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Date: Wed, 3 Apr 2013 14:25:15 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2 V3] virtio-spec: dynamic network
 offloads configuration
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To: Rusty Russell <rusty@rustcorp.com.au>
Cc: qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Yan Vugenfirer <yan@daynix.com>, Ronen Hod <rhod@redhat.com>, Dmitry Fleytman <dmitry@daynix.com>, Dmitry Fleytman <dfleytma@redhat.com>

On Wed, Apr 03, 2013 at 11:50:19AM +1030, Rusty Russell wrote:
> Dmitry Fleytman <dmitry@daynix.com> writes:
> > From: Dmitry Fleytman <dfleytma@redhat.com>
> >
> > Virtio-net driver currently negotiates network offloads
> > on startup via features mechanism and have no ability to
> > change offloads state later.
> > This patch introduced a new control command that allows
> > to configure device network offloads state dynamically.
> > The patch also introduces a new feature flag
> > VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.
> >
> > Signed-off-by: Dmitry Fleytman <dfleytma@redhat.com>
> 
> (BTW, I like to be CC'd on these things directly, so I don't miss them)
> 
> The idea is fine.
> 
> But I dislike the duplication of constants: let's just use the feature
> bits directly:
> 
> #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/ partial csum */
> #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in. */
> #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in. */
> #define VIRTIO_NET_F_GUEST_ECN	9	/* Guest can handle TSO[6] w/ ECN in. */
> #define VIRTIO_NET_F_GUEST_UFO	10	/* Guest can handle UFO in. */
> 
> You want this, because you have to test against them anyway before
> trying to re-enable them.
> 
> And secondly, it'll be much clearer if you don't say "change" but
> "disable and re-enable", which is what's actually allowed.
> 
> Thanks,
> Rusty.

Okay and let's make command it bigger, say 64 bit then,
in case we add lots of feature bits in the future?