Re: [LSF/MM/BPF TOPIC] Implementing the NFS v4.2 WRITE_SAME operation: VFS or NFS ioctl() ?

[Matthew Wilcox <willy@infradead.org>]

On Tue, Jan 14, 2025 at 04:38:03PM -0500, Anna Schumaker wrote:
> I've seen a few requests for implementing the NFS v4.2 WRITE_SAME [1] operation over the last few months [2][3] to accelerate writing patterns of data on the server, so it's been in the back of my mind for a future project. I'll need to write some code somewhere so NFS & NFSD can handle this request. I could keep any implementation internal to NFS / NFSD, but I'd like to find out if local filesystems would find this sort of feature useful and if I should put it in the VFS instead.

I think we need more information.  I read over the [2] and [3] threads
and the spec.  It _seems like_ the intent in the spec is to expose the
underlying SCSI WRITE SAME command over NFS, but at least one other
response in this thread has been to design an all-singing, all-dancing
superset that can write arbitrary sized blocks to arbitrary locations
in every file on every filesystem, and I think we're going to design
ourselves into an awful implementation if we do that.

Can we confirm with the people who actually want to use this that all
they really want is to be able to do WRITE SAME as if they were on a
local disc, and then we can implement that in a matter of weeks instead
of taking a trip via Uranus.