vdpa: support exposing the count of vqs to userspace

- GET_VQS_COUNT: the count of virtqueues that exposed

Signed-off-by: Longpeng <longpeng2@huawei.com>
Link: https://lore.kernel.org/r/20220315032553.455-4-longpeng2@huawei.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Longpeng &lt;<a href="mailto:longpeng2@huawei.com" target="_blank">longpeng2@huawei.com</a>&gt;<br>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

drivers/vhost/vdpa.c

@@ -373,6 +373,16 @@ static long vhost_vdpa_get_config_size(struct vhost_vdpa *v, u32 __user *argp)
 	return 0;
 }
 
+static long vhost_vdpa_get_vqs_count(struct vhost_vdpa *v, u32 __user *argp)
+{
+	struct vdpa_device *vdpa = v->vdpa;
+
+	if (copy_to_user(argp, &vdpa->nvqs, sizeof(vdpa->nvqs)))
+		return -EFAULT;
+
+	return 0;
+}
+
 static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 				   void __user *argp)
 {
@@ -513,6 +523,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 	case VHOST_VDPA_GET_CONFIG_SIZE:
 		r = vhost_vdpa_get_config_size(v, argp);
 		break;
+	case VHOST_VDPA_GET_VQS_COUNT:
+		r = vhost_vdpa_get_vqs_count(v, argp);
+		break;
 	default:
 		r = vhost_dev_ioctl(&v->vdev, cmd, argp);
 		if (r == -ENOIOCTLCMD)

include/uapi/linux/vhost.h

@@ -154,4 +154,7 @@
 /* Get the config size */
 #define VHOST_VDPA_GET_CONFIG_SIZE	_IOR(VHOST_VIRTIO, 0x79, __u32)
 
+/* Get the count of all virtqueues */
+#define VHOST_VDPA_GET_VQS_COUNT	_IOR(VHOST_VIRTIO, 0x80, __u32)
+
 #endif