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

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Message-ID: <CACGkMEuiyfH-QitiiKJ__-8NiTjoOfc8Nx5BwLM-GOfPpVEitA@mail.gmail.com>
Date: Mon, 13 Jan 2025 11:04:24 +0800
From: Jason Wang <jasowang@...hat.com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, 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 Fri, Jan 10, 2025 at 7:12 PM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>
> 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.
> >

So is this something that the driver should notice?

>
> 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.

I don't get this. We are talking about devices and we want to relax so
it should compatibile.

>
> 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.

I don't think we can fix it all.

Thanks

>