[v7,0/8] block atomic writes for xfs

Message

John Garry Oct. 4, 2024, 9:22 a.m. UTC

This series expands atomic write support to filesystems, specifically
XFS.

Flag FS_XFLAG_ATOMICWRITES is added as an enabling flag for atomic writes.

XFS can be formatted for atomic writes as follows:
mkfs.xfs  -i atomicwrites=1 -b size=16384 /dev/sda

Support can be enabled through xfs_io command:
$xfs_io -c "chattr +W" filename
$xfs_io -c "lsattr -v" filename
[atomic-writes] filename
$xfs_io -c statx filename
...
stat.stx_atomic_write_unit_min = 16384
stat.stx_atomic_write_unit_max = 16384
stat.stx_atomic_write_segments_max = 1
...

Dependence on forcealign is gone for the moment. This means that we can
only write a single FS block atomically. Since we can now have FS block
size > PAGE_SIZE for XFS, we can write atomically write 4K+ blocks on
x86.

Using the large FS block size has downsides, so we still want the
forcealign feature.

Baseline is v6.12-rc1

Basic xfsprogs support at:
https://github.com/johnpgarry/xfsprogs-dev/tree/atomic-writes-v7

Patches for this series can be found at:
https://github.com/johnpgarry/linux/tree/atomic-writes-v6.12-fs-v7

Changes since v6:
- Add iomap documentation update (Darrick)
- Drop reflink restriction (Darrick, Christoph)
- Catch XFS buffered IO fallback (Darrick)
- Check IOCB_DIRECT in generic_atomic_write_valid()
- Tweaks to coding style (Darrick)
- Add RB tags from Darrick and Christoph (thanks!)

Changes since v5:
- Drop forcealign dependency
- Can support atomically writing a single FS block
- XFS_DIFLAG2_ATOMICWRITES is inherited from parent directories
- Add RB tags from Darrick (thanks!)

John Garry (8):
  block/fs: Pass an iocb to generic_atomic_write_valid()
  fs: Export generic_atomic_write_valid()
  fs/block: Check for IOCB_DIRECT in generic_atomic_write_valid()
  fs: iomap: Atomic write support
  xfs: Support FS_XFLAG_ATOMICWRITES
  xfs: Support atomic write for statx
  xfs: Validate atomic writes
  xfs: Support setting FMODE_CAN_ATOMIC_WRITE

 .../filesystems/iomap/operations.rst          | 11 ++++++
 block/fops.c                                  | 22 ++++++-----
 fs/iomap/direct-io.c                          | 38 +++++++++++++++++--
 fs/iomap/trace.h                              |  3 +-
 fs/read_write.c                               | 16 +++++---
 fs/xfs/libxfs/xfs_format.h                    | 11 +++++-
 fs/xfs/libxfs/xfs_inode_buf.c                 | 22 +++++++++++
 fs/xfs/libxfs/xfs_inode_util.c                |  6 +++
 fs/xfs/libxfs/xfs_sb.c                        |  2 +
 fs/xfs/xfs_buf.c                              |  7 ++++
 fs/xfs/xfs_buf.h                              |  3 ++
 fs/xfs/xfs_file.c                             | 10 +++++
 fs/xfs/xfs_inode.h                            | 22 +++++++++++
 fs/xfs/xfs_ioctl.c                            | 27 +++++++++++++
 fs/xfs/xfs_iops.c                             | 25 ++++++++++++
 fs/xfs/xfs_mount.h                            |  2 +
 fs/xfs/xfs_super.c                            |  4 ++
 include/linux/fs.h                            |  2 +-
 include/linux/iomap.h                         |  1 +
 include/uapi/linux/fs.h                       |  1 +
 20 files changed, 211 insertions(+), 24 deletions(-)