29 lines
1.1 KiB
ReStructuredText
29 lines
1.1 KiB
ReStructuredText
|
.. 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.
|