| .. 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. |
