diff options
| -rw-r--r-- | fs/squashfs/cache.c | 412 |
1 files changed, 412 insertions, 0 deletions
diff --git a/fs/squashfs/cache.c b/fs/squashfs/cache.c new file mode 100644 index 00000000000..f29eda16d25 --- /dev/null +++ b/fs/squashfs/cache.c @@ -0,0 +1,412 @@ +/* + * Squashfs - a compressed read only filesystem for Linux + * + * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 + * Phillip Lougher <phillip@lougher.demon.co.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 isssues 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/zlib.h> +#include <linux/pagemap.h> + +#include "squashfs_fs.h" +#include "squashfs_fs_sb.h" +#include "squashfs_fs_i.h" +#include "squashfs.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 = 0; i < cache->entries; i++) + if (cache->entry[i].block == block) + break; + + if (i == 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 choosen 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, entry->data, + block, length, &entry->next_index, + cache->block_size); + + 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); + 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->next_blk = 0; + cache->unused = entries; + cache->entries = entries; + cache->block_size = block_size; + cache->pages = block_size >> PAGE_CACHE_SHIFT; + 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; + } + } + } + + return cache; + +cleanup: + squashfs_cache_delete(cache); + return NULL; +} + + +/* + * Copy upto 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, copied = 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) + return entry->error; + else if (*offset >= entry->length) + return -EIO; + + 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 copied; +} + + +/* + * 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 + */ +int squashfs_read_table(struct super_block *sb, void *buffer, u64 block, + int length) +{ + int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; + int i, res; + void **data = kcalloc(pages, sizeof(void *), GFP_KERNEL); + if (data == NULL) + return -ENOMEM; + + for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE) + data[i] = buffer; + res = squashfs_read_data(sb, data, block, length | + SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length); + kfree(data); + return res; +} |