1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 Block and inode Bitmaps 3 Block and inode Bitmaps
4 ----------------------- 4 -----------------------
5 5
6 The data block bitmap tracks the usage of data 6 The data block bitmap tracks the usage of data blocks within the block
7 group. 7 group.
8 8
9 The inode bitmap records which entries in the 9 The inode bitmap records which entries in the inode table are in use.
10 10
11 As with most bitmaps, one bit represents the u 11 As with most bitmaps, one bit represents the usage status of one data
12 block or inode table entry. This implies a blo 12 block or inode table entry. This implies a block group size of 8 *
13 number_of_bytes_in_a_logical_block. 13 number_of_bytes_in_a_logical_block.
14 14
15 NOTE: If ``BLOCK_UNINIT`` is set for a given b 15 NOTE: If ``BLOCK_UNINIT`` is set for a given block group, various parts
16 of the kernel and e2fsprogs code pretends that 16 of the kernel and e2fsprogs code pretends that the block bitmap contains
17 zeros (i.e. all blocks in the group are free). 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 18 necessarily the case that no blocks are in use -- if ``meta_bg`` is set,
19 the bitmaps and group descriptor live inside t 19 the bitmaps and group descriptor live inside the group. Unfortunately,
20 ext2fs_test_block_bitmap2() will return '0' fo 20 ext2fs_test_block_bitmap2() will return '0' for those locations,
21 which produces confusing debugfs output. 21 which produces confusing debugfs output.
22 22
23 Inode Table 23 Inode Table
24 ----------- 24 -----------
25 Inode tables are statically allocated at mkfs 25 Inode tables are statically allocated at mkfs time. Each block group
26 descriptor points to the start of the table, a 26 descriptor points to the start of the table, and the superblock records
27 the number of inodes per group. See the secti 27 the number of inodes per group. See the section on inodes for more
28 information. 28 information.
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