[v3,15/28] vhost: add API to set max queue pairs

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index e8bb8c9b7b..cd4b109139 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -334,6 +334,10 @@  The following is an overview of some key Vhost API functions:
   Clean DMA vChannel finished to use. After this function is called,
   the specified DMA vChannel should no longer be used by the Vhost library.
 
+* ``rte_vhost_driver_set_max_queue_num(path, 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 a9b1293689..fa889a5ee7 100644
--- a/doc/guides/rel_notes/release_23_07.rst
+++ b/doc/guides/rel_notes/release_23_07.rst
@@ -55,6 +55,11 @@  New Features
      Also, make sure to start the actual text at the margin.
      =======================================================
 
+* **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 58a5d4be92..44cbfcb469 100644
--- a/lib/vhost/rte_vhost.h
+++ b/lib/vhost/rte_vhost.h
@@ -588,6 +588,23 @@  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 ba54263824..e95c3ffeac 100644
--- a/lib/vhost/socket.c
+++ b/lib/vhost/socket.c
@@ -56,6 +56,8 @@  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;
@@ -821,7 +823,7 @@  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;
 	}
 
@@ -831,7 +833,36 @@  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);
@@ -890,6 +921,7 @@  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 d322a4a888..dffb126aa8 100644
--- a/lib/vhost/version.map
+++ b/lib/vhost/version.map
@@ -98,6 +98,9 @@  EXPERIMENTAL {
 	# added in 22.11
 	rte_vhost_async_dma_unconfigure;
 	rte_vhost_vring_call_nonblock;
+
+	# added in 23.07
+	rte_vhost_driver_set_max_queue_num;
 };
 
 INTERNAL {