| Darrick J. Wong | 33dfadc | 2018-07-29 15:41:00 -0400 | [diff] [blame] | 1 | .. SPDX-License-Identifier: GPL-2.0 |
| 2 | |
| 3 | Block and inode Bitmaps |
| 4 | ----------------------- |
| 5 | |
| 6 | The data block bitmap tracks the usage of data blocks within the block |
| 7 | group. |
| 8 | |
| 9 | The inode bitmap records which entries in the inode table are in use. |
| 10 | |
| 11 | As with most bitmaps, one bit represents the usage status of one data |
| 12 | block or inode table entry. This implies a block group size of 8 \* |
| 13 | number\_of\_bytes\_in\_a\_logical\_block. |
| 14 | |
| 15 | NOTE: If ``BLOCK_UNINIT`` is set for a given block group, various parts |
| 16 | of the kernel and e2fsprogs code pretends that the block bitmap contains |
| 17 | zeros (i.e. all blocks in the group are free). However, it is not |
| 18 | necessarily the case that no blocks are in use -- if ``meta_bg`` is set, |
| 19 | the bitmaps and group descriptor live inside the group. Unfortunately, |
| 20 | ext2fs\_test\_block\_bitmap2() will return '0' for those locations, |
| 21 | which produces confusing debugfs output. |
| 22 | |
| 23 | Inode Table |
| 24 | ----------- |
| 25 | Inode tables are statically allocated at mkfs time. Each block group |
| 26 | descriptor points to the start of the table, and the superblock records |
| 27 | the number of inodes per group. See the section on inodes for more |
| 28 | information. |