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Date: Tue, 28 Nov 2023 05:09:05 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Rick Macklem <rick.macklem@gmail.com>
Cc: Chuck Lever III <chuck.lever@oracle.com>,
	Christoph Hellwig <hch@infradead.org>, Tao Lyu <tao.lyu@epfl.ch>,
	Trond Myklebust <trondmy@hammerspace.com>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: Question about O_APPEND | O_DIRECT
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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.