vhost: export the number of vrings

We used to use rte_vhost_get_queue_num() for telling how many vrings.
However, the return value is the number of "queue pairs", which is
very virtio-net specific. To make it generic, we should return the
number of vrings instead, and let the driver do the proper translation.
Say, virtio-net driver could turn it to the number of queue pairs by
dividing 2.

Meanwhile, mark rte_vhost_get_queue_num as deprecated.

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

doc/guides/rel_notes/release_17_05.rst

@@ -296,6 +296,9 @@ API Changes
     be per vhost-user socket file. Thus, it takes one more argument:
     ``rte_vhost_driver_callback_register(path, ops)``.
 
+  * The vhost API ``rte_vhost_get_queue_num`` is deprecated, instead,
+    ``rte_vhost_get_vring_num`` should be used.
+
 
 ABI Changes
 -----------

drivers/net/vhost/rte_eth_vhost.c

@@ -595,7 +595,7 @@ new_device(int vid)
 		vq->port = eth_dev->data->port_id;
 	}
 
-	for (i = 0; i < rte_vhost_get_queue_num(vid) * VIRTIO_QNUM; i++)
+	for (i = 0; i < rte_vhost_get_vring_num(vid); i++)
 		rte_vhost_enable_guest_notification(vid, i, 0);
 
 	rte_vhost_get_mtu(vid, &eth_dev->data->mtu);

lib/librte_vhost/rte_vhost_version.map

@@ -39,6 +39,7 @@ DPDK_17.05 {
 	rte_vhost_get_mtu;
 	rte_vhost_get_negotiated_features;
 	rte_vhost_get_vhost_vring;
+	rte_vhost_get_vring_num;
 	rte_vhost_gpa_to_vva;
 
 } DPDK_16.07;

lib/librte_vhost/rte_virtio_net.h

@@ -243,16 +243,33 @@ int rte_vhost_get_mtu(int vid, uint16_t *mtu);
 int rte_vhost_get_numa_node(int vid);
 
 /**
+ * @deprecated
  * Get the number of queues the device supports.
  *
+ * Note this function is deprecated, as it returns a queue pair number,
+ * which is virtio-net specific. Instead, rte_vhost_get_vring_num should
+ * be used.
+ *
  * @param vid
  *  virtio-net device ID
  *
  * @return
  *  The number of queues, 0 on failure
  */
+__rte_deprecated
 uint32_t rte_vhost_get_queue_num(int vid);
 
+/**
+ * Get the number of vrings the device supports.
+ *
+ * @param vid
+ *  vhost device ID
+ *
+ * @return
+ *  The number of vrings, 0 on failure
+ */
+uint16_t rte_vhost_get_vring_num(int vid);
+
 /**
  * Get the virtio net device's ifname, which is the vhost-user socket
  * file path.

lib/librte_vhost/vhost.c

@@ -317,6 +317,17 @@ rte_vhost_get_queue_num(int vid)
 	return dev->nr_vring / 2;
 }
 
+uint16_t
+rte_vhost_get_vring_num(int vid)
+{
+	struct virtio_net *dev = get_device(vid);
+
+	if (dev == NULL)
+		return 0;
+
+	return dev->nr_vring;
+}
+
 int
 rte_vhost_get_ifname(int vid, char *buf, size_t len)
 {