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 32f6987f9384 (xfs/for-next) Merge branch 'xfs-6.15-merge' into for-next [0] https://lore.kernel.org/linux-xfs/20250102140411.14617-1-john.g.garry@xxxxxxxxxx/ Differences to v4: - Omit iomap patches which have already been queued - Add () in xfs_bmap_compute_alignments() (Dave) - Rename awu_max -> m_awu_max (Carlos) - Add RFC to change IOMAP flag names - Rebase Differences to v3: - Error !reflink in xfs_atomic_write_sw_iomap_begin() (Darrick) - Fix unused variable (kbuild bot) - Add RB tags from Darrick (Thanks!) 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!) John Garry (10): xfs: Pass flags to xfs_reflink_allocate_cow() xfs: Switch atomic write size check in xfs_file_write_iter() xfs: Refactor xfs_reflink_end_cow_extent() 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 iomap: Rename ATOMIC flags again .../filesystems/iomap/operations.rst | 6 +- fs/ext4/inode.c | 2 +- fs/iomap/direct-io.c | 18 +-- fs/iomap/trace.h | 3 +- fs/xfs/libxfs/xfs_bmap.c | 4 + fs/xfs/libxfs/xfs_bmap.h | 6 +- fs/xfs/xfs_file.c | 61 +++++++- fs/xfs/xfs_iomap.c | 144 ++++++++++++++++- fs/xfs/xfs_iomap.h | 1 + fs/xfs/xfs_iops.c | 32 +++- 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 | 10 +- 16 files changed, 400 insertions(+), 74 deletions(-) -- 2.31.1
