Re: [Qemu-devel] [PATCH v2] net: Flush queued packets when guest resumes

[Fam Zheng <famz@redhat.com>]

On Tue, 07/07 12:19, Michael S. Tsirkin wrote:
> On Tue, Jul 07, 2015 at 05:09:09PM +0800, Fam Zheng wrote:
> > On Tue, 07/07 11:13, Michael S. Tsirkin wrote:
> > > On Tue, Jul 07, 2015 at 09:21:07AM +0800, Fam Zheng wrote:
> > > > Since commit 6e99c63 "net/socket: Drop net_socket_can_send" and friends,
> > > > net queues need to be explicitly flushed after qemu_can_send_packet()
> > > > returns false, because the netdev side will disable the polling of fd.
> > > > 
> > > > This fixes the case of "cont" after "stop" (or migration).
> > > > 
> > > > Signed-off-by: Fam Zheng <famz@redhat.com>
> > > 
> > > Note virtio has its own handler which must be used to
> > > flush packets - this one might run too early or too late.
> > 
> > Which handler do you mean? I don't think virtio-net handles resume now. (If it
> > does, we probably should drop it together with this change, since it's needed
> > by as all NICs.)
> > 
> > Fam
> 
> virtio_vmstate_change
> 
> It's all far from trivial. I suspect these whack-a-mole approach
> spreading purge here and there will only create more bugs.
> 
> Why would we ever need to process network packets when
> VM is not running? I don't see any point to it.
> How about we simply stop the job processing network on
> vm stop and restart on vm start?

I suppose it is too much for 2.4. I think this approach, adding
qemu_flush_queued_packets(), is consistent with its existing usage (when a
device is becoming active from inactive), like in e1000_write_config.

How about applying this and let's work on "stopping tap when VM not running"
for 2.5?

Fam