xfs: add support for FALLOC_FL_WRITE_ZEROES

If the underlying block device supports the unmap write zeroes
operation, this flag allows users to quickly preallocate a file with
written extents that contain zeroes. This is beneficial for subsequent
overwrites as it prevents the need for unwritten-to-written extent
conversions, thereby significantly reducing metadata updates and journal
I/O overhead, improving overwrite performance.

Punch the range first so it becomes a hole, update the size via
xfs_falloc_setsize() while it is still a hole (so its xfs_zero_range()
skips it and avoids rezeroing), then convert it to written
zeroed extents. A crash between the size update and the conversion is
safe, as a hole within i_size reads back as zeroes.

Co-developed-by: Lukas Herbolt <lukas@herbolt.com>
Signed-off-by: Lukas Herbolt <lukas@herbolt.com>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

0 files changed, 0 insertions, 0 deletions