| .. SPDX-License-Identifier: GPL-2.0 | |
| 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. | |
| Inode Table | |
| ----------- | |
| Inode tables are statically allocated at mkfs time. Each block group | |
| descriptor points to the start of the table, and the superblock records | |
| the number of inodes per group. See the section on inodes for more | |
| information. |