forked from Minki/linux
8a98ec7c7b
Move the ext4 data structures book to Documentation/filesystems/ext4/ since the administrative information moved elsewhere. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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.
|