Re: [PATCH] OvmfPkg/VirtioScsiDxe: Allocate all required vrings at VirtioScsiInit

["zhengxiang (A)" <zhengxiang9@huawei.com>]

On 2017/12/14 17:06, Paolo Bonzini wrote:
> On 14/12/2017 07:55, zhengxiang (A) wrote:
>> Hello Laszlo and Paolo,
>>
>> Thanks for your review!
>>
>> On 2017/12/13 19:16, Laszlo Ersek wrote:
>>> On 12/13/17 10:29, Paolo Bonzini wrote:
>>>> On 13/12/2017 09:35, Laszlo Ersek wrote:
>>>>> Perhaps you can update vhost-scsi similarly to the last patch of
>>>>> Maxime's v4 series, even without "VIRTIO_SCSI_F_MQ" -- in the
>>>>> SET_FEATURES request handler, just destroy the unused virtqueues that
>>>>> have not been configured by the guest driver until that time?
>>>> Yes, this is the right solution.  We can assume that if the descriptor
>>>> address is equal to zero, the queue is not in use.  This is not in the
>>>> spec as far as I can see, but it is QEMU's assumption.  I will send a
>>>> patch to the virtio specification.
>>
>> I would try this solution! However, is there any possibility that the allocated
>> descriptor address is exactly equal to zero and the queue is in use?
> 
> That would break QEMU's virtio implementation, so it's pretty unlikely.
> 
> Paolo
> 

So could I judge the not-in-use queues by adding the below sentence in order
to skip calling vhost_virtqueue_start?

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index e4290ce..05c3322 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1532,6 +1532,7 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
         goto fail_mem;
     }
     for (i = 0; i < hdev->nvqs; ++i) {
+        if (virtio_queue_get_desc_addr(vdev, i) == 0) continue;
         r = vhost_virtqueue_start(hdev,
                                   vdev,
                                   hdev->vqs + i,


Thanks,
Xiang