RDMA/ucma: Add option to manually set IB path

Export rdma_set_ib_paths to user space to allow applications to
manually set the IB path used for connections.  This allows
alternative ways for a user space application or library to obtain
path record information, including retrieving path information
from cached data, avoiding direct interaction with the IB SA.
The IB SA is a single, centralized entity that can limit scaling
on large clusters running MPI applications.

Future changes to the rdma cm can expand on this framework to
support the full range of features allowed by the IB CM, such as
separate forward and reverse paths and APM.
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Reviewed-By: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/sa_query.c

@@ -604,6 +604,12 @@ retry:
 	return ret ? ret : id;
 }
 
+void ib_sa_unpack_path(void *attribute, struct ib_sa_path_rec *rec)
+{
+	ib_unpack(path_rec_table, ARRAY_SIZE(path_rec_table), attribute, rec);
+}
+EXPORT_SYMBOL(ib_sa_unpack_path);
+
 static void ib_sa_path_rec_callback(struct ib_sa_query *sa_query,
 				    int status,
 				    struct ib_sa_mad *mad)

drivers/infiniband/core/ucma.c

@@ -43,6 +43,7 @@
 #include <rdma/rdma_user_cm.h>
 #include <rdma/ib_marshall.h>
 #include <rdma/rdma_cm.h>
+#include <rdma/rdma_cm_ib.h>
 
 MODULE_AUTHOR("Sean Hefty");
 MODULE_DESCRIPTION("RDMA Userspace Connection Manager Access");
@@ -812,6 +813,51 @@ static int ucma_set_option_id(struct ucma_context *ctx, int optname,
 	return ret;
 }
 
+static int ucma_set_ib_path(struct ucma_context *ctx,
+			    struct ib_path_rec_data *path_data, size_t optlen)
+{
+	struct ib_sa_path_rec sa_path;
+	struct rdma_cm_event event;
+	int ret;
+
+	if (optlen % sizeof(*path_data))
+		return -EINVAL;
+
+	for (; optlen; optlen -= sizeof(*path_data), path_data++) {
+		if (path_data->flags == (IB_PATH_GMP | IB_PATH_PRIMARY |
+					 IB_PATH_BIDIRECTIONAL))
+			break;
+	}
+
+	if (!optlen)
+		return -EINVAL;
+
+	ib_sa_unpack_path(path_data->path_rec, &sa_path);
+	ret = rdma_set_ib_paths(ctx->cm_id, &sa_path, 1);
+	if (ret)
+		return ret;
+
+	memset(&event, 0, sizeof event);
+	event.event = RDMA_CM_EVENT_ROUTE_RESOLVED;
+	return ucma_event_handler(ctx->cm_id, &event);
+}
+
+static int ucma_set_option_ib(struct ucma_context *ctx, int optname,
+			      void *optval, size_t optlen)
+{
+	int ret;
+
+	switch (optname) {
+	case RDMA_OPTION_IB_PATH:
+		ret = ucma_set_ib_path(ctx, optval, optlen);
+		break;
+	default:
+		ret = -ENOSYS;
+	}
+
+	return ret;
+}
+
 static int ucma_set_option_level(struct ucma_context *ctx, int level,
 				 int optname, void *optval, size_t optlen)
 {
@@ -821,6 +867,9 @@ static int ucma_set_option_level(struct ucma_context *ctx, int level,
 	case RDMA_OPTION_ID:
 		ret = ucma_set_option_id(ctx, optname, optval, optlen);
 		break;
+	case RDMA_OPTION_IB:
+		ret = ucma_set_option_ib(ctx, optname, optval, optlen);
+		break;
 	default:
 		ret = -ENOSYS;
 	}

include/rdma/ib_sa.h

@@ -379,4 +379,10 @@ int ib_init_ah_from_path(struct ib_device *device, u8 port_num,
 			 struct ib_sa_path_rec *rec,
 			 struct ib_ah_attr *ah_attr);
 
+/**
+ * ib_sa_unpack_path - Convert a path record from MAD format to struct
+ * ib_sa_path_rec.
+ */
+void ib_sa_unpack_path(void *attribute, struct ib_sa_path_rec *rec);
+
 #endif /* IB_SA_H */

include/rdma/ib_user_sa.h

@@ -35,6 +35,22 @@
 
 #include <linux/types.h>
 
+enum {
+	IB_PATH_GMP		= 1,
+	IB_PATH_PRIMARY		= (1<<1),
+	IB_PATH_ALTERNATE	= (1<<2),
+	IB_PATH_OUTBOUND	= (1<<3),
+	IB_PATH_INBOUND		= (1<<4),
+	IB_PATH_INBOUND_REVERSE = (1<<5),
+	IB_PATH_BIDIRECTIONAL	= IB_PATH_OUTBOUND | IB_PATH_INBOUND_REVERSE
+};
+
+struct ib_path_rec_data {
+	__u32	flags;
+	__u32	reserved;
+	__u32	path_rec[16];
+};
+
 struct ib_user_path_rec {
 	__u8	dgid[16];
 	__u8	sgid[16];

include/rdma/rdma_user_cm.h

@@ -215,12 +215,14 @@ struct rdma_ucm_event_resp {
 
 /* Option levels */
 enum {
-	RDMA_OPTION_ID		= 0
+	RDMA_OPTION_ID		= 0,
+	RDMA_OPTION_IB		= 1
 };
 
 /* Option details */
 enum {
-	RDMA_OPTION_ID_TOS	= 0
+	RDMA_OPTION_ID_TOS	= 0,
+	RDMA_OPTION_IB_PATH	= 1
 };
 
 struct rdma_ucm_set_option {