source: src/linux/universal/linux-4.9/fs/squashfs/block.c @ 31630

Last change on this file since 31630 was 31630, checked in by brainslayer, 4 months ago

new fs is compatible with standard squashfs, just smaller

File size: 5.5 KB
Line 
1/*
2 * Squashfs - a compressed read only filesystem for Linux
3 *
4 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
5 * Phillip Lougher <phillip@squashfs.org.uk>
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version 2,
10 * or (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20 *
21 * block.c
22 */
23
24/*
25 * This file implements the low-level routines to read and decompress
26 * datablocks and metadata blocks.
27 */
28
29#include <linux/fs.h>
30#include <linux/vfs.h>
31#include <linux/slab.h>
32#include <linux/string.h>
33#include <linux/buffer_head.h>
34
35#include "squashfs_fs.h"
36#include "squashfs_fs_sb.h"
37#include "squashfs.h"
38#include "decompressor.h"
39#include "page_actor.h"
40
41/*
42 * Read the metadata block length, this is stored in the first two
43 * bytes of the metadata block.
44 */
45static struct buffer_head *get_block_length(struct super_block *sb,
46                        u64 *cur_index, int *offset, int *length)
47{
48        struct squashfs_sb_info *msblk = sb->s_fs_info;
49        struct buffer_head *bh;
50
51        bh = sb_bread(sb, *cur_index);
52        if (bh == NULL)
53                return NULL;
54
55        if (msblk->devblksize - *offset == 1) {
56                *length = (unsigned char) bh->b_data[*offset];
57                put_bh(bh);
58                bh = sb_bread(sb, ++(*cur_index));
59                if (bh == NULL)
60                        return NULL;
61                *length |= (unsigned char) bh->b_data[0] << 8;
62                *offset = 1;
63        } else {
64                *length = (unsigned char) bh->b_data[*offset] |
65                        (unsigned char) bh->b_data[*offset + 1] << 8;
66                *offset += 2;
67
68                if (*offset == msblk->devblksize) {
69                        put_bh(bh);
70                        bh = sb_bread(sb, ++(*cur_index));
71                        if (bh == NULL)
72                                return NULL;
73                        *offset = 0;
74                }
75        }
76
77        return bh;
78}
79
80
81/*
82 * Read and decompress a metadata block or datablock.  Length is non-zero
83 * if a datablock is being read (the size is stored elsewhere in the
84 * filesystem), otherwise the length is obtained from the first two bytes of
85 * the metadata block.  A bit in the length field indicates if the block
86 * is stored uncompressed in the filesystem (usually because compression
87 * generated a larger block - this does occasionally happen with compression
88 * algorithms).
89 */
90int squashfs_read_data(struct super_block *sb, u64 index, int length,
91                u64 *next_index, struct squashfs_page_actor *output)
92{
93        struct squashfs_sb_info *msblk = sb->s_fs_info;
94        struct buffer_head **bh;
95        int offset = index & ((1 << msblk->devblksize_log2) - 1);
96        u64 cur_index = index >> msblk->devblksize_log2;
97        int bytes, compressed, b = 0, k = 0, avail, i;
98
99        bh = kcalloc(((output->length + msblk->devblksize - 1)
100                >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
101        if (bh == NULL)
102                return -ENOMEM;
103
104        if (length) {
105                /*
106                 * Datablock.
107                 */
108                bytes = -offset;
109                compressed = SQUASHFS_COMPRESSED_BLOCK(length);
110                length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
111                if (next_index)
112                        *next_index = index + length;
113
114                TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
115                        index, compressed ? "" : "un", length, output->length);
116
117                if (length < 0 || length > output->length ||
118                                (index + length) > msblk->bytes_used)
119                        goto read_failure;
120
121                for (b = 0; bytes < length; b++, cur_index++) {
122                        bh[b] = sb_getblk(sb, cur_index);
123                        if (bh[b] == NULL)
124                                goto block_release;
125                        bytes += msblk->devblksize;
126                }
127                ll_rw_block(REQ_OP_READ, 0, b, bh);
128        } else {
129                /*
130                 * Metadata block.
131                 */
132                if ((index + 2) > msblk->bytes_used)
133                        goto read_failure;
134
135                bh[0] = get_block_length(sb, &cur_index, &offset, &length);
136                if (bh[0] == NULL)
137                        goto read_failure;
138                b = 1;
139
140                bytes = msblk->devblksize - offset;
141                compressed = SQUASHFS_COMPRESSED(length);
142                length = SQUASHFS_COMPRESSED_SIZE(length);
143                if (next_index)
144                        *next_index = index + length + 2;
145
146                TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
147                                compressed ? "" : "un", length);
148
149                if (length < 0 || length > output->length ||
150                                        (index + length) > msblk->bytes_used)
151                        goto block_release;
152
153                for (; bytes < length; b++) {
154                        bh[b] = sb_getblk(sb, ++cur_index);
155                        if (bh[b] == NULL)
156                                goto block_release;
157                        bytes += msblk->devblksize;
158                }
159                ll_rw_block(REQ_OP_READ, 0, b - 1, bh + 1);
160        }
161
162        for (i = 0; i < b; i++) {
163                wait_on_buffer(bh[i]);
164                if (!buffer_uptodate(bh[i]))
165                        goto block_release;
166        }
167
168        if (compressed) {
169                length = squashfs_decompress(msblk, bh, b, offset, length,
170                        output);
171                if (length < 0)
172                        goto read_failure;
173        } else {
174                /*
175                 * Block is uncompressed.
176                 */
177                int in, pg_offset = 0;
178                void *data = squashfs_first_page(output);
179
180                for (bytes = length; k < b; k++) {
181                        in = min(bytes, msblk->devblksize - offset);
182                        bytes -= in;
183                        while (in) {
184                                if (pg_offset == PAGE_SIZE) {
185                                        data = squashfs_next_page(output);
186                                        pg_offset = 0;
187                                }
188                                avail = min_t(int, in, PAGE_SIZE -
189                                                pg_offset);
190                                memcpy(data + pg_offset, bh[k]->b_data + offset,
191                                                avail);
192                                in -= avail;
193                                pg_offset += avail;
194                                offset += avail;
195                        }
196                        offset = 0;
197                        put_bh(bh[k]);
198                }
199                squashfs_finish_page(output);
200        }
201
202        kfree(bh);
203        return length;
204
205block_release:
206        for (; k < b; k++)
207                put_bh(bh[k]);
208
209read_failure:
210        ERROR("squashfs_read_data failed to read block 0x%llx\n",
211                                        (unsigned long long) index);
212        kfree(bh);
213        return -EIO;
214}
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