// 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 <phillip@squashfs.org.uk>
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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 "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_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_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 = squashfs_block_size(blist[i]);
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if (size < 0) {
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err = size;
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goto failure;
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}
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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(u64 blocks)
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{
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u64 skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
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* SQUASHFS_META_INDEXES);
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return min((u64) 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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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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}
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TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
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meta->offset, meta->entries);
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release_meta_index(inode, meta);
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}
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all_done:
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*index_block = cur_index_block;
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*index_offset = cur_offset;
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*data_block = cur_data_block;
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/*
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* Scale cache index (cache slot entry) to index
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*/
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return offset * SQUASHFS_META_INDEXES * skip;
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failed:
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release_meta_index(inode, meta);
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return err;
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}
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/*
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* Get the on-disk location and compressed size of the datablock
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* specified by index. Fill_meta_index() does most of the work.
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*/
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static int read_blocklist(struct inode *inode, int index, u64 *block)
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{
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u64 start;
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long long blks;
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int offset;
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__le32 size;
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int res = fill_meta_index(inode, index, &start, &offset, block);
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TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
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" 0x%x, block 0x%llx\n", res, index, start, offset,
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*block);
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if (res < 0)
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return res;
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/*
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* res contains the index of the mapping returned by fill_meta_index(),
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* this will likely be less than the desired index (because the
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* meta_index cache works at a higher granularity). Read any
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* extra block indexes needed.
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*/
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if (res < index) {
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blks = read_indexes(inode->i_sb, index - res, &start, &offset);
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if (blks < 0)
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return (int) blks;
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*block += blks;
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}
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/*
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* Read length of block specified by index.
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*/
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res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
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sizeof(size));
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if (res < 0)
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return res;
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return squashfs_block_size(size);
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}
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void squashfs_fill_page(struct page *page, struct squashfs_cache_entry *buffer, int offset, int avail)
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{
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int copied;
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void *pageaddr;
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pageaddr = kmap_atomic(page);
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copied = squashfs_copy_data(pageaddr, buffer, offset, avail);
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memset(pageaddr + copied, 0, PAGE_SIZE - copied);
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kunmap_atomic(pageaddr);
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flush_dcache_page(page);
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if (copied == avail)
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SetPageUptodate(page);
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else
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SetPageError(page);
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}
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/* Copy data into page cache */
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void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer,
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int bytes, int offset)
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{
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struct inode *inode = page->mapping->host;
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struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
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int i, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
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int start_index = page->index & ~mask, end_index = start_index | mask;
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/*
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* Loop copying datablock into pages. As the datablock likely covers
|
* many PAGE_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.
|
*/
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for (i = start_index; i <= end_index && bytes > 0; i++,
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bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
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struct page *push_page;
|
int avail = buffer ? min_t(int, bytes, PAGE_SIZE) : 0;
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|
TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);
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|
push_page = (i == page->index) ? page :
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grab_cache_page_nowait(page->mapping, i);
|
|
if (!push_page)
|
continue;
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|
if (PageUptodate(push_page))
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goto skip_page;
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squashfs_fill_page(push_page, buffer, offset, avail);
|
skip_page:
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unlock_page(push_page);
|
if (i != page->index)
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put_page(push_page);
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}
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}
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/* Read datablock stored packed inside a fragment (tail-end packed block) */
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static int squashfs_readpage_fragment(struct page *page, int expected)
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{
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struct inode *inode = page->mapping->host;
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struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
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squashfs_i(inode)->fragment_block,
|
squashfs_i(inode)->fragment_size);
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int res = buffer->error;
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|
if (res)
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ERROR("Unable to read page, block %llx, size %x\n",
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squashfs_i(inode)->fragment_block,
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squashfs_i(inode)->fragment_size);
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else
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squashfs_copy_cache(page, buffer, expected,
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squashfs_i(inode)->fragment_offset);
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squashfs_cache_put(buffer);
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return res;
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}
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static int squashfs_readpage_sparse(struct page *page, int expected)
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{
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squashfs_copy_cache(page, NULL, expected, 0);
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return 0;
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}
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static int squashfs_readpage(struct file *file, struct page *page)
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{
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struct inode *inode = page->mapping->host;
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struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
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int index = page->index >> (msblk->block_log - PAGE_SHIFT);
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int file_end = i_size_read(inode) >> msblk->block_log;
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int expected = index == file_end ?
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(i_size_read(inode) & (msblk->block_size - 1)) :
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msblk->block_size;
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int res;
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void *pageaddr;
|
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TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
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page->index, squashfs_i(inode)->start);
|
|
if (page->index >= ((i_size_read(inode) + PAGE_SIZE - 1) >>
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PAGE_SHIFT))
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goto out;
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if (index < file_end || squashfs_i(inode)->fragment_block ==
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SQUASHFS_INVALID_BLK) {
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u64 block = 0;
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int bsize = read_blocklist(inode, index, &block);
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if (bsize < 0)
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goto error_out;
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if (bsize == 0)
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res = squashfs_readpage_sparse(page, expected);
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else
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res = squashfs_readpage_block(page, block, bsize, expected);
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} else
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res = squashfs_readpage_fragment(page, expected);
|
|
if (!res)
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return 0;
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|
error_out:
|
SetPageError(page);
|
out:
|
pageaddr = kmap_atomic(page);
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memset(pageaddr, 0, PAGE_SIZE);
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kunmap_atomic(pageaddr);
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flush_dcache_page(page);
|
if (!PageError(page))
|
SetPageUptodate(page);
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unlock_page(page);
|
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return 0;
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}
|
|
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const struct address_space_operations squashfs_aops = {
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.readpage = squashfs_readpage
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};
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