Re: [Qemu-devel] [PATCH] net: prevent sending packets while guest is stopped

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Sep 04, 2014 at 12:55:38PM +0800, Jason Wang wrote:
> On 09/02/2014 10:23 PM, Stefan Hajnoczi wrote:
> > Do not modify guest memory or devices when the guest is stopped.
> > Currently the netdevs still send packets while the guest is stopped if
> > their file descriptor was being monitored for write (e.g. the socket
> > write buffer filled before the guest was stopped).
> >
> > Netdevs call qemu_flush_queued_packets() when the file descriptor
> > becomes writable again.  Don't resume packet processing when this
> > happens.
> >
> > Instead we flush queues when the guest resumes.
> >
> > Cc: qemu-stable@nongnu.org
> > Reported-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> > Note this fixes the transmit side.  The receive side was recently fixed in
> > "net: Forbid dealing with packets when VM is not running".
> >
> >  net/net.c | 30 ++++++++++++++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >
> > diff --git a/net/net.c b/net/net.c
> > index 6d930ea..74ec07a 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -47,6 +47,7 @@
> >  # define CONFIG_NET_BRIDGE
> >  #endif
> >  
> > +static VMChangeStateEntry *net_change_state_entry;
> >  static QTAILQ_HEAD(, NetClientState) net_clients;
> >  
> >  const char *host_net_devices[] = {
> > @@ -506,6 +507,11 @@ void qemu_purge_queued_packets(NetClientState *nc)
> >  
> >  void qemu_flush_queued_packets(NetClientState *nc)
> >  {
> > +    /* Guest memory and devices must not be modified while stopped */
> > +    if (!runstate_is_running()) {
> > +        return;
> > +    }
> > +
> 
> Consider migration case, this will prevent
> sent_cb(virtio_net_tx_complete) from being called at source. Since we
> don't migrate queue and async_tx. This may lead a interrupt lost in
> destination after migration?
> 
> (Looks like virtio_net is the only user that uses async sending, not
> sure why this is needed)

Good point, I noticed this too.
Sorry about missing this the first time around.