/* * 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_CACHE_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, j; 	if (cache == NULL)		return; 	for (i = 0; i < cache->entries; i++) {		if (cache->entry[i].data) {			for (j = 0; j < cache->pages; j++)				kfree(cache->entry[i].data[j]);			kfree(cache->entry[i].data);		}		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_CACHE_SIZE buffers. */struct squashfs_cache *squashfs_cache_init(char *name, int entries,	int block_size){	int i, j;	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_CACHE_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->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);		if (entry->data == NULL) {			ERROR("Failed to allocate %s cache entry\n", name);			goto cleanup;		} 		for (j = 0; j < cache->pages; j++) {			entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);			if (entry->data[j] == NULL) {				ERROR("Failed to allocate %s buffer\n", name);				goto cleanup;			}		} 		entry->actor = squashfs_page_actor_init(entry->data,						cache->pages, 0);		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 = entry->data[offset / PAGE_CACHE_SIZE]				+ (offset % PAGE_CACHE_SIZE);		int bytes = min_t(int, entry->length - offset,				PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE)); 		if (bytes >= remaining) {			memcpy(buffer, buff, remaining);			remaining = 0;			break;		} 		memcpy(buffer, buff, bytes);		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_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;	int i, res;	void *table, *buffer, **data;	struct squashfs_page_actor *actor; 	table = buffer = kmalloc(length, GFP_KERNEL);	if (table == NULL)		return ERR_PTR(-ENOMEM); 	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);	if (data == NULL) {		res = -ENOMEM;		goto failed;	} 	actor = squashfs_page_actor_init(data, pages, length);	if (actor == NULL) {		res = -ENOMEM;		goto failed2;	} 	for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)		data[i] = buffer; 	res = squashfs_read_data(sb, block, length |		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor); 	kfree(data);	kfree(actor); 	if (res < 0)		goto failed; 	return table; failed2:	kfree(data);failed:	kfree(table);	return ERR_PTR(res);}