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| author | Denys Vlasenko <vda.linux@googlemail.com> | 2009-10-21 00:34:27 +0200 |
|---|---|---|
| committer | Denys Vlasenko <vda.linux@googlemail.com> | 2009-10-21 00:34:27 +0200 |
| commit | 2288d86a54eee81800bdadea6f603ad4e234efb1 (patch) | |
| tree | 0639a8d9a58b0e913fb4cf090a141154555231f4 /util-linux/mkfs_ext2.c | |
| parent | 5e1dbd5bc3c609c73037a41546c5ead240821558 (diff) | |
| download | busybox-w32-2288d86a54eee81800bdadea6f603ad4e234efb1.tar.gz busybox-w32-2288d86a54eee81800bdadea6f603ad4e234efb1.tar.bz2 busybox-w32-2288d86a54eee81800bdadea6f603ad4e234efb1.zip | |
mkfs_ext2: explain why 0.5G+ images are a bit different
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'util-linux/mkfs_ext2.c')
| -rw-r--r-- | util-linux/mkfs_ext2.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/util-linux/mkfs_ext2.c b/util-linux/mkfs_ext2.c index be9e36332..de4c8b6c6 100644 --- a/util-linux/mkfs_ext2.c +++ b/util-linux/mkfs_ext2.c | |||
| @@ -309,20 +309,23 @@ int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv) | |||
| 309 | 309 | ||
| 310 | { | 310 | { |
| 311 | // N.B. e2fsprogs does as follows! | 311 | // N.B. e2fsprogs does as follows! |
| 312 | // ninodes is the total number of inodes (files) in the file system | ||
| 313 | uint32_t ninodes = ((uint64_t) nblocks_full * blocksize) / bytes_per_inode; | ||
| 314 | uint32_t overhead, remainder; | 312 | uint32_t overhead, remainder; |
| 313 | // ninodes is the max number of inodes in this filesystem | ||
| 314 | uint32_t ninodes = ((uint64_t) nblocks_full * blocksize) / bytes_per_inode; | ||
| 315 | if (ninodes < EXT2_GOOD_OLD_FIRST_INO+1) | 315 | if (ninodes < EXT2_GOOD_OLD_FIRST_INO+1) |
| 316 | ninodes = EXT2_GOOD_OLD_FIRST_INO+1; | 316 | ninodes = EXT2_GOOD_OLD_FIRST_INO+1; |
| 317 | inodes_per_group = div_roundup(ninodes, ngroups); | 317 | inodes_per_group = div_roundup(ninodes, ngroups); |
| 318 | // minimum number because the first EXT2_GOOD_OLD_FIRST_INO-1 are reserved | 318 | // minimum number because the first EXT2_GOOD_OLD_FIRST_INO-1 are reserved |
| 319 | if (inodes_per_group < 16) | 319 | if (inodes_per_group < 16) |
| 320 | inodes_per_group = 16; | 320 | inodes_per_group = 16; |
| 321 | 321 | // a block group can't have more inodes than blocks | |
| 322 | // a block group can have no more than 8*blocksize inodes | ||
| 323 | if (inodes_per_group > blocks_per_group) | 322 | if (inodes_per_group > blocks_per_group) |
| 324 | inodes_per_group = blocks_per_group; | 323 | inodes_per_group = blocks_per_group; |
| 325 | // adjust inodes per group so they completely fill the inode table blocks in the descriptor | 324 | // adjust inodes per group so they completely fill the inode table blocks in the descriptor |
| 325 | //incompatibility on images >= 0.5GB: | ||
| 326 | //difference in sizeof(*inode) sometimes | ||
| 327 | //results in slightly bigger inodes_per_group here | ||
| 328 | //compared to standard mke2fs: | ||
| 326 | inodes_per_group = (div_roundup(inodes_per_group * sizeof(*inode), blocksize) * blocksize) / sizeof(*inode); | 329 | inodes_per_group = (div_roundup(inodes_per_group * sizeof(*inode), blocksize) * blocksize) / sizeof(*inode); |
| 327 | // make sure the number of inodes per group is a multiple of 8 | 330 | // make sure the number of inodes per group is a multiple of 8 |
| 328 | inodes_per_group &= ~7; | 331 | inodes_per_group &= ~7; |
| @@ -345,6 +348,7 @@ int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv) | |||
| 345 | ////) { | 348 | ////) { |
| 346 | //// bb_error_msg_and_die("way small device"); | 349 | //// bb_error_msg_and_die("way small device"); |
| 347 | ////} | 350 | ////} |
| 351 | |||
| 348 | // Standard mke2fs uses 50. Looks like a bug in our calculation | 352 | // Standard mke2fs uses 50. Looks like a bug in our calculation |
| 349 | // of "remainder" or "overhead" - we don't match standard mke2fs | 353 | // of "remainder" or "overhead" - we don't match standard mke2fs |
| 350 | // when we transition from one group to two groups | 354 | // when we transition from one group to two groups |
| @@ -414,6 +418,9 @@ int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv) | |||
| 414 | sb = xzalloc(1024); | 418 | sb = xzalloc(1024); |
| 415 | STORE_LE(sb->s_rev_level, 1); // revision 1 filesystem | 419 | STORE_LE(sb->s_rev_level, 1); // revision 1 filesystem |
| 416 | STORE_LE(sb->s_magic, EXT2_SUPER_MAGIC); | 420 | STORE_LE(sb->s_magic, EXT2_SUPER_MAGIC); |
| 421 | //incompatibility: | ||
| 422 | //on images > 0.5GB, standard mke2fs uses 256 byte inodes. | ||
| 423 | //we always use 128 byte ones: | ||
| 417 | STORE_LE(sb->s_inode_size, sizeof(*inode)); | 424 | STORE_LE(sb->s_inode_size, sizeof(*inode)); |
| 418 | STORE_LE(sb->s_first_ino, EXT2_GOOD_OLD_FIRST_INO); | 425 | STORE_LE(sb->s_first_ino, EXT2_GOOD_OLD_FIRST_INO); |
| 419 | STORE_LE(sb->s_log_block_size, blocksize_log2 - EXT2_MIN_BLOCK_LOG_SIZE); | 426 | STORE_LE(sb->s_log_block_size, blocksize_log2 - EXT2_MIN_BLOCK_LOG_SIZE); |