Squashfs: regular file operations
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
This commit is contained in:
Phillip Lougher
Родитель
07972dde75
Коммит
1701aecb68
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@ -0,0 +1,502 @@
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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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* file.c
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*/
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/*
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* This file contains code for handling regular files. A regular file
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* consists of a sequence of contiguous compressed blocks, and/or a
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* compressed fragment block (tail-end packed block). The compressed size
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* of each datablock is stored in a block list contained within the
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* file inode (itself stored in one or more compressed metadata blocks).
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*
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* To speed up access to datablocks when reading 'large' files (256 Mbytes or
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* larger), the code implements an index cache that caches the mapping from
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* block index to datablock location on disk.
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*
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* The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
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* retaining a simple and space-efficient block list on disk. The cache
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* is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
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* Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
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* The index cache is designed to be memory efficient, and by default uses
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* 16 KiB.
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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/kernel.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/pagemap.h>
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#include <linux/mutex.h>
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#include <linux/zlib.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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* Locate cache slot in range [offset, index] for specified inode. If
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* there's more than one return the slot closest to index.
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*/
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static struct meta_index *locate_meta_index(struct inode *inode, int offset,
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int index)
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{
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struct meta_index *meta = NULL;
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struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
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int i;
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mutex_lock(&msblk->meta_index_mutex);
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TRACE("locate_meta_index: index %d, offset %d\n", index, offset);
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if (msblk->meta_index == NULL)
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goto not_allocated;
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for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
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if (msblk->meta_index[i].inode_number == inode->i_ino &&
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msblk->meta_index[i].offset >= offset &&
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msblk->meta_index[i].offset <= index &&
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msblk->meta_index[i].locked == 0) {
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TRACE("locate_meta_index: entry %d, offset %d\n", i,
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msblk->meta_index[i].offset);
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meta = &msblk->meta_index[i];
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offset = meta->offset;
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}
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}
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if (meta)
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meta->locked = 1;
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not_allocated:
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mutex_unlock(&msblk->meta_index_mutex);
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return meta;
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}
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/*
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* Find and initialise an empty cache slot for index offset.
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*/
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static struct meta_index *empty_meta_index(struct inode *inode, int offset,
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int skip)
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{
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struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
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struct meta_index *meta = NULL;
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int i;
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mutex_lock(&msblk->meta_index_mutex);
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TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);
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if (msblk->meta_index == NULL) {
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/*
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* First time cache index has been used, allocate and
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* initialise. The cache index could be allocated at
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* mount time but doing it here means it is allocated only
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* if a 'large' file is read.
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*/
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msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
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sizeof(*(msblk->meta_index)), GFP_KERNEL);
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if (msblk->meta_index == NULL) {
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ERROR("Failed to allocate meta_index\n");
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goto failed;
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}
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for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
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msblk->meta_index[i].inode_number = 0;
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msblk->meta_index[i].locked = 0;
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}
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msblk->next_meta_index = 0;
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}
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for (i = SQUASHFS_META_SLOTS; i &&
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msblk->meta_index[msblk->next_meta_index].locked; i--)
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msblk->next_meta_index = (msblk->next_meta_index + 1) %
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SQUASHFS_META_SLOTS;
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if (i == 0) {
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TRACE("empty_meta_index: failed!\n");
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goto failed;
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}
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TRACE("empty_meta_index: returned meta entry %d, %p\n",
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msblk->next_meta_index,
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&msblk->meta_index[msblk->next_meta_index]);
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meta = &msblk->meta_index[msblk->next_meta_index];
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msblk->next_meta_index = (msblk->next_meta_index + 1) %
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SQUASHFS_META_SLOTS;
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meta->inode_number = inode->i_ino;
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meta->offset = offset;
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meta->skip = skip;
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meta->entries = 0;
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meta->locked = 1;
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failed:
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mutex_unlock(&msblk->meta_index_mutex);
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return meta;
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}
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static void release_meta_index(struct inode *inode, struct meta_index *meta)
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{
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struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
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mutex_lock(&msblk->meta_index_mutex);
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meta->locked = 0;
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mutex_unlock(&msblk->meta_index_mutex);
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}
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/*
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* Read the next n blocks from the block list, starting from
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* metadata block <start_block, offset>.
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*/
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static long long read_indexes(struct super_block *sb, int n,
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u64 *start_block, int *offset)
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{
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int err, i;
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long long block = 0;
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__le32 *blist = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
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if (blist == NULL) {
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ERROR("read_indexes: Failed to allocate block_list\n");
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return -ENOMEM;
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}
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while (n) {
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int blocks = min_t(int, n, PAGE_CACHE_SIZE >> 2);
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err = squashfs_read_metadata(sb, blist, start_block,
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offset, blocks << 2);
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if (err < 0) {
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ERROR("read_indexes: reading block [%llx:%x]\n",
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*start_block, *offset);
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goto failure;
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}
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for (i = 0; i < blocks; i++) {
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int size = le32_to_cpu(blist[i]);
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block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
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}
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n -= blocks;
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}
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kfree(blist);
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return block;
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failure:
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kfree(blist);
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return err;
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}
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/*
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* Each cache index slot has SQUASHFS_META_ENTRIES, each of which
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* can cache one index -> datablock/blocklist-block mapping. We wish
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* to distribute these over the length of the file, entry[0] maps index x,
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* entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
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* The larger the file, the greater the skip factor. The skip factor is
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* limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
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* the number of metadata blocks that need to be read fits into the cache.
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* If the skip factor is limited in this way then the file will use multiple
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* slots.
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*/
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static inline int calculate_skip(int blocks)
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{
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int skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
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* SQUASHFS_META_INDEXES);
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return min(SQUASHFS_CACHED_BLKS - 1, skip + 1);
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}
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/*
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* Search and grow the index cache for the specified inode, returning the
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* on-disk locations of the datablock and block list metadata block
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* <index_block, index_offset> for index (scaled to nearest cache index).
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*/
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static int fill_meta_index(struct inode *inode, int index,
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u64 *index_block, int *index_offset, u64 *data_block)
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{
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struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
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int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
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int offset = 0;
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struct meta_index *meta;
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struct meta_entry *meta_entry;
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u64 cur_index_block = squashfs_i(inode)->block_list_start;
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int cur_offset = squashfs_i(inode)->offset;
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u64 cur_data_block = squashfs_i(inode)->start;
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int err, i;
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/*
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* Scale index to cache index (cache slot entry)
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*/
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index /= SQUASHFS_META_INDEXES * skip;
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while (offset < index) {
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meta = locate_meta_index(inode, offset + 1, index);
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if (meta == NULL) {
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meta = empty_meta_index(inode, offset + 1, skip);
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if (meta == NULL)
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goto all_done;
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} else {
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offset = index < meta->offset + meta->entries ? index :
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meta->offset + meta->entries - 1;
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meta_entry = &meta->meta_entry[offset - meta->offset];
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cur_index_block = meta_entry->index_block +
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msblk->inode_table;
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cur_offset = meta_entry->offset;
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cur_data_block = meta_entry->data_block;
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TRACE("get_meta_index: offset %d, meta->offset %d, "
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"meta->entries %d\n", offset, meta->offset,
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meta->entries);
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TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
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" data_block 0x%llx\n", cur_index_block,
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cur_offset, cur_data_block);
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}
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/*
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* If necessary grow cache slot by reading block list. Cache
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* slot is extended up to index or to the end of the slot, in
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* which case further slots will be used.
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*/
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for (i = meta->offset + meta->entries; i <= index &&
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i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
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int blocks = skip * SQUASHFS_META_INDEXES;
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long long res = read_indexes(inode->i_sb, blocks,
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&cur_index_block, &cur_offset);
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if (res < 0) {
|
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if (meta->entries == 0)
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/*
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* Don't leave an empty slot on read
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* error allocated to this inode...
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*/
|
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meta->inode_number = 0;
|
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err = res;
|
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goto failed;
|
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}
|
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|
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cur_data_block += res;
|
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meta_entry = &meta->meta_entry[i - meta->offset];
|
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meta_entry->index_block = cur_index_block -
|
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msblk->inode_table;
|
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meta_entry->offset = cur_offset;
|
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meta_entry->data_block = cur_data_block;
|
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meta->entries++;
|
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offset++;
|
||||
}
|
||||
|
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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);
|
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return err;
|
||||
}
|
||||
|
||||
|
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/*
|
||||
* 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
|
||||
};
|
||||
Загрузка…
Ссылка в новой задаче