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

[Jason Wang <jasowang@redhat.com>]

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 <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.

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?

>
>> ---
>>
>> 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