Re: [RFC v3 4/6] qmp: add QMP command x-debug-virtio-queue-status

[Jason Wang <jasowang@redhat.com>]

On 2020/5/15 下午11:16, Laurent Vivier wrote:
> On 08/05/2020 04:57, Jason Wang wrote:
>> On 2020/5/7 下午7:49, Laurent Vivier wrote:
>>> This new command shows internal status of a VirtQueue.
>>> (vrings and indexes).
>>>
>>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
>>
>> It looks to me that packed virtqueue is not supported. It's better to
>> add them in the future.
> I agree, it's why the series still remains an "RFC".
>
> ...
>>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>>> index 59bf6ef651a6..57552bf05014 100644
>>> --- a/hw/virtio/virtio.c
>>> +++ b/hw/virtio/virtio.c
>>> @@ -3877,6 +3877,41 @@ static VirtIODevice *virtio_device_find(const
>>> char *path)
>>>        return NULL;
>>>    }
>>>    +VirtQueueStatus *qmp_x_debug_virtio_queue_status(const char *path,
>>> +                                                 uint16_t queue,
>>> Error **errp)
>>> +{
>>> +    VirtIODevice *vdev;
>>> +    VirtQueueStatus *status;
>>> +
>>> +    vdev = virtio_device_find(path);
>>> +    if (vdev == NULL) {
>>> +        error_setg(errp, "Path %s is not a VirtIO device", path);
>>> +        return NULL;
>>> +    }
>>> +
>>> +    if (queue >= VIRTIO_QUEUE_MAX || !virtio_queue_get_num(vdev,
>>> queue)) {
>>> +        error_setg(errp, "Invalid virtqueue number %d", queue);
>>> +        return NULL;
>>> +    }
>>> +
>>> +    status = g_new0(VirtQueueStatus, 1);
>>> +    status->queue_index = vdev->vq[queue].queue_index;
>>> +    status->inuse = vdev->vq[queue].inuse;
>>> +    status->vring_num = vdev->vq[queue].vring.num;
>>> +    status->vring_num_default = vdev->vq[queue].vring.num_default;
>>> +    status->vring_align = vdev->vq[queue].vring.align;
>>> +    status->vring_desc = vdev->vq[queue].vring.desc;
>>> +    status->vring_avail = vdev->vq[queue].vring.avail;
>>> +    status->vring_used = vdev->vq[queue].vring.used;
>>> +    status->last_avail_idx = vdev->vq[queue].last_avail_idx;
>>
>> This might not be correct when vhost is used.
>>
>> We may consider to sync last_avail_idx from vhost backends here?
> Yes, but I don't know how to do that. Where can I find the information?


It could be synced through vhost ops vhost_get_vring_base(), see 
vhost_virtqueue_stop().

Thanks


>
> Thanks,
> Laurent