[RFC PATCH -next v3 07/10] fs: introduce FALLOC_FL_WRITE_ZEROES to fallocate

[Christoph Hellwig]

On Tue, Mar 18, 2025 at 03:35:42PM +0800, Zhang Yi wrote:
> Users can check the disk support of unmap write zeroes command by
> querying:
> 
>     /sys/block/<disk>/queue/write_zeroes_unmap

No, that is not in any way a good user interface.  Users need to be
able to query this on a per-file basis.

> Finally, this flag should not be specified in conjunction with the
> FALLOC_FL_KEEP_SIZE since allocating written extents beyond file EOF is
> not permitted, and filesystems that always require out-of-place writes
> should not support this flag since they still need to allocated new
> blocks during subsequent overwrites.

Should not or can't?  You're returning an error if this happens, so it
doesn't look like should is the right word here.