Squashfs: cache operations
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
This commit is contained in:
Phillip Lougher
Родитель
8256c8f631
Коммит
f400e12656
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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 <phillip@lougher.demon.co.uk>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2,
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* or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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* cache.c
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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 isssues with vmalloc the cache
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* uses sequences of kmalloced PAGE_CACHE_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/zlib.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_fs_i.h"
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#include "squashfs.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 = 0; i < cache->entries; i++)
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if (cache->entry[i].block == block)
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break;
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if (i == 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 choosen 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, entry->data,
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block, length, &entry->next_index,
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cache->block_size);
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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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}
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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_CACHE_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->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_CACHE_SHIFT;
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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_CACHE_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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}
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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 upto 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_CACHE_SIZE]
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+ (offset % PAGE_CACHE_SIZE);
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int bytes = min_t(int, entry->length - offset,
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PAGE_CACHE_SIZE - (offset % PAGE_CACHE_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, copied = 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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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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return entry->error;
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else if (*offset >= entry->length)
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return -EIO;
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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 copied;
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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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int squashfs_read_table(struct super_block *sb, void *buffer, u64 block,
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int length)
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{
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int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
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int i, res;
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void **data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
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if (data == NULL)
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return -ENOMEM;
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for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
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data[i] = buffer;
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res = squashfs_read_data(sb, data, block, length |
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SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length);
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kfree(data);
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return res;
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}
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