RDMA: Add NLDEV_GET_CHARDEV to allow char dev discovery and autoload

Allow userspace to issue a netlink query against the ib_device for
something like "uverbs" and get back the char dev name, inode major/minor,
and interface ABI information for "uverbs0".

Since we are now in netlink this can also trigger a module autoload to
make the uverbs device come into existence.

Largely this will let us replace searching and reading inside sysfs to
setup devices, and provides an alternative (using driver_id) to device
name based provider binding for things like rxe.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

include/rdma/ib_verbs.h

@@ -2684,10 +2684,14 @@ struct ib_device {
 	u32 iw_driver_flags;
 };
 
+struct ib_client_nl_info;
 struct ib_client {
 	const char *name;
 	void (*add)   (struct ib_device *);
 	void (*remove)(struct ib_device *, void *client_data);
+	int (*get_nl_info)(struct ib_device *ibdev, void *client_data,
+			   struct ib_client_nl_info *res);
+	int (*get_global_nl_info)(struct ib_client_nl_info *res);
 
 	/* Returns the net_dev belonging to this ib_client and matching the
 	 * given parameters.

include/rdma/rdma_netlink.h

@@ -110,4 +110,6 @@ void rdma_link_register(struct rdma_link_ops *ops);
 void rdma_link_unregister(struct rdma_link_ops *ops);
 
 #define MODULE_ALIAS_RDMA_LINK(type) MODULE_ALIAS("rdma-link-" type)
+#define MODULE_ALIAS_RDMA_CLIENT(type) MODULE_ALIAS("rdma-client-" type)
+
 #endif /* _RDMA_NETLINK_H */