Commit a44ad683 authored by Harshad Shirwadkar's avatar Harshad Shirwadkar Committed by Theodore Ts'o
Browse files

ext4: describe fast_commit feature flags 



Fast commit feature has flags in the file system as well in JBD2. The
meaning of fast commit feature flags can get confusing. Update docs
and code to add more documentation about it.

Suggested-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20201106035911.1942128-2-harshadshirwadkar@gmail.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 7067b261

Documentation/filesystems/ext4/journal.rst

+6 −0
Original line number Diff line number Diff line
@@ -256,6 +256,10 @@ which is 1024 bytes long: 
     - s\_padding2

     -

   * - 0x54

     - \_\_be32

     - s\_num\_fc\_blocks

     - Number of fast commit blocks in the journal.

   * - 0x58

     - \_\_u32

     - s\_padding[42]

     -
@@ -310,6 +314,8 @@ The journal incompat features are any combination of the following: 
     - This journal uses v3 of the checksum on-disk format. This is the same as

       v2, but the journal block tag size is fixed regardless of the size of

       block numbers. (JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3)

   * - 0x20

     - Journal has fast commit blocks. (JBD2\_FEATURE\_INCOMPAT\_FAST\_COMMIT)



.. _jbd2_checksum_type:

Documentation/filesystems/ext4/super.rst

+7 −0
Original line number Diff line number Diff line
@@ -596,6 +596,13 @@ following: 
     - Sparse Super Block, v2. If this flag is set, the SB field s\_backup\_bgs

       points to the two block groups that contain backup superblocks

       (COMPAT\_SPARSE\_SUPER2).

   * - 0x400

     - Fast commits supported. Although fast commits blocks are

       backward incompatible, fast commit blocks are not always

       present in the journal. If fast commit blocks are present in

       the journal, JBD2 incompat feature

       (JBD2\_FEATURE\_INCOMPAT\_FAST\_COMMIT) gets

       set (COMPAT\_FAST\_COMMIT).



.. _super_incompat:

fs/ext4/ext4.h

+7 −0
Original line number Diff line number Diff line
@@ -1863,6 +1863,13 @@ static inline bool ext4_verity_in_progress(struct inode *inode) 
#define EXT4_FEATURE_COMPAT_RESIZE_INODE	0x0010

#define EXT4_FEATURE_COMPAT_DIR_INDEX		0x0020

#define EXT4_FEATURE_COMPAT_SPARSE_SUPER2	0x0200

/*

 * The reason why "FAST_COMMIT" is a compat feature is that, FS becomes

 * incompatible only if fast commit blocks are present in the FS. Since we

 * clear the journal (and thus the fast commit blocks), we don't mark FS as

 * incompatible. We also have a JBD2 incompat feature, which gets set when

 * there are fast commit blocks present in the journal.

 */

#define EXT4_FEATURE_COMPAT_FAST_COMMIT		0x0400

#define EXT4_FEATURE_COMPAT_STABLE_INODES	0x0800