3.3. Block and inode Bitmaps¶
The data block bitmap tracks the usage of data blocks within the block group.
The inode bitmap records which entries in the inode table are in use.
As with most bitmaps, one bit represents the usage status of one data block or inode table entry. This implies a block group size of 8 * number_of_bytes_in_a_logical_block.
NOTE: If BLOCK_UNINIT
is set for a given block group, various parts
of the kernel and e2fsprogs code pretends that the block bitmap contains
zeros (i.e. all blocks in the group are free). However, it is not
necessarily the case that no blocks are in use -- if meta_bg
is set,
the bitmaps and group descriptor live inside the group. Unfortunately,
ext2fs_test_block_bitmap2()
will return ‘0’ for those locations,
which produces confusing debugfs output.