Re: [PATCH v6 3/3] xfs: add support for FALLOC_FL_WRITE_ZEROES

On Thu, Jun 18, 2026 at 03:26:14PM +0200, Pankaj Raghav (Samsung) wrote:
> existing code **does not** overwrite any user data. Here is why:
> 
> - xfs_free_file_space (punch hole) punches inward (offset_ru -> end_rd)
>   and zeroes out from (offset -> offset_ru) and (end_rd -> end) with
>   xfs_zero_range

Ah, right.

> - Luckily, even though we consider offset_rd to end_ru in
>   alloc_file_space, XFS_BMAPI_ZERO will skip zeroing already written
>   edge blocks and only offset_ru -> end_rd are zeroed using unmap zero range.
>   ( (offset -> offset_ru) -> EXT_NORM, (offset_ru -> end_rd) -> HOLE,
>   (end_rd -> end) -> EXT_NORM)

Oh.  So this was lucky because of the corner cases.  I still think doing
the proper alignment in the higher level code and only calling down for
the area that we really want to zero would be benefitial here, if only
to make the code easier to follow.