fs/squashfs/block.c

   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/blkdev.h>
  17 #include <linux/fs.h>
  18 #include <linux/vfs.h>
  19 #include <linux/slab.h>
  20 #include <linux/pagemap.h>
  21 #include <linux/string.h>
  22 #include <linux/bio.h>
  23
  24 #include "squashfs_fs.h"
  25 #include "squashfs_fs_sb.h"
  26 #include "squashfs.h"
  27 #include "decompressor.h"
  28 #include "page_actor.h"
  29
  30 /*
  31  * Returns the amount of bytes copied to the page actor.
  32  */
  33 static int copy_bio_to_actor(struct bio *bio,
  34                              struct squashfs_page_actor *actor,
  35                              int offset, int req_length)
  36 {
  37         void *actor_addr;
  38         struct bvec_iter_all iter_all = {};
  39         struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
  40         int copied_bytes = 0;
  41         int actor_offset = 0;
  42
  43         squashfs_actor_nobuff(actor);
  44         actor_addr = squashfs_first_page(actor);
  45
  46         if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all)))
  47                 return 0;
  48
  49         while (copied_bytes < req_length) {
  50                 int bytes_to_copy = min_t(int, bvec->bv_len - offset,
  51                                           PAGE_SIZE - actor_offset);
  52
  53                 bytes_to_copy = min_t(int, bytes_to_copy,
  54                                       req_length - copied_bytes);
  55                 if (!IS_ERR(actor_addr))
  56                         memcpy(actor_addr + actor_offset, bvec_virt(bvec) +
  57                                         offset, bytes_to_copy);
  58
  59                 actor_offset += bytes_to_copy;
  60                 copied_bytes += bytes_to_copy;
  61                 offset += bytes_to_copy;
  62
  63                 if (actor_offset >= PAGE_SIZE) {
  64                         actor_addr = squashfs_next_page(actor);
  65                         if (!actor_addr)
  66                                 break;
  67                         actor_offset = 0;
  68                 }
  69                 if (offset >= bvec->bv_len) {
  70                         if (!bio_next_segment(bio, &iter_all))
  71                                 break;
  72                         offset = 0;
  73                 }
  74         }
  75         squashfs_finish_page(actor);
  76         return copied_bytes;
  77 }
  78
  79 static int squashfs_bio_read_cached(struct bio *fullbio,
  80                 struct address_space *cache_mapping, u64 index, int length,
  81                 u64 read_start, u64 read_end, int page_count)
  82 {
  83         struct page *head_to_cache = NULL, *tail_to_cache = NULL;
  84         struct block_device *bdev = fullbio->bi_bdev;
  85         int start_idx = 0, end_idx = 0;
  86         struct bvec_iter_all iter_all;
  87         struct bio *bio = NULL;
  88         struct bio_vec *bv;
  89         int idx = 0;
  90         int err = 0;
  91
  92         bio_for_each_segment_all(bv, fullbio, iter_all) {
  93                 struct page *page = bv->bv_page;
  94
  95                 if (page->mapping == cache_mapping) {
  96                         idx++;
  97                         continue;
  98                 }
  99
 100                 /*
 101                  * We only use this when the device block size is the same as
 102                  * the page size, so read_start and read_end cover full pages.
 103                  *
 104                  * Compare these to the original required index and length to
 105                  * only cache pages which were requested partially, since these
 106                  * are the ones which are likely to be needed when reading
 107                  * adjacent blocks.
 108                  */
 109                 if (idx == 0 && index != read_start)
 110                         head_to_cache = page;
 111                 else if (idx == page_count - 1 && index + length != read_end)
 112                         tail_to_cache = page;
 113
 114                 if (!bio || idx != end_idx) {
 115                         struct bio *new = bio_alloc_clone(bdev, fullbio,
 116                                                           GFP_NOIO, &fs_bio_set);
 117
 118                         if (bio) {
 119                                 bio_trim(bio, start_idx * PAGE_SECTORS,
 120                                          (end_idx - start_idx) * PAGE_SECTORS);
 121                                 bio_chain(bio, new);
 122                                 submit_bio(bio);
 123                         }
 124
 125                         bio = new;
 126                         start_idx = idx;
 127                 }
 128
 129                 idx++;
 130                 end_idx = idx;
 131         }
 132
 133         if (bio) {
 134                 bio_trim(bio, start_idx * PAGE_SECTORS,
 135                          (end_idx - start_idx) * PAGE_SECTORS);
 136                 err = submit_bio_wait(bio);
 137                 bio_put(bio);
 138         }
 139
 140         if (err)
 141                 return err;
 142
 143         if (head_to_cache) {
 144                 int ret = add_to_page_cache_lru(head_to_cache, cache_mapping,
 145                                                 read_start >> PAGE_SHIFT,
 146                                                 GFP_NOIO);
 147
 148                 if (!ret) {
 149                         SetPageUptodate(head_to_cache);
 150                         unlock_page(head_to_cache);
 151                 }
 152
 153         }
 154
 155         if (tail_to_cache) {
 156                 int ret = add_to_page_cache_lru(tail_to_cache, cache_mapping,
 157                                                 (read_end >> PAGE_SHIFT) - 1,
 158                                                 GFP_NOIO);
 159
 160                 if (!ret) {
 161                         SetPageUptodate(tail_to_cache);
 162                         unlock_page(tail_to_cache);
 163                 }
 164         }
 165
 166         return 0;
 167 }
 168
 169 static struct page *squashfs_get_cache_page(struct address_space *mapping,
 170                                             pgoff_t index)
 171 {
 172         struct page *page;
 173
 174         if (!mapping)
 175                 return NULL;
 176
 177         page = find_get_page(mapping, index);
 178         if (!page)
 179                 return NULL;
 180
 181         if (!PageUptodate(page)) {
 182                 put_page(page);
 183                 return NULL;
 184         }
 185
 186         return page;
 187 }
 188
 189 static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
 190                              struct bio **biop, int *block_offset)
 191 {
 192         struct squashfs_sb_info *msblk = sb->s_fs_info;
 193         struct address_space *cache_mapping = msblk->cache_mapping;
 194         const u64 read_start = round_down(index, msblk->devblksize);
 195         const sector_t block = read_start >> msblk->devblksize_log2;
 196         const u64 read_end = round_up(index + length, msblk->devblksize);
 197         const sector_t block_end = read_end >> msblk->devblksize_log2;
 198         int offset = read_start - round_down(index, PAGE_SIZE);
 199         int total_len = (block_end - block) << msblk->devblksize_log2;
 200         const int page_count = DIV_ROUND_UP(total_len + offset, PAGE_SIZE);
 201         int error, i;
 202         struct bio *bio;
 203
 204         bio = bio_kmalloc(page_count, GFP_NOIO);
 205         if (!bio)
 206                 return -ENOMEM;
 207         bio_init(bio, sb->s_bdev, bio->bi_inline_vecs, page_count, REQ_OP_READ);
 208         bio->bi_iter.bi_sector = block * (msblk->devblksize >> SECTOR_SHIFT);
 209
 210         for (i = 0; i < page_count; ++i) {
 211                 unsigned int len =
 212                         min_t(unsigned int, PAGE_SIZE - offset, total_len);
 213                 pgoff_t index = (read_start >> PAGE_SHIFT) + i;
 214                 struct page *page;
 215
 216                 page = squashfs_get_cache_page(cache_mapping, index);
 217                 if (!page)
 218                         page = alloc_page(GFP_NOIO);
 219
 220                 if (!page) {
 221                         error = -ENOMEM;
 222                         goto out_free_bio;
 223                 }
 224
 225                 /*
 226                  * Use the __ version to avoid merging since we need each page
 227                  * to be separate when we check for and avoid cached pages.
 228                  */
 229                 __bio_add_page(bio, page, len, offset);
 230                 offset = 0;
 231                 total_len -= len;
 232         }
 233
 234         if (cache_mapping)
 235                 error = squashfs_bio_read_cached(bio, cache_mapping, index,
 236                                                  length, read_start, read_end,
 237                                                  page_count);
 238         else
 239                 error = submit_bio_wait(bio);
 240         if (error)
 241                 goto out_free_bio;
 242
 243         *biop = bio;
 244         *block_offset = index & ((1 << msblk->devblksize_log2) - 1);
 245         return 0;
 246
 247 out_free_bio:
 248         bio_free_pages(bio);
 249         bio_uninit(bio);
 250         kfree(bio);
 251         return error;
 252 }
 253
 254 /*
 255  * Read and decompress a metadata block or datablock.  Length is non-zero
 256  * if a datablock is being read (the size is stored elsewhere in the
 257  * filesystem), otherwise the length is obtained from the first two bytes of
 258  * the metadata block.  A bit in the length field indicates if the block
 259  * is stored uncompressed in the filesystem (usually because compression
 260  * generated a larger block - this does occasionally happen with compression
 261  * algorithms).
 262  */
 263 int squashfs_read_data(struct super_block *sb, u64 index, int length,
 264                        u64 *next_index, struct squashfs_page_actor *output)
 265 {
 266         struct squashfs_sb_info *msblk = sb->s_fs_info;
 267         struct bio *bio = NULL;
 268         int compressed;
 269         int res;
 270         int offset;
 271
 272         if (length) {
 273                 /*
 274                  * Datablock.
 275                  */
 276                 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 277                 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 278                 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 279                         index, compressed ? "" : "un", length, output->length);
 280         } else {
 281                 /*
 282                  * Metadata block.
 283                  */
 284                 const u8 *data;
 285                 struct bvec_iter_all iter_all = {};
 286                 struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
 287
 288                 if (index + 2 > msblk->bytes_used) {
 289                         res = -EIO;
 290                         goto out;
 291                 }
 292                 res = squashfs_bio_read(sb, index, 2, &bio, &offset);
 293                 if (res)
 294                         goto out;
 295
 296                 if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
 297                         res = -EIO;
 298                         goto out_free_bio;
 299                 }
 300                 /* Extract the length of the metadata block */
 301                 data = bvec_virt(bvec);
 302                 length = data[offset];
 303                 if (offset < bvec->bv_len - 1) {
 304                         length |= data[offset + 1] << 8;
 305                 } else {
 306                         if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
 307                                 res = -EIO;
 308                                 goto out_free_bio;
 309                         }
 310                         data = bvec_virt(bvec);
 311                         length |= data[0] << 8;
 312                 }
 313                 bio_free_pages(bio);
 314                 bio_uninit(bio);
 315                 kfree(bio);
 316
 317                 compressed = SQUASHFS_COMPRESSED(length);
 318                 length = SQUASHFS_COMPRESSED_SIZE(length);
 319                 index += 2;
 320
 321                 TRACE("Block @ 0x%llx, %scompressed size %d\n", index - 2,
 322                       compressed ? "" : "un", length);
 323         }
 324         if (length <= 0 || length > output->length ||
 325                         (index + length) > msblk->bytes_used) {
 326                 res = -EIO;
 327                 goto out;
 328         }
 329
 330         if (next_index)
 331                 *next_index = index + length;
 332
 333         res = squashfs_bio_read(sb, index, length, &bio, &offset);
 334         if (res)
 335                 goto out;
 336
 337         if (compressed) {
 338                 if (!msblk->stream) {
 339                         res = -EIO;
 340                         goto out_free_bio;
 341                 }
 342                 res = msblk->thread_ops->decompress(msblk, bio, offset, length, output);
 343         } else {
 344                 res = copy_bio_to_actor(bio, output, offset, length);
 345         }
 346
 347 out_free_bio:
 348         bio_free_pages(bio);
 349         bio_uninit(bio);
 350         kfree(bio);
 351 out:
 352         if (res < 0) {
 353                 ERROR("Failed to read block 0x%llx: %d\n", index, res);
 354                 if (msblk->panic_on_errors)
 355                         panic("squashfs read failed");
 356         }
 357
 358         return res;
 359 }