Re: Question about O_APPEND | O_DIRECT

[Tao Lyu <tao.lyu@epfl.ch>]

> On Mon, Nov 27, 2023 at 03:28:16PM +0000, Tao Lyu wrote:
>> 
>> 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).
>> 
>> 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".
>> 
>> My confusion is why NFS supports O_RDWR and O_APPEND individually but does not support this combination.

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

Hi Christoph, 

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.  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.