[PATCH v4 0/4] ext4: Add atomic writes support for DIO

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

v3 -> v4:
=========
1. Patch-1 changes the helper function from ext4_can_atomic_write() to
   ext4_inode_can_atomic_write() based on suggestions from Darrick and John.
   Patch-3 then goes and uses it.
2. Patch-4 adds an inline helper ext4_want_directio_fallback() which simplifies
   the logic checks and inherently fixes condition on when to return -ENOTBLK
   which otherwise was always returning true for any write or directio in
   ext4_iomap_end(). It was ok since ext4 only supports direct-io via iomap.
[v3]: https://lore.kernel.org/linux-xfs/cover.1730286164.git.ritesh.list@gmail.com/

(Note as mentioned below as well this is built on top of John XFS atomic series [2])
[2]: https://lore.kernel.org/linux-xfs/20241019125113.369994-1-john.g.garry@oracle.com/


v2 -> v3:
==========
1. Patch-1 adds an "experimental" string in dmesg log during mount when EXT4
   detects that it is capable of doing DIO atomic writes on a given device
   with min and max unit details.
2. Patch-4 has been updated to avoid returning -ENOTBLK (in ext4_iomap_end)
   if the request belongs to atomic write. This patch also adds a WARN_ON_ONCE()
   if atomic write ever fallback to buffered-io (to catch any unwanted bugs in the future).
   More details in the commit log of patch-4.
3. Collected RBs tag from John for Patch 2 & 3.

[v2]: https://lore.kernel.org/linux-ext4/cover.1729944406.git.ritesh.list@gmail.com/

Previous cover letter log:

In v2, we had split the series and this one only takes care of
atomic writes for single fsblock.
That means for now this gets only enabled on bs < ps systems on ext4.
Enablement of atomic writes for bigalloc (multi-fsblock support) is still
under discussion and may require general consensus within the filesystem
community [1].

This series adds the base feature support to enable atomic writes in
direct-io path for ext4. We advertise the minimum and the maximum atomic
write unit sizes via statx on a regular file.

This series allows users to utilize atomic write support using -
1. on bs < ps systems via - mkfs.ext4 -F -b 16384 /dev/sda

This can then be utilized using -
	xfs_io -fdc "pwrite -V 1 -A -b16k 0 16k" /mnt/f1

This is built on top of John's DIO atomic write series for XFS [2].
The VFS and block layer enablement for atomic writes were merged already.


[1]: https://lore.kernel.org/linux-ext4/87jzdvmqfz.fsf@gmail.com
[2]: https://lore.kernel.org/linux-xfs/20241019125113.369994-1-john.g.garry@oracle.com/


Changelogs:
===========
PATCH -> PATCH v2:
- addressed review comments from John and Darrick.
- renamed ext4_sb_info variables names: fs_awu* -> s_awu*
- [PATCH]: https://lore.kernel.org/linux-ext4/cover.1729825985.git.ritesh.list@gmail.com/

RFC -> PATCH:
- Dropped RFC tag
- Last RFC was posted a while ago but back then a lot of VFS and block layer
  interfaces were still not merged. Those are now merged, thanks to John and
  everyone else.
- [RFC] - https://lore.kernel.org/linux-ext4/cover.1709356594.git.ritesh.list@gmail.com/


Ritesh Harjani (IBM) (4):
  ext4: Add statx support for atomic writes
  ext4: Check for atomic writes support in write iter
  ext4: Support setting FMODE_CAN_ATOMIC_WRITE
  ext4: Do not fallback to buffered-io for DIO atomic write

 fs/ext4/ext4.h  | 10 ++++++++++
 fs/ext4/file.c  | 24 ++++++++++++++++++++++++
 fs/ext4/inode.c | 39 ++++++++++++++++++++++++++++++++++-----
 fs/ext4/super.c | 31 +++++++++++++++++++++++++++++++
 4 files changed, 99 insertions(+), 5 deletions(-)

--
2.46.0