Re: [PATCH] NFSD: Implement FATTR4_CLONE_BLKSIZE attribute

[Christoph Hellwig <hch@infradead.org>]

On Tue, May 06, 2025 at 09:45:56AM -0400, Chuck Lever wrote:
> On 5/6/25 4:10 AM, Christoph Hellwig wrote:
> > On Sun, Apr 27, 2025 at 12:39:14PM -0400, cel@kernel.org wrote:
> >> NFSD can return 0 here, as at least one client implementation we
> >> are aware of (the Linux NFS client) treats 0 as meaning "CLONE has
> >> no alignment restrictions".
> > 
> > Usually clone does have a restriction, though.
> 
> Then should this patch extract that block size and report it? Pointer
> to sample code would kickstart me to get that done.

I think reporting 0 as unknown makes perfect sense, just don't claim
that there is no limitation.

The generic remap range checks for file system block size alignment:

	if (!IS_ALIGNED(pos_in, bs) || !IS_ALIGNED(pos_out, bs))
		return -EINVAL;

in generic_remap_checks.