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

[Michael S. Tsirkin]

On Tue, Jul 07, 2015 at 04:58:29PM +0800, Jason Wang wrote:
> 
> 
> On 07/07/2015 04:13 PM, 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 <address@hidden>
> > Note virtio has its own handler which must be used to
> > flush packets - this one might run too early or too late.
> 
> If runs too realy (DRIVER_OK is not set), then: packet will be dropped
> (if this patch is used with "drop virtio_net_can_receive()", or the
> queue will be purged since qemu_can_send_packet() returns false. If too
> late, at least tap read poll will be enabled. So still looks ok?

It's still not helpful for virtio. So which cards are fixed?

I just find the comment
        This fixes the case of "cont" after "stop" (or migration)
too vague.
Can you please include the info about what's broken in the commit log?

> >
> >> ---
> >>
> >> 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);
> >>          }
> >>      }
> >> -- 
> >> 2.4.3