about the ext2 file system
 

For a block group on an ext2 file system, what's the relationship between "bg_free_blocks_count" field in the group descriptor and the block bitmap of the block group, or between "bg_free_inodes_count" field and the inode bitmap.
For example, for 4KB block size, each block bitmap has 4KB size describing 4KB*8=32768 blocks in a block group. Dose it mean that the number of bits set to "0" must equal to the "bg_free_blocks_count" filed in the group descriptors? Does the ext2/ext3 driver in the kernel maintains the relationship?