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

[Fam Zheng <famz@redhat.com>]

On Tue, 07/07 15:44, Jason Wang wrote:
> 
> 
> On 07/07/2015 09:21 AM, 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>
> >
> > ---
> >
> > v2: Unify with VM stop handler. (Stefan)
> > ---
> >  net/net.c | 19 ++++++++++++-------
> >  1 file changed, 12 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/net.c b/net/net.c
> > index 6ff7fec..28a5597 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -1257,14 +1257,19 @@ void qmp_set_link(const char *name, bool up, Error **errp)
> >  static void net_vm_change_state_handler(void *opaque, int running,
> >                                          RunState state)
> >  {
> > -    /* Complete all queued packets, to guarantee we don't modify
> > -     * state later when VM is not running.
> > -     */
> > -    if (!running) {
> > -        NetClientState *nc;
> > -        NetClientState *tmp;
> > +    NetClientState *nc;
> > +    NetClientState *tmp;
> >  
> > -        QTAILQ_FOREACH_SAFE(nc, &net_clients, next, tmp) {
> > +    QTAILQ_FOREACH_SAFE(nc, &net_clients, next, tmp) {
> > +        if (running) {
> > +            /* Flush queued packets and wake up backends. */
> > +            if (nc->peer && qemu_can_send_packet(nc)) {
> > +                qemu_flush_queued_packets(nc->peer);
> > +            }
> > +        } else {
> > +            /* Complete all queued packets, to guarantee we don't modify
> > +             * state later when VM is not running.
> > +             */
> >              qemu_flush_or_purge_queued_packets(nc, true);
> >          }
> 
> Looks like qemu_can_send_packet() checks both nc->peer and runstate. So
> probably, we can simplify this to:
> 
> if (qemu_can_send_packet(nc))
>     qemu_flush_queued_packets(nc->peer);
> else
>     qemu_flush_or_purge_queued_packets(nc, true);
> 
> >      }
> 

qemu_can_send_packet returns 1 if !nc->peer, so this doesn't work.

Fam