lib/ext2fs/openfs.c

   1 /*
   2  * openfs.c --- open an ext2 filesystem
   3  *
   4  * Copyright (C) 1993, 1994, 1995, 1996 Theodore Ts'o.
   5  *
   6  * %Begin-Header%
   7  * This file may be redistributed under the terms of the GNU Library
   8  * General Public License, version 2.
   9  * %End-Header%
  10  */
  11
  12 #include "config.h"
  13 #include <stdio.h>
  14 #include <string.h>
  15 #if HAVE_UNISTD_H
  16 #include <unistd.h>
  17 #endif
  18 #include <fcntl.h>
  19 #include <time.h>
  20 #if HAVE_SYS_STAT_H
  21 #include <sys/stat.h>
  22 #endif
  23 #if HAVE_SYS_TYPES_H
  24 #include <sys/types.h>
  25 #endif
  26 #ifdef HAVE_ERRNO_H
  27 #include <errno.h>
  28 #endif
  29
  30 #include "ext2_fs.h"
  31
  32 #include "ext2fs.h"
  33 #include "e2image.h"
  34
  35 blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block,
  36                                      dgrp_t i)
  37 {
  38         int     bg;
  39         int     has_super = 0, group_zero_adjust = 0;
  40         blk64_t ret_blk;
  41
  42         /*
  43          * On a bigalloc FS with 1K blocks, block 0 is reserved for non-ext4
  44          * stuff, so adjust for that if we're being asked for group 0.
  45          */
  46         if (i == 0 && fs->blocksize == 1024 && EXT2FS_CLUSTER_RATIO(fs) > 1)
  47                 group_zero_adjust = 1;
  48
  49         if (!ext2fs_has_feature_meta_bg(fs->super) ||
  50             (i < fs->super->s_first_meta_bg))
  51                 return group_block + i + 1 + group_zero_adjust;
  52
  53         bg = EXT2_DESC_PER_BLOCK(fs->super) * i;
  54         if (ext2fs_bg_has_super(fs, bg))
  55                 has_super = 1;
  56         ret_blk = ext2fs_group_first_block2(fs, bg);
  57         /*
  58          * If group_block is not the normal value, we're trying to use
  59          * the backup group descriptors and superblock --- so use the
  60          * alternate location of the second block group in the
  61          * metablock group.  Ideally we should be testing each bg
  62          * descriptor block individually for correctness, but we don't
  63          * have the infrastructure in place to do that.
  64          */
  65         if (group_block != fs->super->s_first_data_block &&
  66             ((ret_blk + has_super + fs->super->s_blocks_per_group) <
  67              ext2fs_blocks_count(fs->super))) {
  68                 ret_blk += fs->super->s_blocks_per_group;
  69
  70                 /*
  71                  * If we're going to jump forward a block group, make sure
  72                  * that we adjust has_super to account for the next group's
  73                  * backup superblock (or lack thereof).
  74                  */
  75                 if (ext2fs_bg_has_super(fs, bg + 1))
  76                         has_super = 1;
  77                 else
  78                         has_super = 0;
  79         }
  80         return ret_blk + has_super + group_zero_adjust;
  81 }
  82
  83 blk_t ext2fs_descriptor_block_loc(ext2_filsys fs, blk_t group_block, dgrp_t i)
  84 {
  85         return ext2fs_descriptor_block_loc2(fs, group_block, i);
  86 }
  87
  88 errcode_t ext2fs_open(const char *name, int flags, int superblock,
  89                       unsigned int block_size, io_manager manager,
  90                       ext2_filsys *ret_fs)
  91 {
  92         return ext2fs_open2(name, 0, flags, superblock, block_size,
  93                             manager, ret_fs);
  94 }
  95
  96 static void block_sha_map_free_entry(void *data)
  97 {
  98         free(data);
  99         return;
 100 }
 101
 102 /*
 103  *  Note: if superblock is non-zero, block-size must also be non-zero.
 104  *      Superblock and block_size can be zero to use the default size.
 105  *
 106  * Valid flags for ext2fs_open()
 107  *
 108  *      EXT2_FLAG_RW    - Open the filesystem for read/write.
 109  *      EXT2_FLAG_FORCE - Open the filesystem even if some of the
 110  *                              features aren't supported.
 111  *      EXT2_FLAG_JOURNAL_DEV_OK - Open an ext3 journal device
 112  *      EXT2_FLAG_SKIP_MMP - Open without multi-mount protection check.
 113  *      EXT2_FLAG_64BITS - Allow 64-bit bitfields (needed for large
 114  *                              filesystems)
 115  */
 116 errcode_t ext2fs_open2(const char *name, const char *io_options,
 117                        int flags, int superblock,
 118                        unsigned int block_size, io_manager manager,
 119                        ext2_filsys *ret_fs)
 120 {
 121         ext2_filsys     fs;
 122         errcode_t       retval;
 123         unsigned long   i, first_meta_bg;
 124         __u32           features;
 125         unsigned int    blocks_per_group, io_flags;
 126         blk64_t         group_block, blk;
 127         char            *dest, *cp;
 128         int             group_zero_adjust = 0;
 129         unsigned int    inode_size;
 130         __u64           groups_cnt;
 131 #ifdef WORDS_BIGENDIAN
 132         unsigned int    groups_per_block;
 133         struct ext2_group_desc *gdp;
 134         int             j;
 135 #endif
 136         char            *time_env;
 137         int             csum_retries = 0;
 138
 139         EXT2_CHECK_MAGIC(manager, EXT2_ET_MAGIC_IO_MANAGER);
 140
 141         retval = ext2fs_get_mem(sizeof(struct struct_ext2_filsys), &fs);
 142         if (retval)
 143                 return retval;
 144
 145         memset(fs, 0, sizeof(struct struct_ext2_filsys));
 146         fs->magic = EXT2_ET_MAGIC_EXT2FS_FILSYS;
 147         fs->flags = flags;
 148         /* don't overwrite sb backups unless flag is explicitly cleared */
 149         fs->flags |= EXT2_FLAG_MASTER_SB_ONLY;
 150         fs->umask = 022;
 151
 152         time_env = getenv("E2FSPROGS_FAKE_TIME");
 153         if (time_env)
 154                 fs->now = strtoul(time_env, NULL, 0);
 155
 156         retval = ext2fs_get_mem(strlen(name)+1, &fs->device_name);
 157         if (retval)
 158                 goto cleanup;
 159         strcpy(fs->device_name, name);
 160         cp = strchr(fs->device_name, '?');
 161         if (!io_options && cp) {
 162                 *cp++ = 0;
 163                 io_options = cp;
 164         }
 165
 166         io_flags = 0;
 167         if (flags & EXT2_FLAG_RW)
 168                 io_flags |= IO_FLAG_RW;
 169         if (flags & EXT2_FLAG_EXCLUSIVE)
 170                 io_flags |= IO_FLAG_EXCLUSIVE;
 171         if (flags & EXT2_FLAG_DIRECT_IO)
 172                 io_flags |= IO_FLAG_DIRECT_IO;
 173         if (flags & EXT2_FLAG_THREADS)
 174                 io_flags |= IO_FLAG_THREADS;
 175         retval = manager->open(fs->device_name, io_flags, &fs->io);
 176         if (retval)
 177                 goto cleanup;
 178         if (io_options &&
 179             (retval = io_channel_set_options(fs->io, io_options)))
 180                 goto cleanup;
 181         fs->image_io = fs->io;
 182         fs->io->app_data = fs;
 183         retval = io_channel_alloc_buf(fs->io, -SUPERBLOCK_SIZE, &fs->super);
 184         if (retval)
 185                 goto cleanup;
 186         if (flags & EXT2_FLAG_IMAGE_FILE) {
 187                 retval = ext2fs_get_mem(sizeof(struct ext2_image_hdr),
 188                                         &fs->image_header);
 189                 if (retval)
 190                         goto cleanup;
 191                 retval = io_channel_read_blk(fs->io, 0,
 192                                              -(int)sizeof(struct ext2_image_hdr),
 193                                              fs->image_header);
 194                 if (retval)
 195                         goto cleanup;
 196                 if (ext2fs_le32_to_cpu(fs->image_header->magic_number) != EXT2_ET_MAGIC_E2IMAGE)
 197                         return EXT2_ET_MAGIC_E2IMAGE;
 198                 superblock = 1;
 199                 block_size = ext2fs_le32_to_cpu(fs->image_header->fs_blocksize);
 200         }
 201
 202         /*
 203          * If the user specifies a specific block # for the
 204          * superblock, then he/she must also specify the block size!
 205          * Otherwise, read the master superblock located at offset
 206          * SUPERBLOCK_OFFSET from the start of the partition.
 207          *
 208          * Note: we only save a backup copy of the superblock if we
 209          * are reading the superblock from the primary superblock location.
 210          */
 211         if (superblock) {
 212                 if (!block_size) {
 213                         retval = EXT2_ET_INVALID_ARGUMENT;
 214                         goto cleanup;
 215                 }
 216                 io_channel_set_blksize(fs->io, block_size);
 217                 group_block = superblock;
 218                 fs->orig_super = 0;
 219         } else {
 220                 io_channel_set_blksize(fs->io, SUPERBLOCK_OFFSET);
 221                 superblock = 1;
 222                 group_block = 0;
 223                 retval = ext2fs_get_mem(SUPERBLOCK_SIZE, &fs->orig_super);
 224                 if (retval)
 225                         goto cleanup;
 226         }
 227 retry:
 228         retval = io_channel_read_blk(fs->io, superblock, -SUPERBLOCK_SIZE,
 229                                      fs->super);
 230         if (retval)
 231                 goto cleanup;
 232         if (fs->orig_super)
 233                 memcpy(fs->orig_super, fs->super, SUPERBLOCK_SIZE);
 234
 235         if (!(fs->flags & EXT2_FLAG_IGNORE_CSUM_ERRORS)) {
 236                 retval = 0;
 237                 if (!ext2fs_verify_csum_type(fs, fs->super))
 238                         retval = EXT2_ET_UNKNOWN_CSUM;
 239                 if (!ext2fs_superblock_csum_verify(fs, fs->super)) {
 240                         if (csum_retries++ < 3)
 241                                 goto retry;
 242                         retval = EXT2_ET_SB_CSUM_INVALID;
 243                 }
 244         }
 245
 246 #ifdef WORDS_BIGENDIAN
 247         fs->flags |= EXT2_FLAG_SWAP_BYTES;
 248         ext2fs_swap_super(fs->super);
 249 #else
 250         if (fs->flags & EXT2_FLAG_SWAP_BYTES) {
 251                 retval = EXT2_ET_UNIMPLEMENTED;
 252                 goto cleanup;
 253         }
 254 #endif
 255
 256         if (fs->super->s_magic != EXT2_SUPER_MAGIC)
 257                 retval = EXT2_ET_BAD_MAGIC;
 258         if (retval)
 259                 goto cleanup;
 260
 261         if (fs->super->s_rev_level > EXT2_LIB_CURRENT_REV) {
 262                 retval = EXT2_ET_REV_TOO_HIGH;
 263                 goto cleanup;
 264         }
 265
 266         /*
 267          * Check for feature set incompatibility
 268          */
 269         if (!(flags & EXT2_FLAG_FORCE)) {
 270                 features = fs->super->s_feature_incompat;
 271 #ifdef EXT2_LIB_SOFTSUPP_INCOMPAT
 272                 if (flags & EXT2_FLAG_SOFTSUPP_FEATURES)
 273                         features &= ~EXT2_LIB_SOFTSUPP_INCOMPAT;
 274 #endif
 275                 if (features & ~EXT2_LIB_FEATURE_INCOMPAT_SUPP) {
 276                         retval = EXT2_ET_UNSUPP_FEATURE;
 277                         goto cleanup;
 278                 }
 279
 280                 features = fs->super->s_feature_ro_compat;
 281 #ifdef EXT2_LIB_SOFTSUPP_RO_COMPAT
 282                 if (flags & EXT2_FLAG_SOFTSUPP_FEATURES)
 283                         features &= ~EXT2_LIB_SOFTSUPP_RO_COMPAT;
 284 #endif
 285                 if ((flags & EXT2_FLAG_RW) &&
 286                     (features & ~EXT2_LIB_FEATURE_RO_COMPAT_SUPP)) {
 287                         retval = EXT2_ET_RO_UNSUPP_FEATURE;
 288                         goto cleanup;
 289                 }
 290
 291                 if (!(flags & EXT2_FLAG_JOURNAL_DEV_OK) &&
 292                     ext2fs_has_feature_journal_dev(fs->super)) {
 293                         retval = EXT2_ET_UNSUPP_FEATURE;
 294                         goto cleanup;
 295                 }
 296         }
 297
 298         if ((fs->super->s_log_block_size >
 299              (unsigned) (EXT2_MAX_BLOCK_LOG_SIZE - EXT2_MIN_BLOCK_LOG_SIZE)) ||
 300             (fs->super->s_log_cluster_size >
 301              (unsigned) (EXT2_MAX_CLUSTER_LOG_SIZE - EXT2_MIN_CLUSTER_LOG_SIZE)) ||
 302             (fs->super->s_log_block_size > fs->super->s_log_cluster_size) ||
 303             (fs->super->s_log_groups_per_flex > 31)) {
 304                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 305                 goto cleanup;
 306         }
 307
 308         /*
 309          * bigalloc requires cluster-aware bitfield operations, which at the
 310          * moment means we need EXT2_FLAG_64BITS.
 311          */
 312         if (ext2fs_has_feature_bigalloc(fs->super) &&
 313             !(flags & EXT2_FLAG_64BITS)) {
 314                 retval = EXT2_ET_CANT_USE_LEGACY_BITMAPS;
 315                 goto cleanup;
 316         }
 317
 318         if (!ext2fs_has_feature_bigalloc(fs->super) &&
 319             (fs->super->s_log_block_size != fs->super->s_log_cluster_size)) {
 320                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 321                 goto cleanup;
 322         }
 323         fs->fragsize = fs->blocksize = EXT2_BLOCK_SIZE(fs->super);
 324         inode_size = EXT2_INODE_SIZE(fs->super);
 325         if ((inode_size < EXT2_GOOD_OLD_INODE_SIZE) ||
 326             (inode_size > fs->blocksize) ||
 327             (inode_size & (inode_size - 1))) {
 328                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 329                 goto cleanup;
 330         }
 331
 332         /* Enforce the block group descriptor size */
 333         if (!(flags & EXT2_FLAG_IGNORE_SB_ERRORS) &&
 334             ext2fs_has_feature_64bit(fs->super)) {
 335                 unsigned desc_size = fs->super->s_desc_size;
 336
 337                 if ((desc_size < EXT2_MIN_DESC_SIZE_64BIT) ||
 338                     (desc_size > EXT2_MAX_DESC_SIZE) ||
 339                     (desc_size & (desc_size - 1)) != 0) {
 340                         retval = EXT2_ET_BAD_DESC_SIZE;
 341                         goto cleanup;
 342                 }
 343         }
 344
 345         fs->cluster_ratio_bits = fs->super->s_log_cluster_size -
 346                 fs->super->s_log_block_size;
 347         if (EXT2_BLOCKS_PER_GROUP(fs->super) !=
 348             EXT2_CLUSTERS_PER_GROUP(fs->super) << fs->cluster_ratio_bits) {
 349                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 350                 goto cleanup;
 351         }
 352         fs->inode_blocks_per_group = ((EXT2_INODES_PER_GROUP(fs->super) *
 353                                        EXT2_INODE_SIZE(fs->super) +
 354                                        EXT2_BLOCK_SIZE(fs->super) - 1) /
 355                                       EXT2_BLOCK_SIZE(fs->super));
 356         if (block_size) {
 357                 if (block_size != fs->blocksize) {
 358                         retval = EXT2_ET_UNEXPECTED_BLOCK_SIZE;
 359                         goto cleanup;
 360                 }
 361         }
 362         /*
 363          * Set the blocksize to the filesystem's blocksize.
 364          */
 365         io_channel_set_blksize(fs->io, fs->blocksize);
 366
 367         /*
 368          * If this is an external journal device, don't try to read
 369          * the group descriptors, because they're not there.
 370          */
 371         if (ext2fs_has_feature_journal_dev(fs->super)) {
 372                 fs->group_desc_count = 0;
 373                 *ret_fs = fs;
 374                 return 0;
 375         }
 376
 377         if (EXT2_INODES_PER_GROUP(fs->super) == 0) {
 378                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 379                 goto cleanup;
 380         }
 381         /* Precompute the FS UUID to seed other checksums */
 382         ext2fs_init_csum_seed(fs);
 383
 384         /*
 385          * Read group descriptors
 386          */
 387         blocks_per_group = EXT2_BLOCKS_PER_GROUP(fs->super);
 388         if (blocks_per_group == 0 ||
 389             blocks_per_group > EXT2_MAX_BLOCKS_PER_GROUP(fs->super) ||
 390             fs->inode_blocks_per_group > EXT2_MAX_INODES_PER_GROUP(fs->super) ||
 391            EXT2_DESC_PER_BLOCK(fs->super) == 0 ||
 392            fs->super->s_first_data_block >= ext2fs_blocks_count(fs->super)) {
 393                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 394                 goto cleanup;
 395         }
 396         groups_cnt = ext2fs_div64_ceil(ext2fs_blocks_count(fs->super) -
 397                                        fs->super->s_first_data_block,
 398                                        blocks_per_group);
 399         if (groups_cnt >> 32) {
 400                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 401                 goto cleanup;
 402         }
 403         fs->group_desc_count =  groups_cnt;
 404         if (!(flags & EXT2_FLAG_IGNORE_SB_ERRORS) &&
 405             (__u64)fs->group_desc_count * EXT2_INODES_PER_GROUP(fs->super) !=
 406             fs->super->s_inodes_count) {
 407                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 408                 goto cleanup;
 409         }
 410         fs->desc_blocks = ext2fs_div_ceil(fs->group_desc_count,
 411                                           EXT2_DESC_PER_BLOCK(fs->super));
 412         if (ext2fs_has_feature_meta_bg(fs->super) &&
 413             (fs->super->s_first_meta_bg > fs->desc_blocks) &&
 414             !(flags & EXT2_FLAG_IGNORE_SB_ERRORS)) {
 415                 retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 416                 goto cleanup;
 417         }
 418         if (flags & EXT2_FLAG_SUPER_ONLY)
 419                 goto skip_read_bg;
 420         retval = ext2fs_get_array(fs->desc_blocks, fs->blocksize,
 421                                 &fs->group_desc);
 422         if (retval)
 423                 goto cleanup;
 424         if (!group_block)
 425                 group_block = fs->super->s_first_data_block;
 426         /*
 427          * On a FS with a 1K blocksize, block 0 is reserved for bootloaders
 428          * so we must increment block numbers to any group 0 items.
 429          *
 430          * However, we cannot touch group_block directly because in the meta_bg
 431          * case, the ext2fs_descriptor_block_loc2() function will interpret
 432          * group_block != s_first_data_block to mean that we want to access the
 433          * backup group descriptors.  This is not what we want if the caller
 434          * set superblock == 0 (i.e. auto-detect the superblock), which is
 435          * what's going on here.
 436          */
 437         if (group_block == 0 && fs->blocksize == 1024)
 438                 group_zero_adjust = 1;
 439         dest = (char *) fs->group_desc;
 440 #ifdef WORDS_BIGENDIAN
 441         groups_per_block = EXT2_DESC_PER_BLOCK(fs->super);
 442 #endif
 443         if (ext2fs_has_feature_meta_bg(fs->super) &&
 444             !(flags & EXT2_FLAG_IMAGE_FILE)) {
 445                 first_meta_bg = fs->super->s_first_meta_bg;
 446                 if (first_meta_bg > fs->desc_blocks)
 447                         first_meta_bg = fs->desc_blocks;
 448         } else
 449                 first_meta_bg = fs->desc_blocks;
 450         if (first_meta_bg) {
 451                 retval = io_channel_read_blk(fs->io, group_block +
 452                                              group_zero_adjust + 1,
 453                                              first_meta_bg, dest);
 454                 if (retval)
 455                         goto cleanup;
 456 #ifdef WORDS_BIGENDIAN
 457                 gdp = (struct ext2_group_desc *) dest;
 458                 for (j=0; j < groups_per_block*first_meta_bg; j++) {
 459                         gdp = ext2fs_group_desc(fs, fs->group_desc, j);
 460                         if (gdp)
 461                                 ext2fs_swap_group_desc2(fs, gdp);
 462                 }
 463 #endif
 464                 dest += fs->blocksize*first_meta_bg;
 465         }
 466
 467         for (i = first_meta_bg ; i < fs->desc_blocks; i++) {
 468                 blk = ext2fs_descriptor_block_loc2(fs, group_block, i);
 469                 io_channel_cache_readahead(fs->io, blk, 1);
 470         }
 471
 472         for (i=first_meta_bg ; i < fs->desc_blocks; i++) {
 473                 blk = ext2fs_descriptor_block_loc2(fs, group_block, i);
 474                 retval = io_channel_read_blk64(fs->io, blk, 1, dest);
 475                 if (retval)
 476                         goto cleanup;
 477 #ifdef WORDS_BIGENDIAN
 478                 for (j=0; j < groups_per_block; j++) {
 479                         gdp = ext2fs_group_desc(fs, fs->group_desc,
 480                                                 i * groups_per_block + j);
 481                         if (gdp)
 482                                 ext2fs_swap_group_desc2(fs, gdp);
 483                 }
 484 #endif
 485                 dest += fs->blocksize;
 486         }
 487
 488         fs->stride = fs->super->s_raid_stride;
 489
 490         /*
 491          * If recovery is from backup superblock, Clear _UNININT flags &
 492          * reset bg_itable_unused to zero
 493          */
 494         if (superblock > 1 && ext2fs_has_group_desc_csum(fs)) {
 495                 dgrp_t group;
 496
 497                 for (group = 0; group < fs->group_desc_count; group++) {
 498                         ext2fs_bg_flags_clear(fs, group, EXT2_BG_BLOCK_UNINIT);
 499                         ext2fs_bg_flags_clear(fs, group, EXT2_BG_INODE_UNINIT);
 500                         ext2fs_bg_itable_unused_set(fs, group, 0);
 501                         /* The checksum will be reset later, but fix it here
 502                          * anyway to avoid printing a lot of spurious errors. */
 503                         ext2fs_group_desc_csum_set(fs, group);
 504                 }
 505                 if (fs->flags & EXT2_FLAG_RW)
 506                         ext2fs_mark_super_dirty(fs);
 507         }
 508 skip_read_bg:
 509         if (ext2fs_has_feature_mmp(fs->super) &&
 510             !(flags & EXT2_FLAG_SKIP_MMP) &&
 511             (flags & (EXT2_FLAG_RW | EXT2_FLAG_EXCLUSIVE))) {
 512                 retval = ext2fs_mmp_start(fs);
 513                 if (retval) {
 514                         fs->flags |= EXT2_FLAG_SKIP_MMP; /* just do cleanup */
 515                         ext2fs_mmp_stop(fs);
 516                         goto cleanup;
 517                 }
 518         }
 519
 520         if (fs->flags & EXT2_FLAG_SHARE_DUP) {
 521                 fs->block_sha_map = ext2fs_hashmap_create(ext2fs_djb2_hash,
 522                                         block_sha_map_free_entry, 4096);
 523                 if (!fs->block_sha_map) {
 524                         retval = EXT2_ET_NO_MEMORY;
 525                         goto cleanup;
 526                 }
 527                 ext2fs_set_feature_shared_blocks(fs->super);
 528         }
 529
 530         if (ext2fs_has_feature_casefold(fs->super))
 531                 fs->encoding = ext2fs_load_nls_table(fs->super->s_encoding);
 532
 533         fs->flags &= ~EXT2_FLAG_NOFREE_ON_ERROR;
 534         *ret_fs = fs;
 535
 536         return 0;
 537 cleanup:
 538         if (!(flags & EXT2_FLAG_NOFREE_ON_ERROR)) {
 539                 ext2fs_free(fs);
 540                 fs = NULL;
 541         }
 542         *ret_fs = fs;
 543         return retval;
 544 }
 545
 546 /*
 547  * Set/get the filesystem data I/O channel.
 548  *
 549  * These functions are only valid if EXT2_FLAG_IMAGE_FILE is true.
 550  */
 551 errcode_t ext2fs_get_data_io(ext2_filsys fs, io_channel *old_io)
 552 {
 553         if ((fs->flags & EXT2_FLAG_IMAGE_FILE) == 0)
 554                 return EXT2_ET_NOT_IMAGE_FILE;
 555         if (old_io) {
 556                 *old_io = (fs->image_io == fs->io) ? 0 : fs->io;
 557         }
 558         return 0;
 559 }
 560
 561 errcode_t ext2fs_set_data_io(ext2_filsys fs, io_channel new_io)
 562 {
 563         if ((fs->flags & EXT2_FLAG_IMAGE_FILE) == 0)
 564                 return EXT2_ET_NOT_IMAGE_FILE;
 565         fs->io = new_io ? new_io : fs->image_io;
 566         return 0;
 567 }
 568
 569 errcode_t ext2fs_rewrite_to_io(ext2_filsys fs, io_channel new_io)
 570 {
 571         errcode_t err;
 572
 573         if ((fs->flags & EXT2_FLAG_IMAGE_FILE) == 0)
 574                 return EXT2_ET_NOT_IMAGE_FILE;
 575         err = io_channel_set_blksize(new_io, fs->blocksize);
 576         if (err)
 577                 return err;
 578         if ((new_io == fs->image_io) || (new_io == fs->io))
 579                 return 0;
 580         if ((fs->image_io != fs->io) &&
 581             fs->image_io)
 582                 io_channel_close(fs->image_io);
 583         if (fs->io)
 584                 io_channel_close(fs->io);
 585         fs->io = fs->image_io = new_io;
 586         fs->flags |= EXT2_FLAG_DIRTY | EXT2_FLAG_RW |
 587                 EXT2_FLAG_BB_DIRTY | EXT2_FLAG_IB_DIRTY;
 588         fs->flags &= ~EXT2_FLAG_IMAGE_FILE;
 589         return 0;
 590 }