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From: Tao Lyu <tao.lyu@epfl.ch>
To: Christoph Hellwig <hch@infradead.org>
CC: Trond Myklebust <trondmy@hammerspace.com>, "linux-nfs@vger.kernel.org"
	<linux-nfs@vger.kernel.org>
Subject: Re: Question about O_APPEND | O_DIRECT
Thread-Topic: Question about O_APPEND | O_DIRECT
Thread-Index: AQHaHjflhODFfyeMXUSkxSGiPt/2HLCLuRkAgAKTcNCAAAYXgIAAEVQV
Date: Mon, 27 Nov 2023 16:41:17 +0000
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> On Mon, Nov 27, 2023 at 03:28:16PM +0000, Tao Lyu wrote:
>>=20
>> O_APPEND | O_DIRECT can be used to bypass the client cache for multiple =
threads writing data without caring of the orders (e.g., logs).
>>=20
>> Yes, to support O_APPEND | O_DIRECT, NFS must first support APPEND.
>> But the key point is that looks like NFS has supported O_APPEND already.
>> I can successfully open a file with "O_RDWR|O_APPEND".
>>=20
>> My confusion is why NFS supports O_RDWR and O_APPEND individually but do=
es not support this combination.

> Well, it does support O_RDWR|O_APPEND, just not with O_DIRECT?

Hi Christoph,=20

Yes, it just doesn't work 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.=A0 Not that
> we (Damien to be specific) plan to add support to Linux to also report
> the actual offset an O_APPEND write wrote to through io_uring as we
> have varios use cases for out of place write data stores for that.
> It would be great to also support that programming model over NFS.=