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

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

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.

> ---
> 
> 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