Re: [Qemu-devel] [PATCH V2] net: Fix dealing with packets when runstate changes

[zhanghailiang <zhang.zhanghailiang@huawei.com>]

On 2014/8/22 15:40, Jason Wang wrote:
> On 08/21/2014 08:39 PM, zhanghailiang wrote:
>> For all NICs(except virtio-net) emulated by qemu,
>> Such as e1000, rtl8139, pcnet and ne2k_pci,
>> Qemu can still receive packets when VM is not running.
>> If this happened in *migration's* last PAUSE VM stage,
>> The new dirty RAM related to the packets will be missed,
>> And this will lead serious network fault in VM.
>>
>> To avoid this, we forbid receiving packets in generic net code when
>> VM is not running. Also, when the runstate changes back to running,
>> we definitely need to flush queues to get packets flowing again.
> Hi:
>
> Can you describe what will happen if you don't flush queues after vm is
> started? Btw, the notifier dependency and impact on vhost should be
> mentioned here as well.

Hi Jason,

There is no side-effect for vhost-net because in nic_vmstate_change_handler callback,
We will check the return value of nc->info->can_receive before flush queues,
If the vhost-net(virtio-net) is not ready, it will return 0, then we will not
do the flush action.

Also i have tested this patch with vhost_net, include when multiqueue is on,
Everything seems to be Ok!

When nc->info->receive return 0, the receive_disabled will be set to 1,
If this happened just before VM pause(is not running), after VM runstate
change back to run, the receive_disabled is still 1, if qemu want to
send packets to VM, it will always fail until something happen to clear it.
So we'd better to clear it after runstate change back to run.

>>
>> Here we implement this in the net layer:
>> (1) Judge the vm runstate in qemu_can_send_packet
>> (2) Add a member 'VMChangeStateEntry *vmstate' to struct NICState,
>> Which will listen for VM runstate changes.
>> (3) Register a handler function for VMstate change.
>> When vm changes back to running, we flush all queues in the callback function.
>> (4) Remove checking vm state in virtio_net_can_receive
>>
>> Signed-off-by: zhanghailiang<zhang.zhanghailiang@huawei.com>
>> ---
>> v2:
>> - remove the superfluous check of nc->received_disabled
>> ---
>>   hw/net/virtio-net.c |  4 ----
>>   include/net/net.h   |  2 ++
>>   net/net.c           | 31 +++++++++++++++++++++++++++++++
>>   3 files changed, 33 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 268eff9..287d762 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -839,10 +839,6 @@ static int virtio_net_can_receive(NetClientState *nc)
>>       VirtIODevice *vdev = VIRTIO_DEVICE(n);
>>       VirtIONetQueue *q = virtio_net_get_subqueue(nc);
>>
>> -    if (!vdev->vm_running) {
>> -        return 0;
>> -    }
>> -
>>       if (nc->queue_index>= n->curr_queues) {
>>           return 0;
>>       }
>> diff --git a/include/net/net.h b/include/net/net.h
>> index ed594f9..a294277 100644
>> --- a/include/net/net.h
>> +++ b/include/net/net.h
>> @@ -8,6 +8,7 @@
>>   #include "net/queue.h"
>>   #include "migration/vmstate.h"
>>   #include "qapi-types.h"
>> +#include "sysemu/sysemu.h"
>>
>>   #define MAX_QUEUE_NUM 1024
>>
>> @@ -96,6 +97,7 @@ typedef struct NICState {
>>       NICConf *conf;
>>       void *opaque;
>>       bool peer_deleted;
>> +    VMChangeStateEntry *vmstate;
>>   } NICState;
>>
>>   NetClientState *qemu_find_netdev(const char *id);
>> diff --git a/net/net.c b/net/net.c
>> index 6d930ea..113a37b 100644
>> --- a/net/net.c
>> +++ b/net/net.c
>> @@ -242,6 +242,28 @@ NetClientState *qemu_new_net_client(NetClientInfo *info,
>>       return nc;
>>   }
>>
>> +static void nic_vmstate_change_handler(void *opaque,
>> +                                       int running,
>> +                                       RunState state)
>> +{
>> +    NICState *nic = opaque;
>> +    NetClientState *nc;
>> +    int i, queues;
>> +
>> +    if (!running) {
>> +        return;
>> +    }
>> +
>> +    queues = MAX(1, nic->conf->peers.queues);
>> +    for (i = 0; i<  queues; i++) {
>> +        nc =&nic->ncs[i];
>> +        if (nc->info->can_receive&&  !nc->info->can_receive(nc)) {
>> +            continue;
>> +        }
>
> Why not just using qemu_can_send_packet() here?

qemu_can_send_packet will check the value of receive_disabled,
Our purpose is to clear it, if its value is 1.

May be we should check it as follow:

      if ((!nc->receive_disabled) || (nc->info->can_receive && !nc->info->can_receive(nc)) {
          continue;
       }
       qemu_flush_queued_packets(nc);



>> +        qemu_flush_queued_packets(nc);
>> +    }
>> +}
>> +
>>   NICState *qemu_new_nic(NetClientInfo *info,
>>                          NICConf *conf,
>>                          const char *model,
>> @@ -259,6 +281,8 @@ NICState *qemu_new_nic(NetClientInfo *info,
>>       nic->ncs = (void *)nic + info->size;
>>       nic->conf = conf;
>>       nic->opaque = opaque;
>> +    nic->vmstate = qemu_add_vm_change_state_handler(nic_vmstate_change_handler,
>> +                                                    nic);
>>
>>       for (i = 0; i<  queues; i++) {
>>           qemu_net_client_setup(&nic->ncs[i], info, peers[i], model, name,
>> @@ -379,6 +403,7 @@ void qemu_del_nic(NICState *nic)
>>           qemu_free_net_client(nc);
>>       }
>>
>> +    qemu_del_vm_change_state_handler(nic->vmstate);
>>       g_free(nic);
>>   }
>>
>> @@ -452,6 +477,12 @@ void qemu_set_vnet_hdr_len(NetClientState *nc, int len)
>>
>>   int qemu_can_send_packet(NetClientState *sender)
>>   {
>> +    int vmstat = runstate_is_running();
>> +
>> +    if (!vmstat) {
>> +        return 0;
>> +    }
>
> I think you want "vmstart" here?

NO, we want to check the change of VM runstate, not just *start* action.;)

>> +
>>       if (!sender->peer) {
>>           return 1;
>>       }
>
>
> .
>