Currently atomic write support for xfs is limited to writing a single block as we have no way to guarantee alignment and that the write covers a single extent. This series introduces a method to issue atomic writes via a software emulated method. The software emulated method is used as a fallback for when attempting to issue an atomic write over misaligned or multiple extents. For XFS, this support is based on CoW. The basic idea of this CoW method is to alloc a range in the CoW fork, write the data, and atomically update the mapping. Initial mysql performance testing has shown this method to perform ok. However, there we are only using 16K atomic writes (and 4K block size), so typically - and thankfully - this software fallback method won't be used often. For other FSes which want large atomics writes and don't support CoW, I think that they can follow the example in [0]. Based on 2d873efd174b (tag: xfs-fixes-6.14-rc4) xfs: flush inodegc before swapon [0] https://lore.kernel.org/linux-xfs/20250102140411.14617-1-john.g.garry@xxxxxxxxxx/ Differences to v2: (all from Darrick) - Add dedicated function for xfs iomap sw-based atomic write - Don't ignore xfs_reflink_end_atomic_cow() -> xfs_trans_commit() return value - Pass flags for reflink alloc functions - Rename IOMAP_ATOMIC_COW -> IOMAP_ATOMIC_SW - Coding style corrections and comment improvements - Add RB tags (thanks!) Differences to RFC: - Rework CoW alloc method - Rename IOMAP_ATOMIC -> IOMAP_ATOMIC_HW - Rework transaction commit func args - Chaneg resblks size for transaction commit - Rename BMAPI extszhint align flag John Garry (11): xfs: Pass flags to xfs_reflink_allocate_cow() iomap: Rename IOMAP_ATOMIC -> IOMAP_ATOMIC_HW xfs: Switch atomic write size check in xfs_file_write_iter() xfs: Refactor xfs_reflink_end_cow_extent() iomap: Support SW-based atomic writes xfs: Reflink CoW-based atomic write support xfs: Iomap SW-based atomic write support xfs: Add xfs_file_dio_write_atomic() xfs: Commit CoW-based atomic writes atomically xfs: Update atomic write max size xfs: Allow block allocator to take an alignment hint Ritesh Harjani (IBM) (1): iomap: Lift blocksize restriction on atomic writes .../filesystems/iomap/operations.rst | 20 ++- fs/ext4/inode.c | 2 +- fs/iomap/direct-io.c | 20 +-- fs/iomap/trace.h | 2 +- fs/xfs/libxfs/xfs_bmap.c | 7 +- fs/xfs/libxfs/xfs_bmap.h | 6 +- fs/xfs/xfs_file.c | 59 ++++++- fs/xfs/xfs_iomap.c | 150 +++++++++++++++++- fs/xfs/xfs_iomap.h | 1 + fs/xfs/xfs_iops.c | 31 +++- fs/xfs/xfs_iops.h | 2 + fs/xfs/xfs_mount.c | 28 ++++ fs/xfs/xfs_mount.h | 1 + fs/xfs/xfs_reflink.c | 145 ++++++++++++----- fs/xfs/xfs_reflink.h | 11 +- include/linux/iomap.h | 8 +- 16 files changed, 421 insertions(+), 72 deletions(-) -- 2.31.1
