// SPDX-License-Identifier: GPL-2.0-or-later /* * Squashfs - a compressed read only filesystem for Linux * * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 * Phillip Lougher <phillip@squashfs.org.uk> * * 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_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_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 = squashfs_block_size(blist[i]); if (size < 0) { err = size; goto failure; } 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 squashfs_block_size(size); } void squashfs_fill_page(struct page *page, struct squashfs_cache_entry *buffer, int offset, int avail) { int copied; void *pageaddr; pageaddr = kmap_atomic(page); copied = squashfs_copy_data(pageaddr, buffer, offset, avail); memset(pageaddr + copied, 0, PAGE_SIZE - copied); kunmap_atomic(pageaddr); flush_dcache_page(page); if (copied == avail) SetPageUptodate(page); else SetPageError(page); } /* Copy data into page cache */ void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer, int bytes, int offset) { struct inode *inode = page->mapping->host; struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info; int i, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1; int start_index = page->index & ~mask, end_index = start_index | mask; /* * 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. */ for (i = start_index; i <= end_index && bytes > 0; i++, bytes -= PAGE_SIZE, offset += PAGE_SIZE) { struct page *push_page; int avail = buffer ? min_t(int, bytes, PAGE_SIZE) : 0; 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; squashfs_fill_page(push_page, buffer, offset, avail); skip_page: unlock_page(push_page); if (i != page->index) put_page(push_page); } } /* Read datablock stored packed inside a fragment (tail-end packed block) */ static int squashfs_readpage_fragment(struct page *page, int expected) { struct inode *inode = page->mapping->host; struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb, squashfs_i(inode)->fragment_block, squashfs_i(inode)->fragment_size); int res = buffer->error; if (res) ERROR("Unable to read page, block %llx, size %x\n", squashfs_i(inode)->fragment_block, squashfs_i(inode)->fragment_size); else squashfs_copy_cache(page, buffer, expected, squashfs_i(inode)->fragment_offset); squashfs_cache_put(buffer); return res; } static int squashfs_readpage_sparse(struct page *page, int expected) { squashfs_copy_cache(page, NULL, expected, 0); return 0; } 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 index = page->index >> (msblk->block_log - PAGE_SHIFT); int file_end = i_size_read(inode) >> msblk->block_log; int expected = index == file_end ? (i_size_read(inode) & (msblk->block_size - 1)) : msblk->block_size; int res; void *pageaddr; 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_SIZE - 1) >> PAGE_SHIFT)) goto out; if (index < file_end || squashfs_i(inode)->fragment_block == SQUASHFS_INVALID_BLK) { u64 block = 0; int bsize = read_blocklist(inode, index, &block); if (bsize < 0) goto error_out; if (bsize == 0) res = squashfs_readpage_sparse(page, expected); else res = squashfs_readpage_block(page, block, bsize, expected); } else res = squashfs_readpage_fragment(page, expected); if (!res) return 0; error_out: SetPageError(page); out: pageaddr = kmap_atomic(page); memset(pageaddr, 0, PAGE_SIZE); kunmap_atomic(pageaddr); flush_dcache_page(page); if (!PageError(page)) SetPageUptodate(page); unlock_page(page); return 0; } const struct address_space_operations squashfs_aops = { .readpage = squashfs_readpage };