vhost: add flag for built-in virtio driver

The librte_vhost API is used in two ways:
1. As a vhost net device backend via rte_vhost_enqueue/dequeue_burst().
2. As a library for implementing vhost device backends.

There is no distinction between the two at the API level or in the
librte_vhost implementation.  For example, device state is kept in
"struct virtio_net" regardless of whether this is actually a net device
backend or whether the built-in virtio_net.c driver is in use.

The virtio_net.c driver should be a librte_vhost API client just like
the vhost-scsi code and have no special access to vhost.h internals.
Unfortunately, fixing this requires significant librte_vhost API
changes.

This patch takes a different approach: keep the librte_vhost API
unchanged but track whether the built-in virtio_net.c driver is in use.
See the next patch for a bug fix that requires knowledge of whether
virtio_net.c is in use.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>

lib/librte_vhost/socket.c

@@ -40,6 +40,7 @@ struct vhost_user_socket {
 	bool reconnect;
 	bool dequeue_zero_copy;
 	bool iommu_support;
+	bool use_builtin_virtio_net;
 
 	/*
 	 * The "supported_features" indicates the feature bits the
@@ -195,6 +196,8 @@ vhost_user_add_connection(int fd, struct vhost_user_socket *vsocket)
 	size = strnlen(vsocket->path, PATH_MAX);
 	vhost_set_ifname(vid, vsocket->path, size);
 
+	vhost_set_builtin_virtio_net(vid, vsocket->use_builtin_virtio_net);
+
 	if (vsocket->dequeue_zero_copy)
 		vhost_enable_dequeue_zero_copy(vid);
 
@@ -527,6 +530,12 @@ rte_vhost_driver_disable_features(const char *path, uint64_t features)
 
 	pthread_mutex_lock(&vhost_user.mutex);
 	vsocket = find_vhost_user_socket(path);
+
+	/* Note that use_builtin_virtio_net is not affected by this function
+	 * since callers may want to selectively disable features of the
+	 * built-in vhost net device backend.
+	 */
+
 	if (vsocket)
 		vsocket->features &= ~features;
 	pthread_mutex_unlock(&vhost_user.mutex);
@@ -567,6 +576,11 @@ rte_vhost_driver_set_features(const char *path, uint64_t features)
 	if (vsocket) {
 		vsocket->supported_features = features;
 		vsocket->features = features;
+
+		/* Anyone setting feature bits is implementing their own vhost
+		 * device backend.
+		 */
+		vsocket->use_builtin_virtio_net = false;
 	}
 	pthread_mutex_unlock(&vhost_user.mutex);
 
@@ -647,6 +661,7 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 	 * rte_vhost_driver_set_features(), which will overwrite following
 	 * two values.
 	 */
+	vsocket->use_builtin_virtio_net = true;
 	vsocket->supported_features = VIRTIO_NET_SUPPORTED_FEATURES;
 	vsocket->features           = VIRTIO_NET_SUPPORTED_FEATURES;
 

lib/librte_vhost/vhost.c

@@ -251,7 +251,7 @@ reset_device(struct virtio_net *dev)
 
 	dev->features = 0;
 	dev->protocol_features = 0;
-	dev->flags = 0;
+	dev->flags &= VIRTIO_DEV_BUILTIN_VIRTIO_NET;
 
 	for (i = 0; i < dev->nr_vring; i++)
 		reset_vring_queue(dev, i);
@@ -287,6 +287,7 @@ vhost_new_device(void)
 
 	vhost_devices[i] = dev;
 	dev->vid = i;
+	dev->flags = VIRTIO_DEV_BUILTIN_VIRTIO_NET;
 	dev->slave_req_fd = -1;
 
 	return i;
@@ -343,6 +344,20 @@ vhost_enable_dequeue_zero_copy(int vid)
 	dev->dequeue_zero_copy = 1;
 }
 
+void
+vhost_set_builtin_virtio_net(int vid, bool enable)
+{
+	struct virtio_net *dev = get_device(vid);
+
+	if (dev == NULL)
+		return;
+
+	if (enable)
+		dev->flags |= VIRTIO_DEV_BUILTIN_VIRTIO_NET;
+	else
+		dev->flags &= ~VIRTIO_DEV_BUILTIN_VIRTIO_NET;
+}
+
 int
 rte_vhost_get_mtu(int vid, uint16_t *mtu)
 {

lib/librte_vhost/vhost.h

@@ -24,6 +24,8 @@
 #define VIRTIO_DEV_RUNNING 1
 /* Used to indicate that the device is ready to operate */
 #define VIRTIO_DEV_READY 2
+/* Used to indicate that the built-in vhost net device backend is enabled */
+#define VIRTIO_DEV_BUILTIN_VIRTIO_NET 4
 
 /* Backend value set by guest. */
 #define VIRTIO_DEV_STOPPED -1
@@ -357,6 +359,7 @@ int alloc_vring_queue(struct virtio_net *dev, uint32_t vring_idx);
 
 void vhost_set_ifname(int, const char *if_name, unsigned int if_len);
 void vhost_enable_dequeue_zero_copy(int vid);
+void vhost_set_builtin_virtio_net(int vid, bool enable);
 
 struct vhost_device_ops const *vhost_driver_callback_get(const char *path);
 

lib/librte_vhost/virtio_net.c

@@ -703,6 +703,13 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 	if (!dev)
 		return 0;
 
+	if (unlikely(!(dev->flags & VIRTIO_DEV_BUILTIN_VIRTIO_NET))) {
+		RTE_LOG(ERR, VHOST_DATA,
+			"(%d) %s: built-in vhost net backend is disabled.\n",
+			dev->vid, __func__);
+		return 0;
+	}
+
 	if (dev->features & (1 << VIRTIO_NET_F_MRG_RXBUF))
 		return virtio_dev_merge_rx(dev, queue_id, pkts, count);
 	else
@@ -1128,6 +1135,13 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 	if (!dev)
 		return 0;
 
+	if (unlikely(!(dev->flags & VIRTIO_DEV_BUILTIN_VIRTIO_NET))) {
+		RTE_LOG(ERR, VHOST_DATA,
+			"(%d) %s: built-in vhost net backend is disabled.\n",
+			dev->vid, __func__);
+		return 0;
+	}
+
 	if (unlikely(!is_valid_virt_queue_idx(queue_id, 1, dev->nr_vring))) {
 		RTE_LOG(ERR, VHOST_DATA, "(%d) %s: invalid virtqueue idx %d.\n",
 			dev->vid, __func__, queue_id);