[PATCH] virtio_net: Enable MSI-X vector for ctrl queue

When we use vhost-user backend on the host, MSI-X vector should be set
so that the vmm can get an irq FD and send it to the backend device
process with vhost-user protocol.
Since whether the vector is set for a queue is determined depending on
the queue has a callback, this commit sets an empty callback for
virtio-net's control queue.

Signed-off-by: Keiichi Watanabe <redacted>
---
 drivers/net/virtio_net.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 11f722460513..002e3695d4b3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2696,6 +2696,11 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
 	virtnet_free_queues(vi);
 }
 
+static void virtnet_ctrlq_done(struct virtqueue *rvq)
+{
+	/* Do nothing */
+}
+
 /* How large should a single buffer be so a queue full of these can fit at
  * least one full packet?
  * Logic below assumes the mergeable buffer header is used.

@@ -2748,7 +2753,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
 
 	/* Parameters for control virtqueue, if any */
 	if (vi->has_cvq) {
-		callbacks[total_vqs - 1] = NULL;
+		callbacks[total_vqs - 1] = virtnet_ctrlq_done;
 		names[total_vqs - 1] = "control";
 	}
 

-- 
2.32.0.288.g62a8d224e6-goog

On Fri, Jun 18, 2021 at 04:26:25PM +0900, Keiichi Watanabe wrote:

When we use vhost-user backend on the host, MSI-X vector should be set
so that the vmm can get an irq FD and send it to the backend device
process with vhost-user protocol.
Since whether the vector is set for a queue is determined depending on
the queue has a callback, this commit sets an empty callback for
virtio-net's control queue.

Signed-off-by: Keiichi Watanabe <redacted>

I'm confused by this explanation. If the vmm wants to get
an interrupt it can do so - why change the guest driver?

在 2021/6/18 下午8:38, Michael S. Tsirkin 写道:

On Fri, Jun 18, 2021 at 04:26:25PM +0900, Keiichi Watanabe wrote:

quoted

When we use vhost-user backend on the host, MSI-X vector should be set
so that the vmm can get an irq FD and send it to the backend device
process with vhost-user protocol.
Since whether the vector is set for a queue is determined depending on
the queue has a callback, this commit sets an empty callback for
virtio-net's control queue.

Signed-off-by: Keiichi Watanabe <redacted>

I'm confused by this explanation. If the vmm wants to get
an interrupt it can do so - why change the guest driver?

+1, it sounds like a bug in the backend or we probably need more context 
here.

Thanks

quoted

---
  drivers/net/virtio_net.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 11f722460513..002e3695d4b3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2696,6 +2696,11 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
  	virtnet_free_queues(vi);
  }
  
+static void virtnet_ctrlq_done(struct virtqueue *rvq)
+{
+	/* Do nothing */
+}
+
  /* How large should a single buffer be so a queue full of these can fit at
   * least one full packet?
   * Logic below assumes the mergeable buffer header is used.

@@ -2748,7 +2753,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
  
  	/* Parameters for control virtqueue, if any */
  	if (vi->has_cvq) {
-		callbacks[total_vqs - 1] = NULL;
+		callbacks[total_vqs - 1] = virtnet_ctrlq_done;
  		names[total_vqs - 1] = "control";
  	}
  

-- 
2.32.0.288.g62a8d224e6-goog