Re: Question about O_APPEND | O_DIRECT

[Trond Myklebust <trondmy@hammerspace.com>]

On Tue, 2023-11-28 at 05:09 -0800, Christoph Hellwig wrote:
> On Mon, Nov 27, 2023 at 05:50:49PM -0800, Rick Macklem wrote:
> > > > Well, it does support O_RDWR|O_APPEND, just not with O_DIRECT?
> > > > 
> > > > Btw, I think an APPEND operation in NFS would be a very good
> > > > idea, and
> > > > I'd love to work with interested parties in the IETF on it.
> > It is not easy to deal with w.r.t. RPC retries.
> 
> Indeed.
> 
> > I suppose a NFSv4.2 extension that either requires (or strongly
> > recommends) persistent sessions might work?
> > (Persistent sessions should pretty well guarantee an RPC is not
> > redone on the server.)
> 
> I guess so.  That of course actually means we rely on a viable
> implementation of persistent sessions.  The Linux server doesn't
> support them, and I'm not sure which servers actually do.

Nobody is going to implement the overhead of persistent sessions just
in order to add support for APPEND.
The only thing that will be achieved by tying the functionality to
persistent sessions is to ensure that people will completely ignore the
spec.


-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com