netdev - Re: dhclient, checksum and tap

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Message-ID: <20100627082439.GA8472@redhat.com>
Date:	Sun, 27 Jun 2010 11:24:40 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	herbert.xu@...hat.com, netdev@...r.kernel.org
Subject: Re: dhclient, checksum and tap

On Sat, Jun 26, 2010 at 08:03:20PM -0700, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@...hat.com>
> Date: Sun, 27 Jun 2010 00:14:19 +0300
> 
> > On Fri, Jun 25, 2010 at 11:21:52AM -0700, David Miller wrote:
> >> We added the af_packet status as the migration path to deal with
> >> this issue in the cleanest manner possible.  Putting a new hack
> >> into the TAP driver works contrary to that goal.
> > 
> > Hmm, problem is, using the af_packets status requires
> > userspace changes, and so does not help old clients.
> > And for virt, clients might be running old kernels without this support.
> > qemu has a hack to make old guests running within qemu work.
> > I guess I can copy that hack into vhost - a bit ugly as I don't have
> > access to the original skb there, so I will have to duplcate some logic,
> > but doable.  Is this what you suggest?  OTOH if we had the workaround in
> > tap, this could replace hacks in both vhost and qemu.
> 
> If you add the TAP thing you can _never_ remove it.  Exactly for the
> same reason that the qemu thing can never be removed.  It'll always be
> needed for the sake of old guests running old stuff.
> 
> This is why I truly believe that keeping the af_packet status thing as
> the only kernel side assist is likely best in the long run.

Just to spell it out for me, you think the hack should be done
in vhost-net?

-- 
MST
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