+/*
+ * Send command via the control virtqueue and check status. Commands
+ * supported by the hypervisor, as indicated by feature bits, should
+ * never fail unless improperly formated.
+ */
+static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
+ struct scatterlist *data, int out, int in)
+{
+ struct scatterlist *s, sg[VIRTNET_SEND_COMMAND_SG_MAX + 2];
+ struct virtio_net_ctrl_hdr ctrl;
+ virtio_net_ctrl_ack status = ~0;
+ unsigned int tmp;
+ int i;
+
+ /* Caller should know better */
+ BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ) ||
+ (out + in > VIRTNET_SEND_COMMAND_SG_MAX));
+
+ out++; /* Add header */
+ in++; /* Add return status */
+
+ ctrl.class = class;
+ ctrl.cmd = cmd;
+
+ sg_init_table(sg, out + in);
+
+ sg_set_buf(&sg[0], &ctrl, sizeof(ctrl));
+ for_each_sg(data, s, out + in - 2, i)
+ sg_set_buf(&sg[i + 1], sg_virt(s), s->length);
+ sg_set_buf(&sg[out + in - 1], &status, sizeof(status));
+
+ BUG_ON(virtqueue_add_buf(vi->cvq, sg, out, in, vi, GFP_ATOMIC) < 0);
+
+ virtqueue_kick(vi->cvq);
+
+ /* Spin for a response, the kick causes an ioport write, trapping
+ * into the hypervisor, so the request should be handled immediately.
+ */
+ while (!virtqueue_get_buf(vi->cvq, &tmp))
+ cpu_relax();
+
+ return status == VIRTIO_NET_OK;
+}
+