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

On 6/18/2026 4:59 PM, Christoph Hellwig wrote:
> On Thu, Jun 18, 2026 at 11:22:45AM +0800, Zhang Yi wrote:
>> 1) if the two blocks straddling the boundaries have not yet been allocated,
>>    or allocated as unwritten, we should round outward the allocation range
>>    and zero out all allocated blocks, including those two boundary blocks.
>> 2) if the blocks at the boundaries are already in the written state — which
>>    can occur when we call FALLOC_FL_WRITE_ZEROES within the file size. We
>>    should be careful here: we should only zero the ranges [offset, offset_ru)
>>    and [end_rd, end) for the boundary blocks, leaving the already-written
>>    portions of the boundary blocks intact.
>>
>> Thoughs?
> 
> Yes.
> 
>> Regarding the second point, the current ext4 implementation has an issue —
>> it zeroes out the entire boundary blocks. I overlooked this previously, and
>> I appreciate you pointing it out.
> 
> Which means we're missing test coverage for this as well..
> 

Ha, I just re-checked the ext4 implementation and found that scenario 2 is
actually fine, Sorry I misread the code earlier. Fortunately, no data
corruption occurred. :-)

The real issue is in scenario 1, where the boundary blocks are not correctly
converted to written-type extents.

As for testing the unaligned case, I also agree that we should explicitly add
a dedicated test for it. Relying on existing fsstress and fsx is not reliable
enough in this regard.

Thanks,
Yi.