fs/squashfs/file.c - linux - Git at Google

 // 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 <phillip@squashfs.org.uk>
  *
  * 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
 };
	// 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 <phillip@squashfs.org.uk>
	*
	* 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
	};