[linux.git] / fs / squashfs / file.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <[email protected]>
 *
 * file.c
 */

/*
 * This file contains code for handling regular files.  A regular file
 * consists of a sequence of contiguous compressed blocks, and/or a
 * compressed fragment block (tail-end packed block).   The compressed size
 * of each datablock is stored in a block list contained within the
 * file inode (itself stored in one or more compressed metadata blocks).
 *
 * To speed up access to datablocks when reading 'large' files (256 Mbytes or
 * larger), the code implements an index cache that caches the mapping from
 * block index to datablock location on disk.
 *
 * The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
 * retaining a simple and space-efficient block list on disk.  The cache
 * is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
 * Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
 * The index cache is designed to be memory efficient, and by default uses
 * 16 KiB.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/pagemap.h>
#include <linux/mutex.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"

/*
 * Locate cache slot in range [offset, index] for specified inode.  If
 * there's more than one return the slot closest to index.
 */
static struct meta_index *locate_meta_index(struct inode *inode, int offset,
				int index)
{
	struct meta_index *meta = NULL;
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	int i;

	mutex_lock(&msblk->meta_index_mutex);

	TRACE("locate_meta_index: index %d, offset %d\n", index, offset);

	if (msblk->meta_index == NULL)
		goto not_allocated;

	for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
		if (msblk->meta_index[i].inode_number == inode->i_ino &&
				msblk->meta_index[i].offset >= offset &&
				msblk->meta_index[i].offset <= index &&
				msblk->meta_index[i].locked == 0) {
			TRACE("locate_meta_index: entry %d, offset %d\n", i,
					msblk->meta_index[i].offset);
			meta = &msblk->meta_index[i];
			offset = meta->offset;
		}
	}

	if (meta)
		meta->locked = 1;

not_allocated:
	mutex_unlock(&msblk->meta_index_mutex);

	return meta;
}


/*
 * Find and initialise an empty cache slot for index offset.
 */
static struct meta_index *empty_meta_index(struct inode *inode, int offset,
				int skip)
{
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	struct meta_index *meta = NULL;
	int i;

	mutex_lock(&msblk->meta_index_mutex);

	TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);

	if (msblk->meta_index == NULL) {
		/*
		 * First time cache index has been used, allocate and
		 * initialise.  The cache index could be allocated at
		 * mount time but doing it here means it is allocated only
		 * if a 'large' file is read.
		 */
		msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
			sizeof(*(msblk->meta_index)), GFP_KERNEL);
		if (msblk->meta_index == NULL) {
			ERROR("Failed to allocate meta_index\n");
			goto failed;
		}
		for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
			msblk->meta_index[i].inode_number = 0;
			msblk->meta_index[i].locked = 0;
		}
		msblk->next_meta_index = 0;
	}

	for (i = SQUASHFS_META_SLOTS; i &&
			msblk->meta_index[msblk->next_meta_index].locked; i--)
		msblk->next_meta_index = (msblk->next_meta_index + 1) %
			SQUASHFS_META_SLOTS;

	if (i == 0) {
		TRACE("empty_meta_index: failed!\n");
		goto failed;
	}

	TRACE("empty_meta_index: returned meta entry %d, %p\n",
			msblk->next_meta_index,
			&msblk->meta_index[msblk->next_meta_index]);

	meta = &msblk->meta_index[msblk->next_meta_index];
	msblk->next_meta_index = (msblk->next_meta_index + 1) %
			SQUASHFS_META_SLOTS;

	meta->inode_number = inode->i_ino;
	meta->offset = offset;
	meta->skip = skip;
	meta->entries = 0;
	meta->locked = 1;

failed:
	mutex_unlock(&msblk->meta_index_mutex);
	return meta;
}


static void release_meta_index(struct inode *inode, struct meta_index *meta)
{
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	mutex_lock(&msblk->meta_index_mutex);
	meta->locked = 0;
	mutex_unlock(&msblk->meta_index_mutex);
}


/*
 * Read the next n blocks from the block list, starting from
 * metadata block <start_block, offset>.
 */
static long long read_indexes(struct super_block *sb, int n,
				u64 *start_block, int *offset)
{
	int err, i;
	long long block = 0;
	__le32 *blist = kmalloc(PAGE_SIZE, GFP_KERNEL);

	if (blist == NULL) {
		ERROR("read_indexes: Failed to allocate block_list\n");
		return -ENOMEM;
	}

	while (n) {
		int blocks = min_t(int, n, PAGE_SIZE >> 2);

		err = squashfs_read_metadata(sb, blist, start_block,
				offset, blocks << 2);
		if (err < 0) {
			ERROR("read_indexes: reading block [%llx:%x]\n",
				*start_block, *offset);
			goto failure;
		}

		for (i = 0; i < blocks; i++) {
			int size = squashfs_block_size(blist[i]);
			if (size < 0) {
				err = size;
				goto failure;
			}
			block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
		}
		n -= blocks;
	}

	kfree(blist);
	return block;

failure:
	kfree(blist);
	return err;
}


/*
 * Each cache index slot has SQUASHFS_META_ENTRIES, each of which
 * can cache one index -> datablock/blocklist-block mapping.  We wish
 * to distribute these over the length of the file, entry[0] maps index x,
 * entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
 * The larger the file, the greater the skip factor.  The skip factor is
 * limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
 * the number of metadata blocks that need to be read fits into the cache.
 * If the skip factor is limited in this way then the file will use multiple
 * slots.
 */
static inline int calculate_skip(u64 blocks)
{
	u64 skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
		 * SQUASHFS_META_INDEXES);
	return min((u64) SQUASHFS_CACHED_BLKS - 1, skip + 1);
}


/*
 * Search and grow the index cache for the specified inode, returning the
 * on-disk locations of the datablock and block list metadata block
 * <index_block, index_offset> for index (scaled to nearest cache index).
 */
static int fill_meta_index(struct inode *inode, int index,
		u64 *index_block, int *index_offset, u64 *data_block)
{
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
	int offset = 0;
	struct meta_index *meta;
	struct meta_entry *meta_entry;
	u64 cur_index_block = squashfs_i(inode)->block_list_start;
	int cur_offset = squashfs_i(inode)->offset;
	u64 cur_data_block = squashfs_i(inode)->start;
	int err, i;

	/*
	 * Scale index to cache index (cache slot entry)
	 */
	index /= SQUASHFS_META_INDEXES * skip;

	while (offset < index) {
		meta = locate_meta_index(inode, offset + 1, index);

		if (meta == NULL) {
			meta = empty_meta_index(inode, offset + 1, skip);
			if (meta == NULL)
				goto all_done;
		} else {
			offset = index < meta->offset + meta->entries ? index :
				meta->offset + meta->entries - 1;
			meta_entry = &meta->meta_entry[offset - meta->offset];
			cur_index_block = meta_entry->index_block +
				msblk->inode_table;
			cur_offset = meta_entry->offset;
			cur_data_block = meta_entry->data_block;
			TRACE("get_meta_index: offset %d, meta->offset %d, "
				"meta->entries %d\n", offset, meta->offset,
				meta->entries);
			TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
				" data_block 0x%llx\n", cur_index_block,
				cur_offset, cur_data_block);
		}

		/*
		 * If necessary grow cache slot by reading block list.  Cache
		 * slot is extended up to index or to the end of the slot, in
		 * which case further slots will be used.
		 */
		for (i = meta->offset + meta->entries; i <= index &&
				i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
			int blocks = skip * SQUASHFS_META_INDEXES;
			long long res = read_indexes(inode->i_sb, blocks,
					&cur_index_block, &cur_offset);

			if (res < 0) {
				if (meta->entries == 0)
					/*
					 * Don't leave an empty slot on read
					 * error allocated to this inode...
					 */
					meta->inode_number = 0;
				err = res;
				goto failed;
			}

			cur_data_block += res;
			meta_entry = &meta->meta_entry[i - meta->offset];
			meta_entry->index_block = cur_index_block -
				msblk->inode_table;
			meta_entry->offset = cur_offset;
			meta_entry->data_block = cur_data_block;
			meta->entries++;
			offset++;
		}

		TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
				meta->offset, meta->entries);

		release_meta_index(inode, meta);
	}

all_done:
	*index_block = cur_index_block;
	*index_offset = cur_offset;
	*data_block = cur_data_block;

	/*
	 * Scale cache index (cache slot entry) to index
	 */
	return offset * SQUASHFS_META_INDEXES * skip;

failed:
	release_meta_index(inode, meta);
	return err;
}


/*
 * Get the on-disk location and compressed size of the datablock
 * specified by index.  Fill_meta_index() does most of the work.
 */
static int read_blocklist(struct inode *inode, int index, u64 *block)
{
	u64 start;
	long long blks;
	int offset;
	__le32 size;
	int res = fill_meta_index(inode, index, &start, &offset, block);

	TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
		       " 0x%x, block 0x%llx\n", res, index, start, offset,
			*block);

	if (res < 0)
		return res;

	/*
	 * res contains the index of the mapping returned by fill_meta_index(),
	 * this will likely be less than the desired index (because the
	 * meta_index cache works at a higher granularity).  Read any
	 * extra block indexes needed.
	 */
	if (res < index) {
		blks = read_indexes(inode->i_sb, index - res, &start, &offset);
		if (blks < 0)
			return (int) blks;
		*block += blks;
	}

	/*
	 * Read length of block specified by index.
	 */
	res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
			sizeof(size));
	if (res < 0)
		return res;
	return squashfs_block_size(size);
}

void squashfs_fill_page(struct page *page, struct squashfs_cache_entry *buffer, int offset, int avail)
{
	int copied;
	void *pageaddr;

	pageaddr = kmap_atomic(page);
	copied = squashfs_copy_data(pageaddr, buffer, offset, avail);
	memset(pageaddr + copied, 0, PAGE_SIZE - copied);
	kunmap_atomic(pageaddr);

	flush_dcache_page(page);
	if (copied == avail)
		SetPageUptodate(page);
	else
		SetPageError(page);
}

/* Copy data into page cache  */
void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer,
	int bytes, int offset)
{
	struct inode *inode = page->mapping->host;
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	int i, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
	int start_index = page->index & ~mask, end_index = start_index | mask;

	/*
	 * Loop copying datablock into pages.  As the datablock likely covers
	 * many PAGE_SIZE pages (default block size is 128 KiB) explicitly
	 * grab the pages from the page cache, except for the page that we've
	 * been called to fill.
	 */
	for (i = start_index; i <= end_index && bytes > 0; i++,
			bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
		struct page *push_page;
		int avail = buffer ? min_t(int, bytes, PAGE_SIZE) : 0;

		TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);

		push_page = (i == page->index) ? page :
			grab_cache_page_nowait(page->mapping, i);

		if (!push_page)
			continue;

		if (PageUptodate(push_page))
			goto skip_page;

		squashfs_fill_page(push_page, buffer, offset, avail);
skip_page:
		unlock_page(push_page);
		if (i != page->index)
			put_page(push_page);
	}
}

/* Read datablock stored packed inside a fragment (tail-end packed block) */
static int squashfs_readpage_fragment(struct page *page, int expected)
{
	struct inode *inode = page->mapping->host;
	struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
		squashfs_i(inode)->fragment_block,
		squashfs_i(inode)->fragment_size);
	int res = buffer->error;

	if (res)
		ERROR("Unable to read page, block %llx, size %x\n",
			squashfs_i(inode)->fragment_block,
			squashfs_i(inode)->fragment_size);
	else
		squashfs_copy_cache(page, buffer, expected,
			squashfs_i(inode)->fragment_offset);

	squashfs_cache_put(buffer);
	return res;
}

static int squashfs_readpage_sparse(struct page *page, int expected)
{
	squashfs_copy_cache(page, NULL, expected, 0);
	return 0;
}

static int squashfs_readpage(struct file *file, struct page *page)
{
	struct inode *inode = page->mapping->host;
	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	int index = page->index >> (msblk->block_log - PAGE_SHIFT);
	int file_end = i_size_read(inode) >> msblk->block_log;
	int expected = index == file_end ?
			(i_size_read(inode) & (msblk->block_size - 1)) :
			 msblk->block_size;
	int res;
	void *pageaddr;

	TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
				page->index, squashfs_i(inode)->start);

	if (page->index >= ((i_size_read(inode) + PAGE_SIZE - 1) >>
					PAGE_SHIFT))
		goto out;

	if (index < file_end || squashfs_i(inode)->fragment_block ==
					SQUASHFS_INVALID_BLK) {
		u64 block = 0;
		int bsize = read_blocklist(inode, index, &block);
		if (bsize < 0)
			goto error_out;

		if (bsize == 0)
			res = squashfs_readpage_sparse(page, expected);
		else
			res = squashfs_readpage_block(page, block, bsize, expected);
	} else
		res = squashfs_readpage_fragment(page, expected);

	if (!res)
		return 0;

error_out:
	SetPageError(page);
out:
	pageaddr = kmap_atomic(page);
	memset(pageaddr, 0, PAGE_SIZE);
	kunmap_atomic(pageaddr);
	flush_dcache_page(page);
	if (!PageError(page))
		SetPageUptodate(page);
	unlock_page(page);

	return 0;
}


const struct address_space_operations squashfs_aops = {
	.readpage = squashfs_readpage
};
Commit	Line	Data
68252eb5	1	// SPDX-License-Identifier: GPL-2.0-or-later
1701aecb PL	2	/*
	3	* Squashfs - a compressed read only filesystem for Linux
	4	*
	5	* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
d7f2ff67	6	* Phillip Lougher <[email protected]>
1701aecb	7	*
1701aecb PL	8	* file.c
	9	*/
	10
	11	/*
	12	* This file contains code for handling regular files. A regular file
	13	* consists of a sequence of contiguous compressed blocks, and/or a
	14	* compressed fragment block (tail-end packed block). The compressed size
	15	* of each datablock is stored in a block list contained within the
	16	* file inode (itself stored in one or more compressed metadata blocks).
	17	*
	18	* To speed up access to datablocks when reading 'large' files (256 Mbytes or
	19	* larger), the code implements an index cache that caches the mapping from
	20	* block index to datablock location on disk.
	21	*
	22	* The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
	23	* retaining a simple and space-efficient block list on disk. The cache
	24	* is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
	25	* Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
	26	* The index cache is designed to be memory efficient, and by default uses
	27	* 16 KiB.
	28	*/
	29
	30	#include <linux/fs.h>
	31	#include <linux/vfs.h>
	32	#include <linux/kernel.h>
	33	#include <linux/slab.h>
	34	#include <linux/string.h>
	35	#include <linux/pagemap.h>
	36	#include <linux/mutex.h>
1701aecb PL	37
	38	#include "squashfs_fs.h"
	39	#include "squashfs_fs_sb.h"
	40	#include "squashfs_fs_i.h"
	41	#include "squashfs.h"
	42
	43	/*
	44	* Locate cache slot in range [offset, index] for specified inode. If
	45	* there's more than one return the slot closest to index.
	46	*/
	47	static struct meta_index locate_meta_index(struct inode inode, int offset,
	48	int index)
	49	{
	50	struct meta_index *meta = NULL;
	51	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	52	int i;
	53
	54	mutex_lock(&msblk->meta_index_mutex);
	55
	56	TRACE("locate_meta_index: index %d, offset %d\n", index, offset);
	57
	58	if (msblk->meta_index == NULL)
	59	goto not_allocated;
	60
	61	for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
	62	if (msblk->meta_index[i].inode_number == inode->i_ino &&
	63	msblk->meta_index[i].offset >= offset &&
	64	msblk->meta_index[i].offset <= index &&
	65	msblk->meta_index[i].locked == 0) {
	66	TRACE("locate_meta_index: entry %d, offset %d\n", i,
	67	msblk->meta_index[i].offset);
	68	meta = &msblk->meta_index[i];
	69	offset = meta->offset;
	70	}
	71	}
	72
	73	if (meta)
	74	meta->locked = 1;
	75
	76	not_allocated:
	77	mutex_unlock(&msblk->meta_index_mutex);
	78
	79	return meta;
	80	}
	81
	82
	83	/*
	84	* Find and initialise an empty cache slot for index offset.
	85	*/
	86	static struct meta_index empty_meta_index(struct inode inode, int offset,
	87	int skip)
	88	{
	89	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	90	struct meta_index *meta = NULL;
	91	int i;
	92
	93	mutex_lock(&msblk->meta_index_mutex);
	94
	95	TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);
	96
	97	if (msblk->meta_index == NULL) {
	98	/*
	99	* First time cache index has been used, allocate and
	100	* initialise. The cache index could be allocated at
101	* mount time but doing it here means it is allocated only
102	* if a 'large' file is read.
103	*/
104	msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
105	sizeof(*(msblk->meta_index)), GFP_KERNEL);
106	if (msblk->meta_index == NULL) {
107	ERROR("Failed to allocate meta_index\n");
108	goto failed;
109	}
110	for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
111	msblk->meta_index[i].inode_number = 0;
112	msblk->meta_index[i].locked = 0;
113	}
114	msblk->next_meta_index = 0;
115	}
116
117	for (i = SQUASHFS_META_SLOTS; i &&
118	msblk->meta_index[msblk->next_meta_index].locked; i--)
119	msblk->next_meta_index = (msblk->next_meta_index + 1) %
120	SQUASHFS_META_SLOTS;
121
122	if (i == 0) {
123	TRACE("empty_meta_index: failed!\n");
124	goto failed;
125	}
126
127	TRACE("empty_meta_index: returned meta entry %d, %p\n",
128	msblk->next_meta_index,
129	&msblk->meta_index[msblk->next_meta_index]);
130
131	meta = &msblk->meta_index[msblk->next_meta_index];
132	msblk->next_meta_index = (msblk->next_meta_index + 1) %
133	SQUASHFS_META_SLOTS;
134
135	meta->inode_number = inode->i_ino;
136	meta->offset = offset;
137	meta->skip = skip;
138	meta->entries = 0;
139	meta->locked = 1;
140
141	failed:
142	mutex_unlock(&msblk->meta_index_mutex);
143	return meta;
144	}
145
146
147	static void release_meta_index(struct inode inode, struct meta_index meta)
148	{
149	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
150	mutex_lock(&msblk->meta_index_mutex);
151	meta->locked = 0;
152	mutex_unlock(&msblk->meta_index_mutex);
153	}
154
155
156	/*
157	* Read the next n blocks from the block list, starting from
158	* metadata block <start_block, offset>.
159	*/
160	static long long read_indexes(struct super_block *sb, int n,
161	u64 start_block, int offset)
162	{
163	int err, i;
164	long long block = 0;
09cbfeaf	165	__le32 *blist = kmalloc(PAGE_SIZE, GFP_KERNEL);
1701aecb PL	166
	167	if (blist == NULL) {
	168	ERROR("read_indexes: Failed to allocate block_list\n");
	169	return -ENOMEM;
	170	}
	171
	172	while (n) {
09cbfeaf	173	int blocks = min_t(int, n, PAGE_SIZE >> 2);
1701aecb PL	174
	175	err = squashfs_read_metadata(sb, blist, start_block,
	176	offset, blocks << 2);
	177	if (err < 0) {
	178	ERROR("read_indexes: reading block [%llx:%x]\n",
	179	start_block, offset);
	180	goto failure;
	181	}
	182
	183	for (i = 0; i < blocks; i++) {
01cfb793 LT	184	int size = squashfs_block_size(blist[i]);
	185	if (size < 0) {
	186	err = size;
	187	goto failure;
	188	}
1701aecb PL	189	block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
	190	}
	191	n -= blocks;
	192	}
	193
	194	kfree(blist);
	195	return block;
	196
	197	failure:
	198	kfree(blist);
	199	return err;
	200	}
	201
	202
	203	/*
	204	* Each cache index slot has SQUASHFS_META_ENTRIES, each of which
	205	* can cache one index -> datablock/blocklist-block mapping. We wish
	206	* to distribute these over the length of the file, entry[0] maps index x,
	207	* entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
	208	* The larger the file, the greater the skip factor. The skip factor is
	209	* limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
	210	* the number of metadata blocks that need to be read fits into the cache.
	211	* If the skip factor is limited in this way then the file will use multiple
	212	* slots.
	213	*/
d6e621de	214	static inline int calculate_skip(u64 blocks)
1701aecb	215	{
d6e621de	216	u64 skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
1701aecb	217	* SQUASHFS_META_INDEXES);
d6e621de	218	return min((u64) SQUASHFS_CACHED_BLKS - 1, skip + 1);
1701aecb PL	219	}
	220
	221
	222	/*
	223	* Search and grow the index cache for the specified inode, returning the
	224	* on-disk locations of the datablock and block list metadata block
	225	* <index_block, index_offset> for index (scaled to nearest cache index).
	226	*/
	227	static int fill_meta_index(struct inode *inode, int index,
	228	u64 index_block, int index_offset, u64 *data_block)
	229	{
	230	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
	231	int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
	232	int offset = 0;
	233	struct meta_index *meta;
	234	struct meta_entry *meta_entry;
	235	u64 cur_index_block = squashfs_i(inode)->block_list_start;
	236	int cur_offset = squashfs_i(inode)->offset;
	237	u64 cur_data_block = squashfs_i(inode)->start;
	238	int err, i;
	239
	240	/*
	241	* Scale index to cache index (cache slot entry)
	242	*/
	243	index /= SQUASHFS_META_INDEXES * skip;
	244
	245	while (offset < index) {
	246	meta = locate_meta_index(inode, offset + 1, index);
	247
	248	if (meta == NULL) {
	249	meta = empty_meta_index(inode, offset + 1, skip);
	250	if (meta == NULL)
	251	goto all_done;
	252	} else {
	253	offset = index < meta->offset + meta->entries ? index :
	254	meta->offset + meta->entries - 1;
	255	meta_entry = &meta->meta_entry[offset - meta->offset];
	256	cur_index_block = meta_entry->index_block +
	257	msblk->inode_table;
	258	cur_offset = meta_entry->offset;
	259	cur_data_block = meta_entry->data_block;
	260	TRACE("get_meta_index: offset %d, meta->offset %d, "
	261	"meta->entries %d\n", offset, meta->offset,
	262	meta->entries);
	263	TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
	264	" data_block 0x%llx\n", cur_index_block,
	265	cur_offset, cur_data_block);
	266	}
	267
	268	/*
	269	* If necessary grow cache slot by reading block list. Cache
	270	* slot is extended up to index or to the end of the slot, in
	271	* which case further slots will be used.
	272	*/
	273	for (i = meta->offset + meta->entries; i <= index &&
	274	i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
	275	int blocks = skip * SQUASHFS_META_INDEXES;
	276	long long res = read_indexes(inode->i_sb, blocks,
	277	&cur_index_block, &cur_offset);
	278
	279	if (res < 0) {
	280	if (meta->entries == 0)
	281	/*
	282	* Don't leave an empty slot on read
283	* error allocated to this inode...
284	*/
285	meta->inode_number = 0;
286	err = res;
287	goto failed;
288	}
289
290	cur_data_block += res;
291	meta_entry = &meta->meta_entry[i - meta->offset];
292	meta_entry->index_block = cur_index_block -
293	msblk->inode_table;
294	meta_entry->offset = cur_offset;
295	meta_entry->data_block = cur_data_block;
296	meta->entries++;
297	offset++;
298	}
299
300	TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
301	meta->offset, meta->entries);
302
303	release_meta_index(inode, meta);
304	}
305
306	all_done:
307	*index_block = cur_index_block;
308	*index_offset = cur_offset;
309	*data_block = cur_data_block;
310
311	/*
312	* Scale cache index (cache slot entry) to index
313	*/
314	return offset * SQUASHFS_META_INDEXES * skip;
315
316	failed:
317	release_meta_index(inode, meta);
318	return err;
319	}
320
321
322	/*
323	* Get the on-disk location and compressed size of the datablock
324	* specified by index. Fill_meta_index() does most of the work.
325	*/
326	static int read_blocklist(struct inode inode, int index, u64 block)
327	{
328	u64 start;
329	long long blks;
330	int offset;
331	__le32 size;
332	int res = fill_meta_index(inode, index, &start, &offset, block);
333
334	TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
335	" 0x%x, block 0x%llx\n", res, index, start, offset,
336	*block);
337
338	if (res < 0)
339	return res;
340
341	/*
342	* res contains the index of the mapping returned by fill_meta_index(),
343	* this will likely be less than the desired index (because the
344	* meta_index cache works at a higher granularity). Read any
345	* extra block indexes needed.
346	*/
347	if (res < index) {
348	blks = read_indexes(inode->i_sb, index - res, &start, &offset);
349	if (blks < 0)
350	return (int) blks;
351	*block += blks;
352	}
353
354	/*
355	* Read length of block specified by index.
356	*/
357	res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
358	sizeof(size));
359	if (res < 0)
360	return res;
01cfb793	361	return squashfs_block_size(size);
1701aecb PL	362	}
1701aecb PL	363
cdbb65c4 LT	364	void squashfs_fill_page(struct page page, struct squashfs_cache_entry buffer, int offset, int avail)
	365	{
	366	int copied;
	367	void *pageaddr;
	368
	369	pageaddr = kmap_atomic(page);
	370	copied = squashfs_copy_data(pageaddr, buffer, offset, avail);
	371	memset(pageaddr + copied, 0, PAGE_SIZE - copied);
	372	kunmap_atomic(pageaddr);
	373
	374	flush_dcache_page(page);
	375	if (copied == avail)
	376	SetPageUptodate(page);
	377	else
	378	SetPageError(page);
	379	}
	380
5f55dbc0 PL	381	/* Copy data into page cache */
	382	void squashfs_copy_cache(struct page page, struct squashfs_cache_entry buffer,
	383	int bytes, int offset)
1701aecb PL	384	{
	385	struct inode *inode = page->mapping->host;
	386	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
09cbfeaf	387	int i, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
5f55dbc0	388	int start_index = page->index & ~mask, end_index = start_index \| mask;
1701aecb PL	389
	390	/*
	391	* Loop copying datablock into pages. As the datablock likely covers
ea1754a0	392	* many PAGE_SIZE pages (default block size is 128 KiB) explicitly
1701aecb PL	393	* grab the pages from the page cache, except for the page that we've
	394	* been called to fill.
	395	*/
	396	for (i = start_index; i <= end_index && bytes > 0; i++,
09cbfeaf	397	bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
1701aecb	398	struct page *push_page;
09cbfeaf	399	int avail = buffer ? min_t(int, bytes, PAGE_SIZE) : 0;
1701aecb PL	400
	401	TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);
	402
	403	push_page = (i == page->index) ? page :
	404	grab_cache_page_nowait(page->mapping, i);
	405
	406	if (!push_page)
	407	continue;
	408
	409	if (PageUptodate(push_page))
	410	goto skip_page;
	411
cdbb65c4	412	squashfs_fill_page(push_page, buffer, offset, avail);
1701aecb PL	413	skip_page:
	414	unlock_page(push_page);
	415	if (i != page->index)
09cbfeaf	416	put_page(push_page);
1701aecb	417	}
5f55dbc0 PL	418	}
	419
	420	/* Read datablock stored packed inside a fragment (tail-end packed block) */
a3f94cb9	421	static int squashfs_readpage_fragment(struct page *page, int expected)
5f55dbc0 PL	422	{
5f55dbc0 PL	423	struct inode *inode = page->mapping->host;
5f55dbc0 PL	424	struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
	425	squashfs_i(inode)->fragment_block,
	426	squashfs_i(inode)->fragment_size);
	427	int res = buffer->error;
	428
	429	if (res)
	430	ERROR("Unable to read page, block %llx, size %x\n",
	431	squashfs_i(inode)->fragment_block,
	432	squashfs_i(inode)->fragment_size);
	433	else
a3f94cb9	434	squashfs_copy_cache(page, buffer, expected,
5f55dbc0 PL	435	squashfs_i(inode)->fragment_offset);
	436
	437	squashfs_cache_put(buffer);
	438	return res;
	439	}
1701aecb	440
a3f94cb9	441	static int squashfs_readpage_sparse(struct page *page, int expected)
5f55dbc0	442	{
a3f94cb9	443	squashfs_copy_cache(page, NULL, expected, 0);
1701aecb	444	return 0;
5f55dbc0 PL	445	}
	446
	447	static int squashfs_readpage(struct file file, struct page page)
	448	{
	449	struct inode *inode = page->mapping->host;
	450	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
09cbfeaf	451	int index = page->index >> (msblk->block_log - PAGE_SHIFT);
5f55dbc0	452	int file_end = i_size_read(inode) >> msblk->block_log;
a3f94cb9 PL	453	int expected = index == file_end ?
	454	(i_size_read(inode) & (msblk->block_size - 1)) :
	455	msblk->block_size;
5f55dbc0 PL	456	int res;
	457	void *pageaddr;
	458
	459	TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
	460	page->index, squashfs_i(inode)->start);
	461
09cbfeaf KS	462	if (page->index >= ((i_size_read(inode) + PAGE_SIZE - 1) >>
09cbfeaf KS	463	PAGE_SHIFT))
5f55dbc0 PL	464	goto out;
	465
	466	if (index < file_end \|\| squashfs_i(inode)->fragment_block ==
	467	SQUASHFS_INVALID_BLK) {
	468	u64 block = 0;
	469	int bsize = read_blocklist(inode, index, &block);
	470	if (bsize < 0)
	471	goto error_out;
	472
	473	if (bsize == 0)
a3f94cb9	474	res = squashfs_readpage_sparse(page, expected);
5f55dbc0	475	else
a3f94cb9	476	res = squashfs_readpage_block(page, block, bsize, expected);
5f55dbc0	477	} else
a3f94cb9	478	res = squashfs_readpage_fragment(page, expected);
5f55dbc0 PL	479
	480	if (!res)
	481	return 0;
1701aecb PL	482
	483	error_out:
	484	SetPageError(page);
	485	out:
53b55e55	486	pageaddr = kmap_atomic(page);
09cbfeaf	487	memset(pageaddr, 0, PAGE_SIZE);
53b55e55	488	kunmap_atomic(pageaddr);
1701aecb PL	489	flush_dcache_page(page);
	490	if (!PageError(page))
	491	SetPageUptodate(page);
	492	unlock_page(page);
	493
	494	return 0;
	495	}
	496
	497
	498	const struct address_space_operations squashfs_aops = {
	499	.readpage = squashfs_readpage
	500	};