vhost: introduce API to start a specific driver

We used to use rte_vhost_driver_session_start() to trigger the vhost-user
session. It takes no argument, thus it's a global trigger. And it could
be problematic.

The issue is, currently, rte_vhost_driver_register(path, flags) actually
tries to put it into the session loop (by fdset_add). However, it needs
a set of APIs to set a vhost-user driver properly:
  * rte_vhost_driver_register(path, flags);
  * rte_vhost_driver_set_features(path, features);
  * rte_vhost_driver_callback_register(path, vhost_device_ops);

If a new vhost-user driver is registered after the trigger (think OVS-DPDK
that could add a port dynamically from cmdline), the current code will
effectively starts the session for the new driver just after the first
API rte_vhost_driver_register() is invoked, leaving later calls taking
no effect at all.

To handle the case properly, this patch introduce a new API,
rte_vhost_driver_start(path), to trigger a specific vhost-user driver.
To do that, the rte_vhost_driver_register(path, flags) is simplified
to create the socket only and let rte_vhost_driver_start(path) to
actually put it into the session loop.

Meanwhile, the rte_vhost_driver_session_start is removed: we could hide
the session thread internally (create the thread if it has not been
created). This would also simplify the application.

NOTE: the API order in prog guide is slightly adjusted for showing the
correct invoke order.

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

doc/guides/prog_guide/vhost_lib.rst

@@ -116,12 +116,6 @@ The following is an overview of some key Vhost API functions:
   vhost-user driver could be vhost-user net, yet it could be something else,
   say, vhost-user SCSI.
 
-* ``rte_vhost_driver_session_start()``
-
-  This function starts the vhost session loop to handle vhost messages. It
-  starts an infinite loop, therefore it should be called in a dedicated
-  thread.
-
 * ``rte_vhost_driver_callback_register(path, vhost_device_ops)``
 
   This function registers a set of callbacks, to let DPDK applications take
@@ -149,6 +143,17 @@ The following is an overview of some key Vhost API functions:
     ``VHOST_F_LOG_ALL`` will be set/cleared at the start/end of live
     migration, respectively.
 
+* ``rte_vhost_driver_disable/enable_features(path, features))``
+
+  This function disables/enables some features. For example, it can be used to
+  disable mergeable buffers and TSO features, which both are enabled by
+  default.
+
+* ``rte_vhost_driver_start(path)``
+
+  This function triggers the vhost-user negotiation. It should be invoked at
+  the end of initializing a vhost-user driver.
+
 * ``rte_vhost_enqueue_burst(vid, queue_id, pkts, count)``
 
   Transmits (enqueues) ``count`` packets from host to guest.
@@ -157,13 +162,6 @@ The following is an overview of some key Vhost API functions:
 
   Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``.
 
-* ``rte_vhost_driver_disable/enable_features(path, features))``
-
-  This function disables/enables some features. For example, it can be used to
-  disable mergeable buffers and TSO features, which both are enabled by
-  default.
-
-
 Vhost-user Implementations
 --------------------------
 

doc/guides/rel_notes/release_17_05.rst

@@ -315,6 +315,10 @@ API Changes
   * The vhost struct ``virtio_net_device_ops`` is renamed to
     ``vhost_device_ops``
 
+  * The vhost API ``rte_vhost_driver_session_start`` is removed. Instead,
+    ``rte_vhost_driver_start`` should be used, and no need to create a
+    thread to call it.
+
 
 ABI Changes
 -----------

drivers/net/vhost/rte_eth_vhost.c

@@ -128,9 +128,6 @@ static struct internal_list_head internal_list =
 
 static pthread_mutex_t internal_list_lock = PTHREAD_MUTEX_INITIALIZER;
 
-static rte_atomic16_t nb_started_ports;
-static pthread_t session_th;
-
 static struct rte_eth_link pmd_link = {
 		.link_speed = 10000,
 		.link_duplex = ETH_LINK_FULL_DUPLEX,
@@ -769,42 +766,6 @@ rte_eth_vhost_get_vid_from_port_id(uint8_t port_id)
 	return vid;
 }
 
-static void *
-vhost_driver_session(void *param __rte_unused)
-{
-	/* start event handling */
-	rte_vhost_driver_session_start();
-
-	return NULL;
-}
-
-static int
-vhost_driver_session_start(void)
-{
-	int ret;
-
-	ret = pthread_create(&session_th,
-			NULL, vhost_driver_session, NULL);
-	if (ret)
-		RTE_LOG(ERR, PMD, "Can't create a thread\n");
-
-	return ret;
-}
-
-static void
-vhost_driver_session_stop(void)
-{
-	int ret;
-
-	ret = pthread_cancel(session_th);
-	if (ret)
-		RTE_LOG(ERR, PMD, "Can't cancel the thread\n");
-
-	ret = pthread_join(session_th, NULL);
-	if (ret)
-		RTE_LOG(ERR, PMD, "Can't join the thread\n");
-}
-
 static int
 eth_dev_start(struct rte_eth_dev *dev)
 {
@@ -1120,10 +1081,10 @@ eth_dev_vhost_create(const char *name, char *iface_name, int16_t queues,
 		goto error;
 	}
 
-	/* We need only one message handling thread */
-	if (rte_atomic16_add_return(&nb_started_ports, 1) == 1) {
-		if (vhost_driver_session_start())
-			goto error;
+	if (rte_vhost_driver_start(iface_name) < 0) {
+		RTE_LOG(ERR, PMD, "Failed to start driver for %s\n",
+			iface_name);
+		goto error;
 	}
 
 	return data->port_id;
@@ -1250,9 +1211,6 @@ rte_pmd_vhost_remove(const char *name)
 
 	eth_dev_close(eth_dev);
 
-	if (rte_atomic16_sub_return(&nb_started_ports, 1) == 0)
-		vhost_driver_session_stop();
-
 	rte_free(vring_states[eth_dev->data->port_id]);
 	vring_states[eth_dev->data->port_id] = NULL;
 

examples/tep_termination/main.c

@@ -1263,7 +1263,13 @@ main(int argc, char *argv[])
 			"failed to register vhost driver callbacks.\n");
 	}
 
-	rte_vhost_driver_session_start();
+	if (rte_vhost_driver_start(dev_basename) < 0) {
+		rte_exit(EXIT_FAILURE,
+			"failed to start vhost driver.\n");
+	}
+
+	RTE_LCORE_FOREACH_SLAVE(lcore_id)
+		rte_eal_wait_lcore(lcore_id);
 
 	return 0;
 }

examples/vhost/main.c

@@ -1545,9 +1545,16 @@ main(int argc, char *argv[])
 			rte_exit(EXIT_FAILURE,
 				"failed to register vhost driver callbacks.\n");
 		}
+
+		if (rte_vhost_driver_start(file) < 0) {
+			rte_exit(EXIT_FAILURE,
+				"failed to start vhost driver.\n");
+		}
 	}
 
-	rte_vhost_driver_session_start();
+	RTE_LCORE_FOREACH_SLAVE(lcore_id)
+		rte_eal_wait_lcore(lcore_id);
+
 	return 0;
 
 }

lib/librte_vhost/fd_man.c

@@ -210,8 +210,8 @@ fdset_del(struct fdset *pfdset, int fd)
  * will wait until the flag is reset to zero(which indicates the callback is
  * finished), then it could free the context after fdset_del.
  */
-void
-fdset_event_dispatch(struct fdset *pfdset)
+void *
+fdset_event_dispatch(void *arg)
 {
 	int i;
 	struct pollfd *pfd;
@@ -221,9 +221,10 @@ fdset_event_dispatch(struct fdset *pfdset)
 	int fd, numfds;
 	int remove1, remove2;
 	int need_shrink;
+	struct fdset *pfdset = arg;
 
 	if (pfdset == NULL)
-		return;
+		return NULL;
 
 	while (1) {
 
@@ -294,4 +295,6 @@ fdset_event_dispatch(struct fdset *pfdset)
 		if (need_shrink)
 			fdset_shrink(pfdset);
 	}
+
+	return NULL;
 }

lib/librte_vhost/fd_man.h

@@ -64,6 +64,6 @@ int fdset_add(struct fdset *pfdset, int fd,
 
 void *fdset_del(struct fdset *pfdset, int fd);
 
-void fdset_event_dispatch(struct fdset *pfdset);
+void *fdset_event_dispatch(void *arg);
 
 #endif

lib/librte_vhost/rte_vhost_version.map

@@ -4,7 +4,6 @@ DPDK_2.0 {
 	rte_vhost_dequeue_burst;
 	rte_vhost_driver_callback_register;
 	rte_vhost_driver_register;
-	rte_vhost_driver_session_start;
 	rte_vhost_enable_guest_notification;
 	rte_vhost_enqueue_burst;
 
@@ -35,6 +34,7 @@ DPDK_17.05 {
 	rte_vhost_driver_enable_features;
 	rte_vhost_driver_get_features;
 	rte_vhost_driver_set_features;
+	rte_vhost_driver_start;
 	rte_vhost_get_mem_table;
 	rte_vhost_get_mtu;
 	rte_vhost_get_negotiated_features;

lib/librte_vhost/rte_virtio_net.h

@@ -256,8 +256,19 @@ int rte_vhost_get_negotiated_features(int vid, uint64_t *features);
 /* Register callbacks. */
 int rte_vhost_driver_callback_register(const char *path,
 	struct vhost_device_ops const * const ops);
-/* Start vhost driver session blocking loop. */
-int rte_vhost_driver_session_start(void);
+
+/**
+ *
+ * Start the vhost-user driver.
+ *
+ * This function triggers the vhost-user negotiation.
+ *
+ * @param path
+ *  The vhost-user socket file path
+ * @return
+ *  0 on success, -1 on failure
+ */
+int rte_vhost_driver_start(const char *path);
 
 /**
  * Get the MTU value of the device if set in QEMU.