[RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute

[Darrick J. Wong]

On Tue, May 06, 2025 at 02:10:12PM +0200, Christoph Hellwig wrote:
> On Tue, May 06, 2025 at 07:25:06PM +0800, Zhang Yi wrote:
> > +       if (request_mask & STATX_WRITE_ZEROES_UNMAP &&
> > +           bdev_write_zeroes_unmap(bdev))
> > +               stat->result_mask |= STATX_WRITE_ZEROES_UNMAP;
> 
> That would be my expectation.  But then again this area seems to
> confuse me a lot, so maybe we'll get Christian or Dave to chim in.

Um... does STATX_WRITE_ZEROES_UNMAP protect a field somewhere?
It might be nice to expose the request alignment granularity/max
size/etc.  Or does this flag exist solely to support discovering that
FALLOC_FL_WRITE_ZEROES is supported?  In which case, why not discover
its existence by calling fallocate(fd, WRITE_ZEROES, 0, 0) like the
other modes?

--D