From a44ad6835da52fdf4df2e482f45a167336555121 Mon Sep 17 00:00:00 2001 From: Harshad Shirwadkar Date: Thu, 5 Nov 2020 19:58:50 -0800 Subject: [PATCH] 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: Jan Kara Signed-off-by: Harshad Shirwadkar Reviewed-by: Jan Kara Link: https://lore.kernel.org/r/20201106035911.1942128-2-harshadshirwadkar@gmail.com Signed-off-by: Theodore Ts'o --- Documentation/filesystems/ext4/journal.rst | 6 ++++++ Documentation/filesystems/ext4/super.rst | 7 +++++++ fs/ext4/ext4.h | 7 +++++++ 3 files changed, 20 insertions(+) diff --git a/Documentation/filesystems/ext4/journal.rst b/Documentation/filesystems/ext4/journal.rst index 805a1e9ea3a5..849d5b119eb8 100644 --- a/Documentation/filesystems/ext4/journal.rst +++ b/Documentation/filesystems/ext4/journal.rst @@ -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: diff --git a/Documentation/filesystems/ext4/super.rst b/Documentation/filesystems/ext4/super.rst index 93e55d7c1d40..2eb1ab20498d 100644 --- a/Documentation/filesystems/ext4/super.rst +++ b/Documentation/filesystems/ext4/super.rst @@ -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: diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 45fcdbf538d1..d513553ceafa 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -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