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mkfs_ext2: explain why 0.5G+ images are a bit different

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2009-10-21 00:34:27 +02:00
parent 5e1dbd5bc3
commit 2288d86a54
1 changed files with 11 additions and 4 deletions
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15
util-linux/mkfs_ext2.c
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@ -309,20 +309,23 @@ int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv)
{
// N.B. e2fsprogs does as follows!
// ninodes is the total number of inodes (files) in the file system
uint32_t ninodes = ((uint64_t) nblocks_full * blocksize) / bytes_per_inode;
uint32_t overhead, remainder;
// ninodes is the max number of inodes in this filesystem
uint32_t ninodes = ((uint64_t) nblocks_full * blocksize) / bytes_per_inode;
if (ninodes < EXT2_GOOD_OLD_FIRST_INO+1)
ninodes = EXT2_GOOD_OLD_FIRST_INO+1;
inodes_per_group = div_roundup(ninodes, ngroups);
// minimum number because the first EXT2_GOOD_OLD_FIRST_INO-1 are reserved
if (inodes_per_group < 16)
inodes_per_group = 16;
// a block group can have no more than 8*blocksize inodes
// a block group can't have more inodes than blocks
if (inodes_per_group > blocks_per_group)
inodes_per_group = blocks_per_group;
// adjust inodes per group so they completely fill the inode table blocks in the descriptor
//incompatibility on images >= 0.5GB:
//difference in sizeof(*inode) sometimes
//results in slightly bigger inodes_per_group here
//compared to standard mke2fs:
inodes_per_group = (div_roundup(inodes_per_group * sizeof(*inode), blocksize) * blocksize) / sizeof(*inode);
// make sure the number of inodes per group is a multiple of 8
inodes_per_group &= ~7;
@ -345,6 +348,7 @@ int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv)
////) {
//// bb_error_msg_and_die("way small device");
////}
// Standard mke2fs uses 50. Looks like a bug in our calculation
// of "remainder" or "overhead" - we don't match standard mke2fs
// when we transition from one group to two groups
@ -414,6 +418,9 @@ int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv)
sb = xzalloc(1024);
STORE_LE(sb->s_rev_level, 1); // revision 1 filesystem
STORE_LE(sb->s_magic, EXT2_SUPER_MAGIC);
//incompatibility:
//on images > 0.5GB, standard mke2fs uses 256 byte inodes.
//we always use 128 byte ones:
STORE_LE(sb->s_inode_size, sizeof(*inode));
STORE_LE(sb->s_first_ino, EXT2_GOOD_OLD_FIRST_INO);
STORE_LE(sb->s_log_block_size, blocksize_log2 - EXT2_MIN_BLOCK_LOG_SIZE);