mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-05 02:19:51 +00:00
ext4: import bitmaps chapter from wiki page
Import the chapter about bitmaps from the on-disk format wiki page into the kernel documentation. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
parent
3c6ba09dd3
commit
33dfadc747
2 changed files with 29 additions and 0 deletions
28
Documentation/filesystems/ext4/ondisk/bitmaps.rst
Normal file
28
Documentation/filesystems/ext4/ondisk/bitmaps.rst
Normal file
|
@ -0,0 +1,28 @@
|
|||
.. 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.
|
|
@ -8,3 +8,4 @@ have static metadata at fixed locations.
|
|||
|
||||
.. include:: super.rst
|
||||
.. include:: group_descr.rst
|
||||
.. include:: bitmaps.rst
|
||||
|
|
Loading…
Reference in a new issue