/* * Squashfs - a compressed read only filesystem for Linux * * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 * Phillip Lougher * * 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 #include #include #include #include #include #include #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 . */ 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 ca