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448 lines
11 KiB
448 lines
11 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* Squashfs - a compressed read only filesystem for Linux |
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* |
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* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 |
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* Phillip Lougher <[email protected]> |
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* |
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* cache.c |
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*/ |
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|
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/* |
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* Blocks in Squashfs are compressed. To avoid repeatedly decompressing |
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* recently accessed data Squashfs uses two small metadata and fragment caches. |
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* |
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* This file implements a generic cache implementation used for both caches, |
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* plus functions layered ontop of the generic cache implementation to |
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* access the metadata and fragment caches. |
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* |
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* To avoid out of memory and fragmentation issues with vmalloc the cache |
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* uses sequences of kmalloced PAGE_SIZE buffers. |
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* |
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* It should be noted that the cache is not used for file datablocks, these |
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* are decompressed and cached in the page-cache in the normal way. The |
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* cache is only used to temporarily cache fragment and metadata blocks |
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* which have been read as as a result of a metadata (i.e. inode or |
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* directory) or fragment access. Because metadata and fragments are packed |
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* together into blocks (to gain greater compression) the read of a particular |
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* piece of metadata or fragment will retrieve other metadata/fragments which |
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* have been packed with it, these because of locality-of-reference may be read |
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* in the near future. Temporarily caching them ensures they are available for |
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* near future access without requiring an additional read and decompress. |
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*/ |
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#include <linux/fs.h> |
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#include <linux/vfs.h> |
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#include <linux/slab.h> |
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#include <linux/vmalloc.h> |
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#include <linux/sched.h> |
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#include <linux/spinlock.h> |
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#include <linux/wait.h> |
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#include <linux/pagemap.h> |
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#include "squashfs_fs.h" |
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#include "squashfs_fs_sb.h" |
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#include "squashfs.h" |
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#include "page_actor.h" |
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/* |
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* Look-up block in cache, and increment usage count. If not in cache, read |
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* and decompress it from disk. |
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*/ |
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struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb, |
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struct squashfs_cache *cache, u64 block, int length) |
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{ |
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int i, n; |
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struct squashfs_cache_entry *entry; |
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spin_lock(&cache->lock); |
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while (1) { |
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for (i = cache->curr_blk, n = 0; n < cache->entries; n++) { |
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if (cache->entry[i].block == block) { |
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cache->curr_blk = i; |
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break; |
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} |
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i = (i + 1) % cache->entries; |
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} |
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if (n == cache->entries) { |
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/* |
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* Block not in cache, if all cache entries are used |
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* go to sleep waiting for one to become available. |
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*/ |
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if (cache->unused == 0) { |
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cache->num_waiters++; |
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spin_unlock(&cache->lock); |
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wait_event(cache->wait_queue, cache->unused); |
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spin_lock(&cache->lock); |
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cache->num_waiters--; |
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continue; |
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} |
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/* |
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* At least one unused cache entry. A simple |
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* round-robin strategy is used to choose the entry to |
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* be evicted from the cache. |
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*/ |
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i = cache->next_blk; |
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for (n = 0; n < cache->entries; n++) { |
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if (cache->entry[i].refcount == 0) |
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break; |
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i = (i + 1) % cache->entries; |
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} |
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cache->next_blk = (i + 1) % cache->entries; |
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entry = &cache->entry[i]; |
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/* |
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* Initialise chosen cache entry, and fill it in from |
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* disk. |
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*/ |
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cache->unused--; |
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entry->block = block; |
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entry->refcount = 1; |
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entry->pending = 1; |
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entry->num_waiters = 0; |
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entry->error = 0; |
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spin_unlock(&cache->lock); |
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entry->length = squashfs_read_data(sb, block, length, |
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&entry->next_index, entry->actor); |
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spin_lock(&cache->lock); |
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if (entry->length < 0) |
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entry->error = entry->length; |
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entry->pending = 0; |
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/* |
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* While filling this entry one or more other processes |
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* have looked it up in the cache, and have slept |
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* waiting for it to become available. |
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*/ |
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if (entry->num_waiters) { |
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spin_unlock(&cache->lock); |
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wake_up_all(&entry->wait_queue); |
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} else |
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spin_unlock(&cache->lock); |
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goto out; |
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} |
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/* |
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* Block already in cache. Increment refcount so it doesn't |
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* get reused until we're finished with it, if it was |
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* previously unused there's one less cache entry available |
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* for reuse. |
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*/ |
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entry = &cache->entry[i]; |
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if (entry->refcount == 0) |
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cache->unused--; |
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entry->refcount++; |
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/* |
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* If the entry is currently being filled in by another process |
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* go to sleep waiting for it to become available. |
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*/ |
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if (entry->pending) { |
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entry->num_waiters++; |
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spin_unlock(&cache->lock); |
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wait_event(entry->wait_queue, !entry->pending); |
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} else |
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spin_unlock(&cache->lock); |
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goto out; |
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} |
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out: |
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TRACE("Got %s %d, start block %lld, refcount %d, error %d\n", |
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cache->name, i, entry->block, entry->refcount, entry->error); |
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if (entry->error) |
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ERROR("Unable to read %s cache entry [%llx]\n", cache->name, |
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block); |
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return entry; |
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} |
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/* |
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* Release cache entry, once usage count is zero it can be reused. |
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*/ |
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void squashfs_cache_put(struct squashfs_cache_entry *entry) |
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{ |
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struct squashfs_cache *cache = entry->cache; |
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spin_lock(&cache->lock); |
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entry->refcount--; |
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if (entry->refcount == 0) { |
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cache->unused++; |
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/* |
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* If there's any processes waiting for a block to become |
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* available, wake one up. |
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*/ |
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if (cache->num_waiters) { |
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spin_unlock(&cache->lock); |
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wake_up(&cache->wait_queue); |
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return; |
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} |
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} |
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spin_unlock(&cache->lock); |
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} |
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/* |
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* Delete cache reclaiming all kmalloced buffers. |
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*/ |
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void squashfs_cache_delete(struct squashfs_cache *cache) |
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{ |
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int i, j; |
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if (cache == NULL) |
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return; |
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for (i = 0; i < cache->entries; i++) { |
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if (cache->entry[i].data) { |
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for (j = 0; j < cache->pages; j++) |
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kfree(cache->entry[i].data[j]); |
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kfree(cache->entry[i].data); |
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} |
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kfree(cache->entry[i].actor); |
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} |
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kfree(cache->entry); |
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kfree(cache); |
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} |
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/* |
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* Initialise cache allocating the specified number of entries, each of |
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* size block_size. To avoid vmalloc fragmentation issues each entry |
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* is allocated as a sequence of kmalloced PAGE_SIZE buffers. |
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*/ |
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struct squashfs_cache *squashfs_cache_init(char *name, int entries, |
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int block_size) |
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{ |
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int i, j; |
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struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL); |
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if (cache == NULL) { |
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ERROR("Failed to allocate %s cache\n", name); |
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return NULL; |
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} |
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cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL); |
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if (cache->entry == NULL) { |
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ERROR("Failed to allocate %s cache\n", name); |
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goto cleanup; |
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} |
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cache->curr_blk = 0; |
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cache->next_blk = 0; |
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cache->unused = entries; |
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cache->entries = entries; |
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cache->block_size = block_size; |
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cache->pages = block_size >> PAGE_SHIFT; |
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cache->pages = cache->pages ? cache->pages : 1; |
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cache->name = name; |
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cache->num_waiters = 0; |
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spin_lock_init(&cache->lock); |
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init_waitqueue_head(&cache->wait_queue); |
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for (i = 0; i < entries; i++) { |
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struct squashfs_cache_entry *entry = &cache->entry[i]; |
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init_waitqueue_head(&cache->entry[i].wait_queue); |
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entry->cache = cache; |
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entry->block = SQUASHFS_INVALID_BLK; |
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entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL); |
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if (entry->data == NULL) { |
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ERROR("Failed to allocate %s cache entry\n", name); |
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goto cleanup; |
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} |
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for (j = 0; j < cache->pages; j++) { |
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entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL); |
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if (entry->data[j] == NULL) { |
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ERROR("Failed to allocate %s buffer\n", name); |
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goto cleanup; |
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} |
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} |
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entry->actor = squashfs_page_actor_init(entry->data, |
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cache->pages, 0); |
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if (entry->actor == NULL) { |
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ERROR("Failed to allocate %s cache entry\n", name); |
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goto cleanup; |
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} |
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} |
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return cache; |
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cleanup: |
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squashfs_cache_delete(cache); |
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return NULL; |
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} |
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/* |
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* Copy up to length bytes from cache entry to buffer starting at offset bytes |
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* into the cache entry. If there's not length bytes then copy the number of |
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* bytes available. In all cases return the number of bytes copied. |
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*/ |
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int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry, |
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int offset, int length) |
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{ |
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int remaining = length; |
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if (length == 0) |
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return 0; |
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else if (buffer == NULL) |
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return min(length, entry->length - offset); |
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while (offset < entry->length) { |
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void *buff = entry->data[offset / PAGE_SIZE] |
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+ (offset % PAGE_SIZE); |
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int bytes = min_t(int, entry->length - offset, |
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PAGE_SIZE - (offset % PAGE_SIZE)); |
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if (bytes >= remaining) { |
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memcpy(buffer, buff, remaining); |
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remaining = 0; |
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break; |
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} |
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memcpy(buffer, buff, bytes); |
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buffer += bytes; |
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remaining -= bytes; |
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offset += bytes; |
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} |
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return length - remaining; |
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} |
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/* |
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* Read length bytes from metadata position <block, offset> (block is the |
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* start of the compressed block on disk, and offset is the offset into |
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* the block once decompressed). Data is packed into consecutive blocks, |
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* and length bytes may require reading more than one block. |
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*/ |
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int squashfs_read_metadata(struct super_block *sb, void *buffer, |
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u64 *block, int *offset, int length) |
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{ |
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struct squashfs_sb_info *msblk = sb->s_fs_info; |
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int bytes, res = length; |
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struct squashfs_cache_entry *entry; |
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TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset); |
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if (unlikely(length < 0)) |
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return -EIO; |
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while (length) { |
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entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0); |
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if (entry->error) { |
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res = entry->error; |
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goto error; |
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} else if (*offset >= entry->length) { |
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res = -EIO; |
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goto error; |
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} |
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bytes = squashfs_copy_data(buffer, entry, *offset, length); |
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if (buffer) |
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buffer += bytes; |
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length -= bytes; |
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*offset += bytes; |
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if (*offset == entry->length) { |
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*block = entry->next_index; |
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*offset = 0; |
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} |
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squashfs_cache_put(entry); |
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} |
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return res; |
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error: |
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squashfs_cache_put(entry); |
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return res; |
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} |
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/* |
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* Look-up in the fragmment cache the fragment located at <start_block> in the |
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* filesystem. If necessary read and decompress it from disk. |
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*/ |
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struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb, |
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u64 start_block, int length) |
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{ |
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struct squashfs_sb_info *msblk = sb->s_fs_info; |
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return squashfs_cache_get(sb, msblk->fragment_cache, start_block, |
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length); |
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} |
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/* |
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* Read and decompress the datablock located at <start_block> in the |
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* filesystem. The cache is used here to avoid duplicating locking and |
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* read/decompress code. |
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*/ |
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struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb, |
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u64 start_block, int length) |
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{ |
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struct squashfs_sb_info *msblk = sb->s_fs_info; |
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return squashfs_cache_get(sb, msblk->read_page, start_block, length); |
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} |
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/* |
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* Read a filesystem table (uncompressed sequence of bytes) from disk |
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*/ |
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void *squashfs_read_table(struct super_block *sb, u64 block, int length) |
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{ |
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int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT; |
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int i, res; |
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void *table, *buffer, **data; |
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struct squashfs_page_actor *actor; |
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table = buffer = kmalloc(length, GFP_KERNEL); |
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if (table == NULL) |
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return ERR_PTR(-ENOMEM); |
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data = kcalloc(pages, sizeof(void *), GFP_KERNEL); |
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if (data == NULL) { |
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res = -ENOMEM; |
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goto failed; |
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} |
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actor = squashfs_page_actor_init(data, pages, length); |
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if (actor == NULL) { |
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res = -ENOMEM; |
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goto failed2; |
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} |
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for (i = 0; i < pages; i++, buffer += PAGE_SIZE) |
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data[i] = buffer; |
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res = squashfs_read_data(sb, block, length | |
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SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor); |
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kfree(data); |
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kfree(actor); |
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if (res < 0) |
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goto failed; |
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return table; |
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failed2: |
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kfree(data); |
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failed: |
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kfree(table); |
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return ERR_PTR(res); |
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}
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