fs/squashfs/cache.c - kernel/msm-4.9 - Gitiles

 /*
  * Squashfs - a compressed read only filesystem for Linux
  *
  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
  * Phillip Lougher <phillip@squashfs.org.uk>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2,
  * or (at your option) any later version.
  *
  * 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, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  *
  * cache.c
  */

 /*
  * Blocks in Squashfs are compressed.  To avoid repeatedly decompressing
  * recently accessed data Squashfs uses two small metadata and fragment caches.
  *
  * This file implements a generic cache implementation used for both caches,
  * plus functions layered ontop of the generic cache implementation to
  * access the metadata and fragment caches.
  *
  * To avoid out of memory and fragmentation issues with vmalloc the cache
  * uses sequences of kmalloced PAGE_SIZE buffers.
  *
  * It should be noted that the cache is not used for file datablocks, these
  * are decompressed and cached in the page-cache in the normal way.  The
  * cache is only used to temporarily cache fragment and metadata blocks
  * which have been read as as a result of a metadata (i.e. inode or
  * directory) or fragment access.  Because metadata and fragments are packed
  * together into blocks (to gain greater compression) the read of a particular
  * piece of metadata or fragment will retrieve other metadata/fragments which
  * have been packed with it, these because of locality-of-reference may be read
  * in the near future. Temporarily caching them ensures they are available for
  * near future access without requiring an additional read and decompress.
  */

 #include <linux/fs.h>
 #include <linux/vfs.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
 #include <linux/spinlock.h>
 #include <linux/wait.h>
 #include <linux/pagemap.h>

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

 /*
  * Look-up block in cache, and increment usage count.  If not in cache, read
  * and decompress it from disk.
  */
 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
 	struct squashfs_cache *cache, u64 block, int length)
 {
 	int i, n;
 	struct squashfs_cache_entry *entry;

 	spin_lock(&cache->lock);

 	while (1) {
 		for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
 			if (cache->entry[i].block == block) {
 				cache->curr_blk = i;
 				break;
 			}
 			i = (i + 1) % cache->entries;
 		}

 		if (n == cache->entries) {
 			/*
 			 * Block not in cache, if all cache entries are used
 			 * go to sleep waiting for one to become available.
 			 */
 			if (cache->unused == 0) {
 				cache->num_waiters++;
 				spin_unlock(&cache->lock);
 				wait_event(cache->wait_queue, cache->unused);
 				spin_lock(&cache->lock);
 				cache->num_waiters--;
 				continue;
 			}

 			/*
 			 * At least one unused cache entry.  A simple
 			 * round-robin strategy is used to choose the entry to
 			 * be evicted from the cache.
 			 */
 			i = cache->next_blk;
 			for (n = 0; n < cache->entries; n++) {
 				if (cache->entry[i].refcount == 0)
 					break;
 				i = (i + 1) % cache->entries;
 			}

 			cache->next_blk = (i + 1) % cache->entries;
 			entry = &cache->entry[i];

 			/*
 			 * Initialise chosen cache entry, and fill it in from
 			 * disk.
 			 */
 			cache->unused--;
 			entry->block = block;
 			entry->refcount = 1;
 			entry->pending = 1;
 			entry->num_waiters = 0;
 			entry->error = 0;
 			spin_unlock(&cache->lock);

 			entry->length = squashfs_read_data(sb, block, length,
 				&entry->next_index, entry->actor);

 			spin_lock(&cache->lock);

 			if (entry->length < 0)
 				entry->error = entry->length;

 			entry->pending = 0;

 			/*
 			 * While filling this entry one or more other processes
 			 * have looked it up in the cache, and have slept
 			 * waiting for it to become available.
 			 */
 			if (entry->num_waiters) {
 				spin_unlock(&cache->lock);
 				wake_up_all(&entry->wait_queue);
 			} else
 				spin_unlock(&cache->lock);

 			goto out;
 		}

 		/*
 		 * Block already in cache.  Increment refcount so it doesn't
 		 * get reused until we're finished with it, if it was
 		 * previously unused there's one less cache entry available
 		 * for reuse.
 		 */
 		entry = &cache->entry[i];
 		if (entry->refcount == 0)
 			cache->unused--;
 		entry->refcount++;

 		/*
 		 * If the entry is currently being filled in by another process
 		 * go to sleep waiting for it to become available.
 		 */
 		if (entry->pending) {
 			entry->num_waiters++;
 			spin_unlock(&cache->lock);
 			wait_event(entry->wait_queue, !entry->pending);
 		} else
 			spin_unlock(&cache->lock);

 		goto out;
 	}

 out:
 	TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
 		cache->name, i, entry->block, entry->refcount, entry->error);

 	if (entry->error)
 		ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
 							block);
 	return entry;
 }


 /*
  * Release cache entry, once usage count is zero it can be reused.
  */
 void squashfs_cache_put(struct squashfs_cache_entry *entry)
 {
 	struct squashfs_cache *cache = entry->cache;

 	spin_lock(&cache->lock);
 	entry->refcount--;
 	if (entry->refcount == 0) {
 		cache->unused++;
 		/*
 		 * If there's any processes waiting for a block to become
 		 * available, wake one up.
 		 */
 		if (cache->num_waiters) {
 			spin_unlock(&cache->lock);
 			wake_up(&cache->wait_queue);
 			return;
 		}
 	}
 	spin_unlock(&cache->lock);
 }

 /*
  * Delete cache reclaiming all kmalloced buffers.
  */
 void squashfs_cache_delete(struct squashfs_cache *cache)
 {
 	int i;

 	if (cache == NULL)
 		return;

 	for (i = 0; i < cache->entries; i++) {
 		if (cache->entry[i].page)
 			free_page_array(cache->entry[i].page, cache->pages);
 		kfree(cache->entry[i].actor);
 	}

 	kfree(cache->entry);
 	kfree(cache);
 }


 /*
  * Initialise cache allocating the specified number of entries, each of
  * size block_size.  To avoid vmalloc fragmentation issues each entry
  * is allocated as a sequence of kmalloced PAGE_SIZE buffers.
  */
 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 	int block_size)
 {
 	int i;
 	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);

 	if (cache == NULL) {
 		ERROR("Failed to allocate %s cache\n", name);
 		return NULL;
 	}

 	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
 	if (cache->entry == NULL) {
 		ERROR("Failed to allocate %s cache\n", name);
 		goto cleanup;
 	}

 	cache->curr_blk = 0;
 	cache->next_blk = 0;
 	cache->unused = entries;
 	cache->entries = entries;
 	cache->block_size = block_size;
 	cache->pages = block_size >> PAGE_SHIFT;
 	cache->pages = cache->pages ? cache->pages : 1;
 	cache->name = name;
 	cache->num_waiters = 0;
 	spin_lock_init(&cache->lock);
 	init_waitqueue_head(&cache->wait_queue);

 	for (i = 0; i < entries; i++) {
 		struct squashfs_cache_entry *entry = &cache->entry[i];

 		init_waitqueue_head(&cache->entry[i].wait_queue);
 		entry->cache = cache;
 		entry->block = SQUASHFS_INVALID_BLK;
 		entry->page = alloc_page_array(cache->pages, GFP_KERNEL);
 		if (!entry->page) {
 			ERROR("Failed to allocate %s cache entry\n", name);
 			goto cleanup;
 		}
 		entry->actor = squashfs_page_actor_init(entry->page,
 			cache->pages, 0, NULL);
 		if (entry->actor == NULL) {
 			ERROR("Failed to allocate %s cache entry\n", name);
 			goto cleanup;
 		}
 	}

 	return cache;

 cleanup:
 	squashfs_cache_delete(cache);
 	return NULL;
 }


 /*
  * Copy up to length bytes from cache entry to buffer starting at offset bytes
  * into the cache entry.  If there's not length bytes then copy the number of
  * bytes available.  In all cases return the number of bytes copied.
  */
 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
 		int offset, int length)
 {
 	int remaining = length;

 	if (length == 0)
 		return 0;
 	else if (buffer == NULL)
 		return min(length, entry->length - offset);

 	while (offset < entry->length) {
 		void *buff = kmap_atomic(entry->page[offset / PAGE_SIZE])
 			     + (offset % PAGE_SIZE);
 		int bytes = min_t(int, entry->length - offset,
 				PAGE_SIZE - (offset % PAGE_SIZE));

 		if (bytes >= remaining) {
 			memcpy(buffer, buff, remaining);
 			kunmap_atomic(buff);
 			remaining = 0;
 			break;
 		}

 		memcpy(buffer, buff, bytes);
 		kunmap_atomic(buff);
 		buffer += bytes;
 		remaining -= bytes;
 		offset += bytes;
 	}

 	return length - remaining;
 }


 /*
  * Read length bytes from metadata position <block, offset> (block is the
  * start of the compressed block on disk, and offset is the offset into
  * the block once decompressed).  Data is packed into consecutive blocks,
  * and length bytes may require reading more than one block.
  */
 int squashfs_read_metadata(struct super_block *sb, void *buffer,
 		u64 *block, int *offset, int length)
 {
 	struct squashfs_sb_info *msblk = sb->s_fs_info;
 	int bytes, res = length;
 	struct squashfs_cache_entry *entry;

 	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);

 	while (length) {
 		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
 		if (entry->error) {
 			res = entry->error;
 			goto error;
 		} else if (*offset >= entry->length) {
 			res = -EIO;
 			goto error;
 		}

 		bytes = squashfs_copy_data(buffer, entry, *offset, length);
 		if (buffer)
 			buffer += bytes;
 		length -= bytes;
 		*offset += bytes;

 		if (*offset == entry->length) {
 			*block = entry->next_index;
 			*offset = 0;
 		}

 		squashfs_cache_put(entry);
 	}

 	return res;

 error:
 	squashfs_cache_put(entry);
 	return res;
 }


 /*
  * Look-up in the fragmment cache the fragment located at <start_block> in the
  * filesystem.  If necessary read and decompress it from disk.
  */
 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
 				u64 start_block, int length)
 {
 	struct squashfs_sb_info *msblk = sb->s_fs_info;

 	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
 		length);
 }


 /*
  * Read and decompress the datablock located at <start_block> in the
  * filesystem.  The cache is used here to avoid duplicating locking and
  * read/decompress code.
  */
 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
 				u64 start_block, int length)
 {
 	struct squashfs_sb_info *msblk = sb->s_fs_info;

 	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
 }


 /*
  * Read a filesystem table (uncompressed sequence of bytes) from disk
  */
 void *squashfs_read_table(struct super_block *sb, u64 block, int length)
 {
 	int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	struct page **page;
 	void *buff;
 	int res;
 	struct squashfs_page_actor *actor;

 	page = alloc_page_array(pages, GFP_KERNEL);
 	if (!page)
 		return ERR_PTR(-ENOMEM);

 	actor = squashfs_page_actor_init(page, pages, length, NULL);
 	if (actor == NULL) {
 		res = -ENOMEM;
 		goto failed;
 	}

 	res = squashfs_read_data(sb, block, length |
 		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);

 	if (res < 0)
 		goto failed2;

 	buff = kmalloc(length, GFP_KERNEL);
 	if (!buff)
 		goto failed2;
 	squashfs_actor_to_buf(actor, buff, length);
 	squashfs_page_actor_free(actor, 0);
 	free_page_array(page, pages);
 	return buff;

 failed2:
 	squashfs_page_actor_free(actor, 0);
 failed:
 	free_page_array(page, pages);
 	return ERR_PTR(res);
 }
	/*
	* Squashfs - a compressed read only filesystem for Linux
	*
	* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
	* Phillip Lougher <phillip@squashfs.org.uk>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version 2,
	* or (at your option) any later version.
	*
	* 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, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	*
	* cache.c
	*/

	/*
	* Blocks in Squashfs are compressed. To avoid repeatedly decompressing
	* recently accessed data Squashfs uses two small metadata and fragment caches.
	*
	* This file implements a generic cache implementation used for both caches,
	* plus functions layered ontop of the generic cache implementation to
	* access the metadata and fragment caches.
	*
	* To avoid out of memory and fragmentation issues with vmalloc the cache
	* uses sequences of kmalloced PAGE_SIZE buffers.
	*
	* It should be noted that the cache is not used for file datablocks, these
	* are decompressed and cached in the page-cache in the normal way. The
	* cache is only used to temporarily cache fragment and metadata blocks
	* which have been read as as a result of a metadata (i.e. inode or
	* directory) or fragment access. Because metadata and fragments are packed
	* together into blocks (to gain greater compression) the read of a particular
	* piece of metadata or fragment will retrieve other metadata/fragments which
	* have been packed with it, these because of locality-of-reference may be read
	* in the near future. Temporarily caching them ensures they are available for
	* near future access without requiring an additional read and decompress.
	*/

	#include <linux/fs.h>
	#include <linux/vfs.h>
	#include <linux/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/sched.h>
	#include <linux/spinlock.h>
	#include <linux/wait.h>
	#include <linux/pagemap.h>

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

	/*
	* Look-up block in cache, and increment usage count. If not in cache, read
	* and decompress it from disk.
	*/
	struct squashfs_cache_entry squashfs_cache_get(struct super_block sb,
	struct squashfs_cache *cache, u64 block, int length)
	{
	int i, n;
	struct squashfs_cache_entry *entry;

	spin_lock(&cache->lock);

	while (1) {
	for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
	if (cache->entry[i].block == block) {
	cache->curr_blk = i;
	break;
	}
	i = (i + 1) % cache->entries;
	}

	if (n == cache->entries) {
	/*
	* Block not in cache, if all cache entries are used
	* go to sleep waiting for one to become available.
	*/
	if (cache->unused == 0) {
	cache->num_waiters++;
	spin_unlock(&cache->lock);
	wait_event(cache->wait_queue, cache->unused);
	spin_lock(&cache->lock);
	cache->num_waiters--;
	continue;
	}

	/*
	* At least one unused cache entry. A simple
	* round-robin strategy is used to choose the entry to
	* be evicted from the cache.
	*/
	i = cache->next_blk;
	for (n = 0; n < cache->entries; n++) {
	if (cache->entry[i].refcount == 0)
	break;
	i = (i + 1) % cache->entries;
	}

	cache->next_blk = (i + 1) % cache->entries;
	entry = &cache->entry[i];

	/*
	* Initialise chosen cache entry, and fill it in from
	* disk.
	*/
	cache->unused--;
	entry->block = block;
	entry->refcount = 1;
	entry->pending = 1;
	entry->num_waiters = 0;
	entry->error = 0;
	spin_unlock(&cache->lock);

	entry->length = squashfs_read_data(sb, block, length,
	&entry->next_index, entry->actor);

	spin_lock(&cache->lock);

	if (entry->length < 0)
	entry->error = entry->length;

	entry->pending = 0;

	/*
	* While filling this entry one or more other processes
	* have looked it up in the cache, and have slept
	* waiting for it to become available.
	*/
	if (entry->num_waiters) {
	spin_unlock(&cache->lock);
	wake_up_all(&entry->wait_queue);
	} else
	spin_unlock(&cache->lock);

	goto out;
	}

	/*
	* Block already in cache. Increment refcount so it doesn't
	* get reused until we're finished with it, if it was
	* previously unused there's one less cache entry available
	* for reuse.
	*/
	entry = &cache->entry[i];
	if (entry->refcount == 0)
	cache->unused--;
	entry->refcount++;

	/*
	* If the entry is currently being filled in by another process
	* go to sleep waiting for it to become available.
	*/
	if (entry->pending) {
	entry->num_waiters++;
	spin_unlock(&cache->lock);
	wait_event(entry->wait_queue, !entry->pending);
	} else
	spin_unlock(&cache->lock);

	goto out;
	}

	out:
	TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
	cache->name, i, entry->block, entry->refcount, entry->error);

	if (entry->error)
	ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
	block);
	return entry;
	}


	/*
	* Release cache entry, once usage count is zero it can be reused.
	*/
	void squashfs_cache_put(struct squashfs_cache_entry *entry)
	{
	struct squashfs_cache *cache = entry->cache;

	spin_lock(&cache->lock);
	entry->refcount--;
	if (entry->refcount == 0) {
	cache->unused++;
	/*
	* If there's any processes waiting for a block to become
	* available, wake one up.
	*/
	if (cache->num_waiters) {
	spin_unlock(&cache->lock);
	wake_up(&cache->wait_queue);
	return;
	}
	}
	spin_unlock(&cache->lock);
	}

	/*
	* Delete cache reclaiming all kmalloced buffers.
	*/
	void squashfs_cache_delete(struct squashfs_cache *cache)
	{
	int i;

	if (cache == NULL)
	return;

	for (i = 0; i < cache->entries; i++) {
	if (cache->entry[i].page)
	free_page_array(cache->entry[i].page, cache->pages);
	kfree(cache->entry[i].actor);
	}

	kfree(cache->entry);
	kfree(cache);
	}


	/*
	* Initialise cache allocating the specified number of entries, each of
	* size block_size. To avoid vmalloc fragmentation issues each entry
	* is allocated as a sequence of kmalloced PAGE_SIZE buffers.
	*/
	struct squashfs_cache squashfs_cache_init(char name, int entries,
	int block_size)
	{
	int i;
	struct squashfs_cache cache = kzalloc(sizeof(cache), GFP_KERNEL);

	if (cache == NULL) {
	ERROR("Failed to allocate %s cache\n", name);
	return NULL;
	}

	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
	if (cache->entry == NULL) {
	ERROR("Failed to allocate %s cache\n", name);
	goto cleanup;
	}

	cache->curr_blk = 0;
	cache->next_blk = 0;
	cache->unused = entries;
	cache->entries = entries;
	cache->block_size = block_size;
	cache->pages = block_size >> PAGE_SHIFT;
	cache->pages = cache->pages ? cache->pages : 1;
	cache->name = name;
	cache->num_waiters = 0;
	spin_lock_init(&cache->lock);
	init_waitqueue_head(&cache->wait_queue);

	for (i = 0; i < entries; i++) {
	struct squashfs_cache_entry *entry = &cache->entry[i];

	init_waitqueue_head(&cache->entry[i].wait_queue);
	entry->cache = cache;
	entry->block = SQUASHFS_INVALID_BLK;
	entry->page = alloc_page_array(cache->pages, GFP_KERNEL);
	if (!entry->page) {
	ERROR("Failed to allocate %s cache entry\n", name);
	goto cleanup;
	}
	entry->actor = squashfs_page_actor_init(entry->page,
	cache->pages, 0, NULL);
	if (entry->actor == NULL) {
	ERROR("Failed to allocate %s cache entry\n", name);
	goto cleanup;
	}
	}

	return cache;

	cleanup:
	squashfs_cache_delete(cache);
	return NULL;
	}


	/*
	* Copy up to length bytes from cache entry to buffer starting at offset bytes
	* into the cache entry. If there's not length bytes then copy the number of
	* bytes available. In all cases return the number of bytes copied.
	*/
	int squashfs_copy_data(void buffer, struct squashfs_cache_entry entry,
	int offset, int length)
	{
	int remaining = length;

	if (length == 0)
	return 0;
	else if (buffer == NULL)
	return min(length, entry->length - offset);

	while (offset < entry->length) {
	void *buff = kmap_atomic(entry->page[offset / PAGE_SIZE])
	+ (offset % PAGE_SIZE);
	int bytes = min_t(int, entry->length - offset,
	PAGE_SIZE - (offset % PAGE_SIZE));

	if (bytes >= remaining) {
	memcpy(buffer, buff, remaining);
	kunmap_atomic(buff);
	remaining = 0;
	break;
	}

	memcpy(buffer, buff, bytes);
	kunmap_atomic(buff);
	buffer += bytes;
	remaining -= bytes;
	offset += bytes;
	}

	return length - remaining;
	}


	/*
	* Read length bytes from metadata position <block, offset> (block is the
	* start of the compressed block on disk, and offset is the offset into
	* the block once decompressed). Data is packed into consecutive blocks,
	* and length bytes may require reading more than one block.
	*/
	int squashfs_read_metadata(struct super_block sb, void buffer,
	u64 block, int offset, int length)
	{
	struct squashfs_sb_info *msblk = sb->s_fs_info;
	int bytes, res = length;
	struct squashfs_cache_entry *entry;

	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", block, offset);

	while (length) {
	entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
	if (entry->error) {
	res = entry->error;
	goto error;
	} else if (*offset >= entry->length) {
	res = -EIO;
	goto error;
	}

	bytes = squashfs_copy_data(buffer, entry, *offset, length);
	if (buffer)
	buffer += bytes;
	length -= bytes;
	*offset += bytes;

	if (*offset == entry->length) {
	*block = entry->next_index;
	*offset = 0;
	}

	squashfs_cache_put(entry);
	}

	return res;

	error:
	squashfs_cache_put(entry);
	return res;
	}


	/*
	* Look-up in the fragmment cache the fragment located at <start_block> in the
	* filesystem. If necessary read and decompress it from disk.
	*/
	struct squashfs_cache_entry squashfs_get_fragment(struct super_block sb,
	u64 start_block, int length)
	{
	struct squashfs_sb_info *msblk = sb->s_fs_info;

	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
	length);
	}


	/*
	* Read and decompress the datablock located at <start_block> in the
	* filesystem. The cache is used here to avoid duplicating locking and
	* read/decompress code.
	*/
	struct squashfs_cache_entry squashfs_get_datablock(struct super_block sb,
	u64 start_block, int length)
	{
	struct squashfs_sb_info *msblk = sb->s_fs_info;

	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
	}


	/*
	* Read a filesystem table (uncompressed sequence of bytes) from disk
	*/
	void squashfs_read_table(struct super_block sb, u64 block, int length)
	{
	int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
	struct page **page;
	void *buff;
	int res;
	struct squashfs_page_actor *actor;

	page = alloc_page_array(pages, GFP_KERNEL);
	if (!page)
	return ERR_PTR(-ENOMEM);

	actor = squashfs_page_actor_init(page, pages, length, NULL);
	if (actor == NULL) {
	res = -ENOMEM;
	goto failed;
	}

	res = squashfs_read_data(sb, block, length \|
	SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);

	if (res < 0)
	goto failed2;

	buff = kmalloc(length, GFP_KERNEL);
	if (!buff)
	goto failed2;
	squashfs_actor_to_buf(actor, buff, length);
	squashfs_page_actor_free(actor, 0);
	free_page_array(page, pages);
	return buff;

	failed2:
	squashfs_page_actor_free(actor, 0);
	failed:
	free_page_array(page, pages);
	return ERR_PTR(res);
	}