- 根目录:
- fs
- squashfs
- file.c
/*
* 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.
*
* file.c
*/
/*
* This file contains code for handling regular files. A regular file
* consists of a sequence of contiguous compressed blocks, and/or a
* compressed fragment block (tail-end packed block). The compressed size
* of each datablock is stored in a block list contained within the
* file inode (itself stored in one or more compressed metadata blocks).
*
* To speed up access to datablocks when reading 'large' files (256 Mbytes or
* larger), the code implements an index cache that caches the mapping from
* block index to datablock location on disk.
*
* The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
* retaining a simple and space-efficient block list on disk. The cache
* is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
* Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
* The index cache is designed to be memory efficient, and by default uses
* 16 KiB.
*/
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/pagemap.h>
#include <linux/mutex.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
/*
* Locate cache slot in range [offset, index] for specified inode. If
* there's more than one return the slot closest to index.
*/
static struct meta_index *locate_meta_index(struct inode *inode, int offset,
int index)
{
struct meta_index *meta = NULL;
struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
int i;
mutex_lock(&msblk->meta_index_mutex);
TRACE("locate_meta_index: index %d, offset %d\n", index, offset);
if (msblk->meta_index == NULL)
goto not_allocated;
for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
if (msblk->meta_index[i].inode_number == inode->i_ino &&
msblk->meta_index[i].offset >= offset &&
msblk->meta_index[i].offset <= index &&
msblk->meta_index[i].locked == 0) {
TRACE("locate_meta_index: entry %d, offset %d\n", i,
msblk->meta_index[i].offset);
meta = &msblk->meta_index[i];
offset = meta->offset;
}
}
if (meta)
meta->locked = 1;
not_allocated:
mutex_unlock(&msblk->meta_index_mutex);
return meta;
}
/*
* Find and initialise an empty cache slot for index offset.
*/
static struct meta_index *empty_meta_index(struct inode *inode, int offset,
int skip)
{
struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
struct meta_index *meta = NULL;
int i;
mutex_lock(&msblk->meta_index_mutex);
TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);
if (msblk->meta_index == NULL) {
/*
* First time cache index has been used, allocate and
* initialise. The cache index could be allocated at
* mount time but doing it here means it is allocated only
* if a 'large' file is read.
*/
msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
sizeof(*(msblk->meta_index)), GFP_KERNEL);
if (msblk->meta_index == NULL) {
ERROR("Failed to allocate meta_index\n");
goto failed;
}
for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
msblk->meta_index[i].inode_number = 0;
msblk->meta_index[i].locked = 0;
}
msblk->next_meta_index = 0;
}
for (i = SQUASHFS_META_SLOTS; i &&
msblk->meta_index[msblk->next_meta_index].locked; i--)
msblk->next_meta_index = (msblk->next_meta_index + 1) %
SQUASHFS_META_SLOTS;
if (i == 0) {
TRACE("empty_meta_index: failed!\n");
goto failed;
}
TRACE("empty_meta_index: returned meta entry %d, %p\n",
msblk->next_meta_index,
&msblk->meta_index[msblk->next_meta_index]);
meta = &msblk->meta_index[msblk->next_meta_index];
msblk->next_meta_index = (msblk->next_meta_index + 1) %
SQUASHFS_META_SLOTS;
meta->inode_number = inode->i_ino;
meta->offset = offset;
meta->skip = skip;
meta->entries = 0;
meta->locked = 1;
failed:
mutex_unlock(&msblk->meta_index_mutex);
return meta;
}
static void release_meta_index(struct inode *inode, struct meta_index *meta)
{
struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
mutex_lock(&msblk->meta_index_mutex);
meta->locked = 0;
mutex_unlock(&msblk->meta_index_mutex);
}
/*
* Read the next n blocks from the block list, starting from
* metadata block <start_block, offset>.
*/
static long long read_indexes(struct super_block *sb, int n,
u64 *start_block, int *offset)
{
int err, i;
long long block = 0;
__le32 *blist = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
if (blist == NULL) {
ERROR("read_indexes: Failed to allocate block_list\n");
return -ENOMEM;
}
while (n) {
int blocks = min_t(int, n, PAGE_CACHE_SIZE >> 2);
err = squashfs_read_metadata(sb, blist, start_block,
offset, blocks << 2);
if (err < 0) {
ERROR("read_indexes: reading block [%llx:%x]\n",
*start_block, *offset);
goto failure;
}
for (i = 0; i < blocks; i++) {
int size = le32_to_cpu(blist[i]);
block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
}
n -= blocks;
}
kfree(blist);
return block;
failure:
kfree(blist);
return err;
}
/*
* Each cache index slot has SQUASHFS_META_ENTRIES, each of which
* can cache one index -> datablock/blocklist-block mapping. We wish
* to distribute these over the length of the file, entry[0] maps index x,
* entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
* The larger the file, the greater the skip factor. The skip factor is
* limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
* the number of metadata blocks that need to be read fits into the cache.
* If the skip factor is limited in this way then the file will use multiple
* slots.
*/
static inline int calculate_skip(int blocks)
{
int skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
* SQUASHFS_META_INDEXES);
return min(SQUASHFS_CACHED_BLKS - 1, skip + 1);
}
/*
* Search and grow the index cache for the specified inode, returning the
* on-disk locations of the datablock and block list metadata block
* <index_block, index_offset> for index (scaled to nearest cache index).
*/
static int fill_meta_index(struct inode *inode, int index,
u64 *index_block, int *index_offset, u64 *data_block)
{
struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
int offset = 0;
struct meta_index *meta;
struct meta_entry *meta_entry;
u64 cur_index_block = squashfs_i(inode)->block_list_start;
int cur_offset = squashfs_i(inode)->offset;
u64 cur_data_block = squashfs_i(inode)->start;
int err, i;
/*
* Scale index to cache index (cache slot entry)
*/
index /= SQUASHFS_META_INDEXES * skip;
while (offset < index) {
meta = locate_meta_index(inode, offset + 1, index);
if (meta == NULL) {
meta = empty_meta_index(inode, offset + 1, skip);
if (meta == NULL)
goto all_done;
} else {
offset = index < meta->offset + meta->entries ? index :
meta->offset + meta->entries - 1;
meta_entry = &meta->meta_entry[offset - meta->offset];
cur_index_block = meta_entry->index_block +
msblk->inode_table;
cur_offset = meta_entry->offset;
cur_data_block = meta_entry->data_block;
TRACE("get_meta_index: offset %d, meta->offset %d, "
"meta->entries %d\n", offset, meta->offset,
meta->entries);
TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
" data_block 0x%llx\n", cur_index_block,
cur_offset, cur_data_block);
}
/*
* If necessary grow cache slot by reading block list. Cache
* slot is extended up to index or to the end of the slot, in
* which case further slots will be used.
*/
for (i = meta->offset + meta->entries; i <= index &&
i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
int blocks = skip * SQUASHFS_META_INDEXES;
long long res = read_indexes(inode->i_sb, blocks,
&cur_index_block, &cur_offset);
if (res < 0) {
if (meta->entries == 0)
/*
* Don't leave an empty slot on read
* error allocated to this inode...
*/
meta->inode_number = 0;
err = res;
goto failed;
}
cur_data_block += res;
meta_entry = &meta->meta_entry[i - meta->offset];
meta_entry->index_block = cur_index_block -
msblk->inode_table;
meta_entry->offset = cur_offset;
meta_entry->data_block = cur_data_block;
meta->entries++;
offset++;
}
TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
meta->offset, meta->entries);
release_meta_index(inode, meta);
}
all_done:
*index_block = cur_index_block;
*index_offset = cur_offset;
*data_block = cur_data_block;
/*
* Scale cache index (cache slot entry) to index
*/
return offset * SQUASHFS_META_INDEXES * skip;
failed:
release_meta_index(inode, meta);
return err;
}
/*
* Get the on-disk location and compressed size of the datablock
* specified by index. Fill_meta_index() does most of the work.
*/
static int read_blocklist(struct inode *inode, int index, u64 *block)
{
u64 start;
long long blks;
int offset;
__le32 size;
int res = fill_meta_index(inode, index, &start, &offset, block);
TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
" 0x%x, block 0x%llx\n", res, index, start, offset,
*block);
if (res < 0)
return res;
/*
* res contains the index of the mapping returned by fill_meta_index(),
* this will likely be less than the desired index (because the
* meta_index cache works at a higher granularity). Read any
* extra block indexes needed.
*/
if (res < index) {
blks = read_indexes(inode->i_sb, index - res, &start, &offset);
if (blks < 0)
return (int) blks;
*block += blks;
}
/*
* Read length of block specified by index.
*/
res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
sizeof(size));
if (res < 0)
return res;
return le32_to_cpu(size);
}
static int squashfs_readpage(struct file *file, struct page *page)
{
struct inode *inode = page->mapping->host;
struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
int bytes, i, offset = 0, sparse = 0;
struct squashfs_cache_entry *buffer = NULL;
void *pageaddr;
int mask = (1 << (msblk->block_log - PAGE_CACHE_SHIFT)) - 1;
int index = page->index >> (msblk->block_log - PAGE_CACHE_SHIFT);
int start_index = page->index & ~mask;
int end_index = start_index | mask;
int file_end = i_size_read(inode) >> msblk->block_log;
TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
page->index, squashfs_i(inode)->start);
if (page->index >= ((i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
PAGE_CACHE_SHIFT))
goto out;
if (index < file_end || squashfs_i(inode)->fragment_block ==
SQUASHFS_INVALID_BLK) {
/*
* Reading a datablock from disk. Need to read block list
* to get location and block size.
*/
u64 block = 0;
int bsize = read_blocklist(inode, index, &block);
if (bsize < 0)
goto error_out;
if (bsize == 0) { /* hole */
bytes = index == file_end ?
(i_size_read(inode) & (msblk->block_size - 1)) :
msblk->block_size;
sparse = 1;
} else {
/*
* Read and decompress datablock.
*/
buffer = squashfs_get_datablock(inode->i_sb,
block, bsize);
if (buffer->error) {
ERROR("Unable to read page, block %llx, size %x"
"\n", block, bsize);
squashfs_cache_put(buffer);
goto error_out;
}
bytes = buffer->length;
}
} else {
/*
* Datablock is stored inside a fragment (tail-end packed
* block).
*/
buffer = squashfs_get_fragment(inode->i_sb,
squashfs_i(inode)->fragment_block,
squashfs_i(inode)->fragment_size);
if (buffer->error) {
ERROR("Unable to read page, block %llx, size %x\n",
squashfs_i(inode)->fragment_block,
squashfs_i(inode)->fragment_size);
squashfs_cache_put(buffer);
goto error_out;
}
bytes = i_size_read(inode) & (msblk->block_size - 1);
offset = squashfs_i(inode)->fragment_offset;
}
/*
* Loop copying datablock into pages. As the datablock likely covers
* many PAGE_CACHE_SIZE pages (default block size is 128 KiB) explicitly
* grab the pages from the page cache, except for the page that we've
* been called to fill.
*/
for (i = start_index; i <= end_index && bytes > 0; i++,
bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
struct page *push_page;
int avail = sparse ? 0 : min_t(int, bytes, PAGE_CACHE_SIZE);
TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);
push_page = (i == page->index) ? page :
grab_cache_page_nowait(page->mapping, i);
if (!push_page)
continue;
if (PageUptodate(push_page))
goto skip_page;
pageaddr = kmap_atomic(push_page, KM_USER0);
squashfs_copy_data(pageaddr, buffer, offset, avail);
memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
kunmap_atomic(pageaddr, KM_USER0);
flush_dcache_page(push_page);
SetPageUptodate(push_page);
skip_page:
unlock_page(push_page);
if (i != page->index)
page_cache_release(push_page);
}
if (!sparse)
squashfs_cache_put(buffer);
return 0;
error_out:
SetPageError(page);
out:
pageaddr = kmap_atomic(page, KM_USER0);
memset(pageaddr, 0, PAGE_CACHE_SIZE);
kunmap_atomic(pageaddr, KM_USER0);
flush_dcache_page(page);
if (!PageError(page))
SetPageUptodate(page);
unlock_page(page);
return 0;
}
const struct address_space_operations squashfs_aops = {
.readpage = squashfs_readpage
};