Re: [PATCH v1 05/18] xprtrdma: Avoid using Write list for small NFS READ requests

Chuck Lever
2016-04-12T18:08:25Z

> On Apr 12, 2016, at 1:01 PM, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote:
>
> On Tue, Apr 12, 2016 at 10:49:24AM -0400, Chuck Lever wrote:
>>>> No, pre-4.2 Linux servers have a bug that can be fixed by
>>>> applying the above commit, which shouldn't be difficult to
>>>> backport.
>>>>
>>>> Clients have always been allowed to send NFS READ this way.
>>>
>>> But the clients might be out in a the wild. I think we'll need at
>>> least a mount option to work around them.
>>
>> Huh?
>>
>> I'm talking about non-Linux clients. RFC 5666 allows
>> this behavior, it always has. The Linux server before
>> 9d11b51ce7c1 is broken, full stop.
>
> You are deliverately breaking exsisting and fairly recent clients.

How am I breaking existing clients? Before 4.7, our
client works with a broken Linux NFS server and it
works with a fixed one.

_New_ clients won't work with broken servers.

> I see why we want to do this, but there needs to be an options
> that things keep working. The idea of upgrading your client from
> 4.6 to 4.7 and NFS simply not working anymore with the developer
> knowing it and not providing a workaround is simply not an option.

I don't understand why this approach was reasonable in
the past, but is now suddenly not workable.

We have a workaround: Use NFS/TCP on IPoIB.

--
Chuck Lever

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