fs/squashfs/block.c

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This source file includes following definitions.
get_block_length
squashfs_read_data
   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Squashfs - a compressed read only filesystem for Linux
   4  *
   5  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   6  * Phillip Lougher <phillip@squashfs.org.uk>
   7  *
   8  * block.c
   9  */
  10 
  11 /*
  12  * This file implements the low-level routines to read and decompress
  13  * datablocks and metadata blocks.
  14  */
  15 
  16 #include <linux/fs.h>
  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>
  22 
  23 #include "squashfs_fs.h"
  24 #include "squashfs_fs_sb.h"
  25 #include "squashfs.h"
  26 #include "decompressor.h"
  27 #include "page_actor.h"
  28 
  29 /*
  30  * Read the metadata block length, this is stored in the first two
  31  * bytes of the metadata block.
  32  */
  33 static struct buffer_head *get_block_length(struct super_block *sb,
  34                         u64 *cur_index, int *offset, int *length)
  35 {
  36         struct squashfs_sb_info *msblk = sb->s_fs_info;
  37         struct buffer_head *bh;
  38 
  39         bh = sb_bread(sb, *cur_index);
  40         if (bh == NULL)
  41                 return NULL;
  42 
  43         if (msblk->devblksize - *offset == 1) {
  44                 *length = (unsigned char) bh->b_data[*offset];
  45                 put_bh(bh);
  46                 bh = sb_bread(sb, ++(*cur_index));
  47                 if (bh == NULL)
  48                         return NULL;
  49                 *length |= (unsigned char) bh->b_data[0] << 8;
  50                 *offset = 1;
  51         } else {
  52                 *length = (unsigned char) bh->b_data[*offset] |
  53                         (unsigned char) bh->b_data[*offset + 1] << 8;
  54                 *offset += 2;
  55 
  56                 if (*offset == msblk->devblksize) {
  57                         put_bh(bh);
  58                         bh = sb_bread(sb, ++(*cur_index));
  59                         if (bh == NULL)
  60                                 return NULL;
  61                         *offset = 0;
  62                 }
  63         }
  64 
  65         return bh;
  66 }
  67 
  68 
  69 /*
  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
  76  * algorithms).
  77  */
  78 int squashfs_read_data(struct super_block *sb, u64 index, int length,
  79                 u64 *next_index, struct squashfs_page_actor *output)
  80 {
  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;
  86 
  87         bh = kcalloc(((output->length + msblk->devblksize - 1)
  88                 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
  89         if (bh == NULL)
  90                 return -ENOMEM;
  91 
  92         if (length) {
  93                 /*
  94                  * Datablock.
  95                  */
  96                 bytes = -offset;
  97                 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
  98                 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
  99                 if (next_index)
 100                         *next_index = index + length;
 101 
 102                 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 103                         index, compressed ? "" : "un", length, output->length);
 104 
 105                 if (length < 0 || length > output->length ||
 106                                 (index + length) > msblk->bytes_used)
 107                         goto read_failure;
 108 
 109                 for (b = 0; bytes < length; b++, cur_index++) {
 110                         bh[b] = sb_getblk(sb, cur_index);
 111                         if (bh[b] == NULL)
 112                                 goto block_release;
 113                         bytes += msblk->devblksize;
 114                 }
 115                 ll_rw_block(REQ_OP_READ, 0, b, bh);
 116         } else {
 117                 /*
 118                  * Metadata block.
 119                  */
 120                 if ((index + 2) > msblk->bytes_used)
 121                         goto read_failure;
 122 
 123                 bh[0] = get_block_length(sb, &cur_index, &offset, &length);
 124                 if (bh[0] == NULL)
 125                         goto read_failure;
 126                 b = 1;
 127 
 128                 bytes = msblk->devblksize - offset;
 129                 compressed = SQUASHFS_COMPRESSED(length);
 130                 length = SQUASHFS_COMPRESSED_SIZE(length);
 131                 if (next_index)
 132                         *next_index = index + length + 2;
 133 
 134                 TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
 135                                 compressed ? "" : "un", length);
 136 
 137                 if (length < 0 || length > output->length ||
 138                                         (index + length) > msblk->bytes_used)
 139                         goto block_release;
 140 
 141                 for (; bytes < length; b++) {
 142                         bh[b] = sb_getblk(sb, ++cur_index);
 143                         if (bh[b] == NULL)
 144                                 goto block_release;
 145                         bytes += msblk->devblksize;
 146                 }
 147                 ll_rw_block(REQ_OP_READ, 0, b - 1, bh + 1);
 148         }
 149 
 150         for (i = 0; i < b; i++) {
 151                 wait_on_buffer(bh[i]);
 152                 if (!buffer_uptodate(bh[i]))
 153                         goto block_release;
 154         }
 155 
 156         if (compressed) {
 157                 if (!msblk->stream)
 158                         goto read_failure;
 159                 length = squashfs_decompress(msblk, bh, b, offset, length,
 160                         output);
 161                 if (length < 0)
 162                         goto read_failure;
 163         } else {
 164                 /*
 165                  * Block is uncompressed.
 166                  */
 167                 int in, pg_offset = 0;
 168                 void *data = squashfs_first_page(output);
 169 
 170                 for (bytes = length; k < b; k++) {
 171                         in = min(bytes, msblk->devblksize - offset);
 172                         bytes -= in;
 173                         while (in) {
 174                                 if (pg_offset == PAGE_SIZE) {
 175                                         data = squashfs_next_page(output);
 176                                         pg_offset = 0;
 177                                 }
 178                                 avail = min_t(int, in, PAGE_SIZE -
 179                                                 pg_offset);
 180                                 memcpy(data + pg_offset, bh[k]->b_data + offset,
 181                                                 avail);
 182                                 in -= avail;
 183                                 pg_offset += avail;
 184                                 offset += avail;
 185                         }
 186                         offset = 0;
 187                         put_bh(bh[k]);
 188                 }
 189                 squashfs_finish_page(output);
 190         }
 191 
 192         kfree(bh);
 193         return length;
 194 
 195 block_release:
 196         for (; k < b; k++)
 197                 put_bh(bh[k]);
 198 
 199 read_failure:
 200         ERROR("squashfs_read_data failed to read block 0x%llx\n",
 201                                         (unsigned long long) index);
 202         kfree(bh);
 203         return -EIO;
 204 }
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root/fs/squashfs/block.c

DEFINITIONS
