netdev - Re: [PATCH v2 3/3] tun: Set num

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Message-ID: <2e015ee6-8a3b-43fb-b119-e1921139c74b@daynix.com>
Date: Fri, 10 Jan 2025 20:12:25 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>
Cc: Jonathan Corbet <corbet@....net>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, kvm@...r.kernel.org,
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org,
 Yuri Benditovich <yuri.benditovich@...nix.com>,
 Andrew Melnychenko <andrew@...nix.com>,
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com,
 devel@...nix.com
Subject: Re: [PATCH v2 3/3] tun: Set num_buffers for virtio 1.0

On 2025/01/10 19:23, Michael S. Tsirkin wrote:
> On Fri, Jan 10, 2025 at 11:27:13AM +0800, Jason Wang wrote:
>> On Thu, Jan 9, 2025 at 2:59 PM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>>>
>>> The specification says the device MUST set num_buffers to 1 if
>>> VIRTIO_NET_F_MRG_RXBUF has not been negotiated.
>>
>> Have we agreed on how to fix the spec or not?
>>
>> As I replied in the spec patch, if we just remove this "MUST", it
>> looks like we are all fine?
>>
>> Thanks
> 
> We should replace MUST with SHOULD but it is not all fine,
> ignoring SHOULD is a quality of implementation issue.
> 

Should we really replace it? It would mean that a driver conformant with 
the current specification may not be compatible with a device conformant 
with the future specification.

We are going to fix all implementations known to buggy (QEMU and Linux) 
anyway so I think it's just fine to leave that part of specification as is.