netdev - Re: [PATCH] virtio: don't set VIRTIO_NET_HDR_F_DATA

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Date:   Fri, 20 Jan 2017 00:30:01 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Rolf Neugebauer <rolf.neugebauer@...ker.com>,
        netdev@...r.kernel.org, davem@...emloft.net,
        rppt@...ux.vnet.ibm.com
Subject: Re: [PATCH] virtio: don't set VIRTIO_NET_HDR_F_DATA_VALID on xmit

On Thu, Jan 19, 2017 at 11:06:59AM +0800, Jason Wang wrote:
> 
> 
> On 2017年01月18日 23:18, Michael S. Tsirkin wrote:
> > On Wed, Jan 18, 2017 at 11:54:21AM +0800, Jason Wang wrote:
> > > On 2017年01月18日 02:27, Michael S. Tsirkin wrote:
> > > > On Tue, Jan 17, 2017 at 06:13:51PM +0000, Rolf Neugebauer wrote:
> > > > > This patch part reverts fd2a0437dc33 and e858fae2b0b8 which introduced a
> > > > > subtle change in how the virtio_net flags are derived from the SKBs
> > > > > ip_summed field.
> > > > > 
> > > > > With the above commits, the flags are set to VIRTIO_NET_HDR_F_DATA_VALID
> > > > > when ip_summed == CHECKSUM_UNNECESSARY, thus treating it differently to
> > > > > ip_summed == CHECKSUM_NONE, which should be the same.
> > > > > 
> > > > > Further, the virtio spec 1.0 / CS04 explicitly says that
> > > > > VIRTIO_NET_HDR_F_DATA_VALID must not be set by the driver.
> > > > > 
> > > > > Signed-off-by: Rolf Neugebauer<rolf.neugebauer@...ker.com>
> > > > Fixes: fd2a0437dc33 ("virtio_net: introduce virtio_net_hdr_{from,to}_skb")
> > > > Fixes: e858fae2b0b8 (" virtio_net: use common code for virtio_net_hdr and skb GSO conversion")
> > > > Acked-by: Michael S. Tsirkin<mst@...hat.com>
> > > > 
> > > > Should be backported into stable as well.
> > > Looks like a side effect is that we will never see this on receive path?
> > I thought receive path is using virtio_net_hdr_to_skb - isn't it?
> > 
> 
> The problem is tun use this on xmit.
> 
> Thanks

Oh I missed that. I agree, let's add a flag that allows this.

-- 
MST