netdev - Re: [PATCH net v4 3/4] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST

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Message-ID: <CACGkMEtxfZh=66TSTC2B8TdXWP-fsTrYFkfz5aOViYkZmmcvxg@mail.gmail.com>
Date: Mon, 10 Nov 2025 15:16:08 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org, 
	Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Heng Qi <hengqi@...ux.alibaba.com>, Willem de Bruijn <willemb@...gle.com>, 
	Jiri Pirko <jiri@...nulli.us>, Alvaro Karsz <alvaro.karsz@...id-run.com>, 
	virtualization@...ts.linux.dev
Subject: Re: [PATCH net v4 3/4] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN

On Mon, Nov 10, 2025 at 5:41 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Oct 30, 2025 at 10:53:01AM +0800, Jason Wang wrote:
> > On Wed, Oct 29, 2025 at 11:09 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > >
> > > The commit be50da3e9d4a ("net: virtio_net: implement exact header length
> > > guest feature") introduces support for the VIRTIO_NET_F_GUEST_HDRLEN
> > > feature in virtio-net.
> > >
> > > This feature requires virtio-net to set hdr_len to the actual header
> > > length of the packet when transmitting, the number of
> > > bytes from the start of the packet to the beginning of the
> > > transport-layer payload.
> > >
> > > However, in practice, hdr_len was being set using skb_headlen(skb),
> > > which is clearly incorrect. This commit fixes that issue.
> >
> > I still think it would be more safe to check the feature
>
> which feature VIRTIO_NET_F_GUEST_HDRLEN ?
>

Yes.

Thanks