6a7fed4e TH	25	static int kernfs_sop_remount_fs(struct super_block sb, int flags, char *data)
	26	{
	27	struct kernfs_root *root = kernfs_info(sb)->root;
	28	struct kernfs_syscall_ops *scops = root->syscall_ops;
	29
	30	if (scops && scops->remount_fs)
	31	return scops->remount_fs(root, flags, data);
	32	return 0;
	33	}
	34
	35	static int kernfs_sop_show_options(struct seq_file sf, struct dentry dentry)
	36	{
319ba91d	37	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
6a7fed4e TH	38	struct kernfs_syscall_ops *scops = root->syscall_ops;
	39
	40	if (scops && scops->show_options)
	41	return scops->show_options(sf, root);
	42	return 0;
	43	}
	44
4f41fc59 SH	45	static int kernfs_sop_show_path(struct seq_file sf, struct dentry dentry)
4f41fc59 SH	46	{
319ba91d	47	struct kernfs_node *node = kernfs_dentry_node(dentry);
4f41fc59 SH	48	struct kernfs_root *root = kernfs_root(node);
	49	struct kernfs_syscall_ops *scops = root->syscall_ops;
	50
	51	if (scops && scops->show_path)
	52	return scops->show_path(sf, node, root);
	53
3cc9b23c SH	54	seq_dentry(sf, dentry, " \t\n\\");
3cc9b23c SH	55	return 0;
4f41fc59 SH	56	}
4f41fc59 SH	57
f41c5934	58	const struct super_operations kernfs_sops = {
fa736a95 TH	59	.statfs = simple_statfs,
fa736a95 TH	60	.drop_inode = generic_delete_inode,
c637b8ac	61	.evict_inode = kernfs_evict_inode,
6a7fed4e TH	62
	63	.remount_fs = kernfs_sop_remount_fs,
	64	.show_options = kernfs_sop_show_options,
4f41fc59	65	.show_path = kernfs_sop_show_path,
fa736a95 TH	66	};
fa736a95 TH	67
69fd5c39 SL	68	/*
	69	* Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
	70	* number and generation
	71	*/
	72	struct kernfs_node kernfs_get_node_by_id(struct kernfs_root root,
	73	const union kernfs_node_id *id)
	74	{
	75	struct kernfs_node *kn;
	76
	77	kn = kernfs_find_and_get_node_by_ino(root, id->ino);
	78	if (!kn)
	79	return NULL;
	80	if (kn->id.generation != id->generation) {
	81	kernfs_put(kn);
	82	return NULL;
	83	}
	84	return kn;
	85	}
	86
aa818825 SL	87	static struct inode kernfs_fh_get_inode(struct super_block sb,
	88	u64 ino, u32 generation)
	89	{
	90	struct kernfs_super_info *info = kernfs_info(sb);
	91	struct inode *inode;
	92	struct kernfs_node *kn;
	93
	94	if (ino == 0)
	95	return ERR_PTR(-ESTALE);
	96
	97	kn = kernfs_find_and_get_node_by_ino(info->root, ino);
	98	if (!kn)
	99	return ERR_PTR(-ESTALE);
	100	inode = kernfs_get_inode(sb, kn);
	101	kernfs_put(kn);
ef13ecbc DC	102	if (!inode)
ef13ecbc DC	103	return ERR_PTR(-ESTALE);
aa818825 SL	104
	105	if (generation && inode->i_generation != generation) {
	106	/* we didn't find the right inode.. */
	107	iput(inode);
	108	return ERR_PTR(-ESTALE);
	109	}
	110	return inode;
	111	}
	112
	113	static struct dentry kernfs_fh_to_dentry(struct super_block sb, struct fid *fid,
	114	int fh_len, int fh_type)
	115	{
	116	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
	117	kernfs_fh_get_inode);
	118	}
	119
	120	static struct dentry kernfs_fh_to_parent(struct super_block sb, struct fid *fid,
	121	int fh_len, int fh_type)
	122	{
	123	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
	124	kernfs_fh_get_inode);
	125	}
	126
	127	static struct dentry kernfs_get_parent_dentry(struct dentry child)
	128	{
	129	struct kernfs_node *kn = kernfs_dentry_node(child);
	130
	131	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
	132	}
	133
	134	static const struct export_operations kernfs_export_ops = {
	135	.fh_to_dentry = kernfs_fh_to_dentry,
	136	.fh_to_parent = kernfs_fh_to_parent,
	137	.get_parent = kernfs_get_parent_dentry,
	138	};
	139
0c23b225 TH	140	/**
	141	* kernfs_root_from_sb - determine kernfs_root associated with a super_block
	142	* @sb: the super_block in question
	143	*
	144	* Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
	145	* %NULL is returned.
	146	*/
	147	struct kernfs_root kernfs_root_from_sb(struct super_block sb)
	148	{
	149	if (sb->s_op == &kernfs_sops)
	150	return kernfs_info(sb)->root;
	151	return NULL;
	152	}
	153
fb3c8315 AK	154	/*
	155	* find the next ancestor in the path down to @child, where @parent was the
	156	* ancestor whose descendant we want to find.
	157	*
	158	* Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
	159	* node. If @parent is b, then we return the node for c.
	160	* Passing in d as @parent is not ok.
	161	*/
	162	static struct kernfs_node find_next_ancestor(struct kernfs_node child,
	163	struct kernfs_node *parent)
	164	{
	165	if (child == parent) {
	166	pr_crit_once("BUG in find_next_ancestor: called with parent == child");
	167	return NULL;
	168	}
	169
	170	while (child->parent != parent) {
	171	if (!child->parent)
	172	return NULL;
	173	child = child->parent;
	174	}
	175
	176	return child;
	177	}
	178
	179	/**
	180	* kernfs_node_dentry - get a dentry for the given kernfs_node
	181	* @kn: kernfs_node for which a dentry is needed
	182	* @sb: the kernfs super_block
	183	*/
	184	struct dentry kernfs_node_dentry(struct kernfs_node kn,
	185	struct super_block *sb)
	186	{
	187	struct dentry *dentry;
	188	struct kernfs_node *knparent = NULL;
	189
	190	BUG_ON(sb->s_op != &kernfs_sops);
	191
	192	dentry = dget(sb->s_root);
	193
	194	/* Check if this is the root kernfs_node */
	195	if (!kn->parent)
	196	return dentry;
	197
	198	knparent = find_next_ancestor(kn, NULL);
399504e2 AV	199	if (WARN_ON(!knparent)) {
399504e2 AV	200	dput(dentry);
fb3c8315	201	return ERR_PTR(-EINVAL);
399504e2	202	}
fb3c8315 AK	203
	204	do {
	205	struct dentry *dtmp;
	206	struct kernfs_node *kntmp;
	207
	208	if (kn == knparent)
	209	return dentry;
	210	kntmp = find_next_ancestor(kn, knparent);
399504e2 AV	211	if (WARN_ON(!kntmp)) {
399504e2 AV	212	dput(dentry);
fb3c8315	213	return ERR_PTR(-EINVAL);
399504e2	214	}
779b8391 AV	215	dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
779b8391 AV	216	strlen(kntmp->name));
fb3c8315 AK	217	dput(dentry);
	218	if (IS_ERR(dtmp))
	219	return dtmp;
	220	knparent = kntmp;
	221	dentry = dtmp;
	222	} while (true);
	223	}
	224
26fc9cd2	225	static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
fa736a95	226	{
c525aadd	227	struct kernfs_super_info *info = kernfs_info(sb);
fa736a95 TH	228	struct inode *inode;
	229	struct dentry *root;
	230
7d568a83	231	info->sb = sb;
a2982cc9 EB	232	/* Userspace would break if executables or devices appear on sysfs */
a2982cc9 EB	233	sb->s_iflags \|= SB_I_NOEXEC \| SB_I_NODEV;
09cbfeaf KS	234	sb->s_blocksize = PAGE_SIZE;
09cbfeaf KS	235	sb->s_blocksize_bits = PAGE_SHIFT;
26fc9cd2	236	sb->s_magic = magic;
a797bfc3	237	sb->s_op = &kernfs_sops;
e72a1a8b	238	sb->s_xattr = kernfs_xattr_handlers;
aa818825 SL	239	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
aa818825 SL	240	sb->s_export_op = &kernfs_export_ops;
fa736a95 TH	241	sb->s_time_gran = 1;
fa736a95 TH	242
4b85afbd JW	243	/* sysfs dentries and inodes don't require IO to create */
	244	sb->s_shrink.seeks = 0;
	245
fa736a95	246	/* get root inode, initialize and unlock it */
a797bfc3	247	mutex_lock(&kernfs_mutex);
c637b8ac	248	inode = kernfs_get_inode(sb, info->root->kn);
a797bfc3	249	mutex_unlock(&kernfs_mutex);
fa736a95	250	if (!inode) {
c637b8ac	251	pr_debug("kernfs: could not get root inode\n");
fa736a95 TH	252	return -ENOMEM;
	253	}
	254
	255	/* instantiate and link root dentry */
	256	root = d_make_root(inode);
	257	if (!root) {
	258	pr_debug("%s: could not get root dentry!\n", __func__);
	259	return -ENOMEM;
	260	}
fa736a95	261	sb->s_root = root;
a797bfc3	262	sb->s_d_op = &kernfs_dops;
fa736a95 TH	263	return 0;
	264	}
	265
c637b8ac	266	static int kernfs_test_super(struct super_block sb, void data)
fa736a95	267	{
c525aadd TH	268	struct kernfs_super_info *sb_info = kernfs_info(sb);
c525aadd TH	269	struct kernfs_super_info *info = data;
fa736a95 TH	270
	271	return sb_info->root == info->root && sb_info->ns == info->ns;
	272	}
	273
c637b8ac	274	static int kernfs_set_super(struct super_block sb, void data)
fa736a95 TH	275	{
	276	int error;
	277	error = set_anon_super(sb, data);
	278	if (!error)
	279	sb->s_fs_info = data;
	280	return error;
	281	}
	282
	283	/**
	284	* kernfs_super_ns - determine the namespace tag of a kernfs super_block
	285	* @sb: super_block of interest
	286	*
	287	* Return the namespace tag associated with kernfs super_block @sb.
	288	*/
	289	const void kernfs_super_ns(struct super_block sb)
	290	{
c525aadd	291	struct kernfs_super_info *info = kernfs_info(sb);
fa736a95 TH	292
	293	return info->ns;
	294	}
	295
	296	/**
	297	* kernfs_mount_ns - kernfs mount helper
	298	* @fs_type: file_system_type of the fs being mounted
	299	* @flags: mount flags specified for the mount
	300	* @root: kernfs_root of the hierarchy being mounted
26fc9cd2	301	* @magic: file system specific magic number
fed95bab	302	* @new_sb_created: tell the caller if we allocated a new superblock
fa736a95 TH	303	* @ns: optional namespace tag of the mount
	304	*
	305	* This is to be called from each kernfs user's file_system_type->mount()
	306	* implementation, which should pass through the specified @fs_type and
	307	* @flags, and specify the hierarchy and namespace tag to mount via @root
	308	* and @ns, respectively.
	309	*
	310	* The return value can be passed to the vfs layer verbatim.
	311	*/
	312	struct dentry kernfs_mount_ns(struct file_system_type fs_type, int flags,
26fc9cd2 JZ	313	struct kernfs_root *root, unsigned long magic,
26fc9cd2 JZ	314	bool new_sb_created, const void ns)
fa736a95 TH	315	{
fa736a95 TH	316	struct super_block *sb;
c525aadd	317	struct kernfs_super_info *info;
fa736a95 TH	318	int error;
	319
	320	info = kzalloc(sizeof(*info), GFP_KERNEL);
	321	if (!info)
	322	return ERR_PTR(-ENOMEM);
	323
	324	info->root = root;
	325	info->ns = ns;
82382ace	326	INIT_LIST_HEAD(&info->node);
fa736a95	327
6e4eab57 EB	328	sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
6e4eab57 EB	329	&init_user_ns, info);
fa736a95 TH	330	if (IS_ERR(sb) \|\| sb->s_fs_info != info)
	331	kfree(info);
	332	if (IS_ERR(sb))
	333	return ERR_CAST(sb);
fed95bab LZ	334
	335	if (new_sb_created)
	336	*new_sb_created = !sb->s_root;
	337
fa736a95	338	if (!sb->s_root) {
7d568a83 TH	339	struct kernfs_super_info *info = kernfs_info(sb);
7d568a83 TH	340
26fc9cd2	341	error = kernfs_fill_super(sb, magic);
fa736a95 TH	342	if (error) {
	343	deactivate_locked_super(sb);
	344	return ERR_PTR(error);
	345	}
1751e8a6	346	sb->s_flags \|= SB_ACTIVE;
7d568a83 TH	347
	348	mutex_lock(&kernfs_mutex);
	349	list_add(&info->node, &root->supers);
	350	mutex_unlock(&kernfs_mutex);
fa736a95 TH	351	}
	352
	353	return dget(sb->s_root);
	354	}
	355
	356	/**
	357	* kernfs_kill_sb - kill_sb for kernfs
	358	* @sb: super_block being killed
	359	*
	360	* This can be used directly for file_system_type->kill_sb(). If a kernfs
	361	* user needs extra cleanup, it can implement its own kill_sb() and call
	362	* this function at the end.
	363	*/
	364	void kernfs_kill_sb(struct super_block *sb)
	365	{
c525aadd	366	struct kernfs_super_info *info = kernfs_info(sb);
fa736a95	367
7d568a83 TH	368	mutex_lock(&kernfs_mutex);
	369	list_del(&info->node);
	370	mutex_unlock(&kernfs_mutex);
	371
fa736a95 TH	372	/*
fa736a95 TH	373	* Remove the superblock from fs_supers/s_instances
c525aadd	374	* so we can't find it, before freeing kernfs_super_info.
fa736a95 TH	375	*/
	376	kill_anon_super(sb);
	377	kfree(info);
fa736a95 TH	378	}
fa736a95 TH	379
4e26445f LZ	380	/**
	381	* kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
	382	* @kernfs_root: the kernfs_root in question
	383	* @ns: the namespace tag
	384	*
	385	* Pin the superblock so the superblock won't be destroyed in subsequent
	386	* operations. This can be used to block ->kill_sb() which may be useful
	387	* for kernfs users which dynamically manage superblocks.
	388	*
	389	* Returns NULL if there's no superblock associated to this kernfs_root, or
	390	* -EINVAL if the superblock is being freed.
	391	*/
	392	struct super_block kernfs_pin_sb(struct kernfs_root root, const void *ns)
	393	{
	394	struct kernfs_super_info *info;
	395	struct super_block *sb = NULL;
	396
	397	mutex_lock(&kernfs_mutex);
	398	list_for_each_entry(info, &root->supers, node) {
	399	if (info->ns == ns) {
	400	sb = info->sb;
	401	if (!atomic_inc_not_zero(&info->sb->s_active))
	402	sb = ERR_PTR(-EINVAL);
	403	break;
	404	}
	405	}
	406	mutex_unlock(&kernfs_mutex);
	407	return sb;
	408	}
	409
fa736a95 TH	410	void __init kernfs_init(void)
fa736a95 TH	411	{
ba16b284 SL	412
	413	/*
	414	* the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
	415	* can access the slab lock free. This could introduce stale nodes,
	416	* please see how kernfs_find_and_get_node_by_ino filters out stale
	417	* nodes.
	418	*/
a797bfc3	419	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
324a56e1	420	sizeof(struct kernfs_node),
ba16b284 SL	421	0,
	422	SLAB_PANIC \| SLAB_TYPESAFE_BY_RCU,
	423	NULL);
26e28d68 AM	424
	425	/* Creates slab cache for kernfs inode attributes */
	426	kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
	427	sizeof(struct kernfs_iattrs),
	428	0, SLAB_PANIC, NULL);
fa736a95	429	}