/*
* 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"
/*
* 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 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, entry->data,
block, length, &entry->next_index,
cache->block_size, cache->pages);
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->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;
}
}
}
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, 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
*/
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;
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;
}
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, pages);
kfree(data);
if (res < 0)
goto failed;
return table;
failed:
kfree(table);
return ERR_PTR(res);
}
