1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Squashfs - a compressed read only filesystem for Linux
5 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
6 * Phillip Lougher <phillip@squashfs.org.uk>
12 * This file implements the low-level routines to read and decompress
13 * datablocks and metadata blocks.
17 #include <linux/vfs.h>
18 #include <linux/slab.h>
19 #include <linux/string.h>
20 #include <linux/buffer_head.h>
21 #include <linux/bio.h>
23 #include "squashfs_fs.h"
24 #include "squashfs_fs_sb.h"
26 #include "decompressor.h"
27 #include "page_actor.h"
30 * Read the metadata block length, this is stored in the first two
31 * bytes of the metadata block.
33 static struct buffer_head *get_block_length(struct super_block *sb,
34 u64 *cur_index, int *offset, int *length)
36 struct squashfs_sb_info *msblk = sb->s_fs_info;
37 struct buffer_head *bh;
39 bh = sb_bread(sb, *cur_index);
43 if (msblk->devblksize - *offset == 1) {
44 *length = (unsigned char) bh->b_data[*offset];
46 bh = sb_bread(sb, ++(*cur_index));
49 *length |= (unsigned char) bh->b_data[0] << 8;
52 *length = (unsigned char) bh->b_data[*offset] |
53 (unsigned char) bh->b_data[*offset + 1] << 8;
56 if (*offset == msblk->devblksize) {
58 bh = sb_bread(sb, ++(*cur_index));
70 * Read and decompress a metadata block or datablock. Length is non-zero
71 * if a datablock is being read (the size is stored elsewhere in the
72 * filesystem), otherwise the length is obtained from the first two bytes of
73 * the metadata block. A bit in the length field indicates if the block
74 * is stored uncompressed in the filesystem (usually because compression
75 * generated a larger block - this does occasionally happen with compression
78 int squashfs_read_data(struct super_block *sb, u64 index, int length,
79 u64 *next_index, struct squashfs_page_actor *output)
81 struct squashfs_sb_info *msblk = sb->s_fs_info;
82 struct buffer_head **bh;
83 int offset = index & ((1 << msblk->devblksize_log2) - 1);
84 u64 cur_index = index >> msblk->devblksize_log2;
85 int bytes, compressed, b = 0, k = 0, avail, i;
87 bh = kcalloc(((output->length + msblk->devblksize - 1)
88 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
97 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
98 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
100 *next_index = index + length;
102 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
103 index, compressed ? "" : "un", length, output->length);
105 if (length < 0 || length > output->length ||
106 (index + length) > msblk->bytes_used)
109 for (b = 0; bytes < length; b++, cur_index++) {
110 bh[b] = sb_getblk(sb, cur_index);
113 bytes += msblk->devblksize;
115 ll_rw_block(REQ_OP_READ, 0, b, bh);
120 if ((index + 2) > msblk->bytes_used)
123 bh[0] = get_block_length(sb, &cur_index, &offset, &length);
128 bytes = msblk->devblksize - offset;
129 compressed = SQUASHFS_COMPRESSED(length);
130 length = SQUASHFS_COMPRESSED_SIZE(length);
132 *next_index = index + length + 2;
134 TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
135 compressed ? "" : "un", length);
137 if (length < 0 || length > output->length ||
138 (index + length) > msblk->bytes_used)
141 for (; bytes < length; b++) {
142 bh[b] = sb_getblk(sb, ++cur_index);
145 bytes += msblk->devblksize;
147 ll_rw_block(REQ_OP_READ, 0, b - 1, bh + 1);
150 for (i = 0; i < b; i++) {
151 wait_on_buffer(bh[i]);
152 if (!buffer_uptodate(bh[i]))
159 length = squashfs_decompress(msblk, bh, b, offset, length,
165 * Block is uncompressed.
167 int in, pg_offset = 0;
168 void *data = squashfs_first_page(output);
170 for (bytes = length; k < b; k++) {
171 in = min(bytes, msblk->devblksize - offset);
174 if (pg_offset == PAGE_SIZE) {
175 data = squashfs_next_page(output);
178 avail = min_t(int, in, PAGE_SIZE -
180 memcpy(data + pg_offset, bh[k]->b_data + offset,
189 squashfs_finish_page(output);
200 ERROR("squashfs_read_data failed to read block 0x%llx\n",
201 (unsigned long long) index);