Re: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice

Shirley Ma
2011-05-19T19:42:49Z

On Wed, 2011-05-18 at 10:00 -0700, Shirley Ma wrote:
> On Wed, 2011-05-18 at 19:51 +0300, Michael S. Tsirkin wrote:
> > > > Yes, I agree. I think for tcpdump, we really need to copy the
> > data
> > > > anyway, to avoid guest changing it in between. So we do that
> and
> > then
> > > > use the copy everywhere, release the old one. Hmm?
> > >
> > > Yes. Old one use zerocopy, new one use copy data.
> > >
> > > Thanks
> > > Shirley
> >
> > No, that's wrong, as they might become different with a
> > malicious guest. As long as we copied already, lets realease
> > the data and have everyone use the copy.
>
> Ok, I will patch pskb_expand_head to test it out.

I am patching skb_copy, skb_clone, pskb_copy, pskb_expand_head to
convert a zero-copy skb to a copy skb to avoid this kind of issue.

This overhead won't impact macvtap/vhost TX zero-copy normally.

Shirley