Re: [Qemu-devel] [PATCH] e1000/rtl8139: forbid dealing with packets when VM is paused

[Stefan Hajnoczi]

On Wed, May 14, 2014 at 03:46:48PM +0300, Michael S. Tsirkin wrote:
> On Wed, May 14, 2014 at 02:30:26PM +0200, Stefan Hajnoczi wrote:
> > On Thu, May 08, 2014 at 12:51:05PM +0000, Zhanghailiang wrote:
> > > > If you implement this in the net layer then that problem is easy to 
> > > > resolve since
> > > > we can flush all queues when the guest resumes to get packets flowing 
> > > > again.
> > > > 
> > > Do you mean we should also listen for VM runstate changes in net layer, 
> > > and when detect runstate changes back to running , we flush all queues 
> > > actively? Am I misunderstanding? 
> > > Or we can do it *before* qemu (exactly when it check if it can send 
> > > packets) send packets to guest again, this way will be simple, but it 
> > > also need know the change of runstate. Any idea? 
> > 
> > When the runstate changes back to running, we definitely need to flush
> > queues to get packets flowing again.  I think the simplest way of doing
> > that is in the net layer so individual NICs and netdevs don't have to
> > duplicate this code.
> > 
> > Stefan
> 
> That will help with networking but not other devices.
> The issue isn't limited to networking at all.
> How about we stop all io threads with the vm?
> 
> That will address the issue in a generic way.

I'm not sure if it works in all cases, for example iSCSI where we send
nop keepalives.

Stefan