[PATCH v4 13/26] vhost: add API to set max queue pairs

[Maxime Coquelin <maxime.coquelin@redhat.com>]

This patch introduces a new rte_vhost_driver_set_max_queues
API as preliminary work for multiqueue support with VDUSE.

Indeed, with VDUSE we need to pre-allocate the vrings at
device creation time, so we need such API not to allocate
the 128 queue pairs supported by the Vhost library.

Calling the API is optional, 128 queue pairs remaining the
default.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 doc/guides/prog_guide/vhost_lib.rst    |  4 +++
 doc/guides/rel_notes/release_23_07.rst |  5 ++++
 lib/vhost/rte_vhost.h                  | 17 ++++++++++++
 lib/vhost/socket.c                     | 36 ++++++++++++++++++++++++--
 lib/vhost/version.map                  |  1 +
 5 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index 0f964d7a4a..0c2b4d020a 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -339,6 +339,10 @@ The following is an overview of some key Vhost API functions:
   Inject the offloaded interrupt received by the 'guest_notify' callback,
   into the vhost device's queue.
 
+* ``rte_vhost_driver_set_max_queue_num(const char *path, uint32_t max_queue_pairs)``
+
+  Set the maximum number of queue pairs supported by the device.
+
 Vhost-user Implementations
 --------------------------
 
diff --git a/doc/guides/rel_notes/release_23_07.rst b/doc/guides/rel_notes/release_23_07.rst
index 3eed8ac561..7034fb664c 100644
--- a/doc/guides/rel_notes/release_23_07.rst
+++ b/doc/guides/rel_notes/release_23_07.rst
@@ -62,6 +62,11 @@ New Features
   rte_vhost_notify_guest(), is added to raise the interrupt outside of the
   fast path.
 
+* **Added Vhost API to set maximum queue pairs supported.**
+
+  Introduced ``rte_vhost_driver_set_max_queue_num()`` to be able to limit the
+  maximum number of supported queue pairs, required for VDUSE support.
+
 
 Removed Items
 -------------
diff --git a/lib/vhost/rte_vhost.h b/lib/vhost/rte_vhost.h
index 7a10bc36cf..7844c9f142 100644
--- a/lib/vhost/rte_vhost.h
+++ b/lib/vhost/rte_vhost.h
@@ -609,6 +609,23 @@ rte_vhost_driver_get_protocol_features(const char *path,
 int
 rte_vhost_driver_get_queue_num(const char *path, uint32_t *queue_num);
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice.
+ *
+ * Set the maximum number of queue pairs supported by the device.
+ *
+ * @param path
+ *  The vhost-user socket file path
+ * @param max_queue_pairs
+ *  The maximum number of queue pairs
+ * @return
+ *  0 on success, -1 on failure
+ */
+__rte_experimental
+int
+rte_vhost_driver_set_max_queue_num(const char *path, uint32_t max_queue_pairs);
+
 /**
  * Get the feature bits after negotiation
  *
diff --git a/lib/vhost/socket.c b/lib/vhost/socket.c
index 407d0011c3..29f7a8cece 100644
--- a/lib/vhost/socket.c
+++ b/lib/vhost/socket.c
@@ -57,6 +57,8 @@ struct vhost_user_socket {
 
 	uint64_t protocol_features;
 
+	uint32_t max_queue_pairs;
+
 	struct rte_vdpa_device *vdpa_dev;
 
 	struct rte_vhost_device_ops const *notify_ops;
@@ -823,7 +825,7 @@ rte_vhost_driver_get_queue_num(const char *path, uint32_t *queue_num)
 
 	vdpa_dev = vsocket->vdpa_dev;
 	if (!vdpa_dev) {
-		*queue_num = VHOST_MAX_QUEUE_PAIRS;
+		*queue_num = vsocket->max_queue_pairs;
 		goto unlock_exit;
 	}
 
@@ -833,7 +835,36 @@ rte_vhost_driver_get_queue_num(const char *path, uint32_t *queue_num)
 		goto unlock_exit;
 	}
 
-	*queue_num = RTE_MIN((uint32_t)VHOST_MAX_QUEUE_PAIRS, vdpa_queue_num);
+	*queue_num = RTE_MIN(vsocket->max_queue_pairs, vdpa_queue_num);
+
+unlock_exit:
+	pthread_mutex_unlock(&vhost_user.mutex);
+	return ret;
+}
+
+int
+rte_vhost_driver_set_max_queue_num(const char *path, uint32_t max_queue_pairs)
+{
+	struct vhost_user_socket *vsocket;
+	int ret = 0;
+
+	VHOST_LOG_CONFIG(path, INFO, "Setting max queue pairs to %u\n", max_queue_pairs);
+
+	if (max_queue_pairs > VHOST_MAX_QUEUE_PAIRS) {
+		VHOST_LOG_CONFIG(path, ERR, "Library only supports up to %u queue pairs\n",
+				VHOST_MAX_QUEUE_PAIRS);
+		return -1;
+	}
+
+	pthread_mutex_lock(&vhost_user.mutex);
+	vsocket = find_vhost_user_socket(path);
+	if (!vsocket) {
+		VHOST_LOG_CONFIG(path, ERR, "socket file is not registered yet.\n");
+		ret = -1;
+		goto unlock_exit;
+	}
+
+	vsocket->max_queue_pairs = max_queue_pairs;
 
 unlock_exit:
 	pthread_mutex_unlock(&vhost_user.mutex);
@@ -889,6 +920,7 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 		goto out_free;
 	}
 	vsocket->vdpa_dev = NULL;
+	vsocket->max_queue_pairs = VHOST_MAX_QUEUE_PAIRS;
 	vsocket->extbuf = flags & RTE_VHOST_USER_EXTBUF_SUPPORT;
 	vsocket->linearbuf = flags & RTE_VHOST_USER_LINEARBUF_SUPPORT;
 	vsocket->async_copy = flags & RTE_VHOST_USER_ASYNC_COPY;
diff --git a/lib/vhost/version.map b/lib/vhost/version.map
index 7bcbfd12cf..5051c29022 100644
--- a/lib/vhost/version.map
+++ b/lib/vhost/version.map
@@ -107,6 +107,7 @@ EXPERIMENTAL {
 
         # added in 23.07
 	rte_vhost_notify_guest;
+	rte_vhost_driver_set_max_queue_num;
 };
 
 INTERNAL {
-- 
2.40.1