mke2fs: set upper limit to flex_bg count
mke2fs -G option allows root user to set flex_bg count (power of 2).
However ext4 has bad metadata layout if we specify more than or equal to
2^32 to mke2fs -G, because of the 32bit shift operation
in ext2fs_allocate_group_table().
And the maximum block group count of ext4 is 2^32 -1 (ext4_group_t
s_groups_count), so diallow more than 2^32 flex_bg count.
Steps to reproduce:
# mke2fs -t ext4 -G 4294967296 DEV
# dumpe2fs DEV
...
Flex block group size: 1 <----- flex_bg is 1!
...
Group 0: (Blocks 0-32767)
Checksum 0x4afd, unused inodes 7541
Primary superblock at 0, Group descriptors at 1-1
Reserved GDT blocks at 2-59
Block bitmap at 60 (+60), Inode bitmap at 61 (+61)
Inode table at 62-533 (+62)
32228 free blocks, 7541 free inodes, 2 directories, 7541 unused inodes
Free blocks: 540-32767
Free inodes: 12-7552
Group 1: (Blocks 32768-65535) [INODE_UNINIT]
Checksum 0xc890, unused inodes 7552
Backup superblock at 32768, Group descriptors at 32769-32769
Reserved GDT blocks at 32770-32827
Block bitmap at 32828 (+60), Inode bitmap at 32829 (+61)
Inode table at 32830-33301 (+62)
32234 free blocks, 7552 free inodes, 0 directories, 7552 unused inodes
Free blocks: 33302-65535
Free inodes: 7553-15104
...
Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: "Darrick J. Wong" <darrick.wong@oracle.com>
1 file changed