net/9p: autoload transport modules

Automatically load transport modules based on the trans= parameter
passed to mount.
This removes the requirement for the user to know which module to use.

Link: http://lkml.kernel.org/r/20211017134611.4330-1-linux@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

include/net/9p/transport.h

@@ -11,6 +11,8 @@
 #ifndef NET_9P_TRANSPORT_H
 #define NET_9P_TRANSPORT_H
 
+#include <linux/module.h>
+
 #define P9_DEF_MIN_RESVPORT	(665U)
 #define P9_DEF_MAX_RESVPORT	(1023U)
 
@@ -55,4 +57,8 @@ void v9fs_unregister_trans(struct p9_trans_module *m);
 struct p9_trans_module *v9fs_get_trans_by_name(char *s);
 struct p9_trans_module *v9fs_get_default_trans(void);
 void v9fs_put_trans(struct p9_trans_module *m);
+
+#define MODULE_ALIAS_9P(transport) \
+	MODULE_ALIAS("9p-" transport)
+
 #endif /* NET_9P_TRANSPORT_H */

net/9p/mod.c

@@ -12,6 +12,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
+#include <linux/kmod.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
 #include <linux/moduleparam.h>
@@ -87,12 +88,7 @@ void v9fs_unregister_trans(struct p9_trans_module *m)
 }
 EXPORT_SYMBOL(v9fs_unregister_trans);
 
-/**
- * v9fs_get_trans_by_name - get transport with the matching name
- * @s: string identifying transport
- *
- */
-struct p9_trans_module *v9fs_get_trans_by_name(char *s)
+static struct p9_trans_module *_p9_get_trans_by_name(char *s)
 {
 	struct p9_trans_module *t, *found = NULL;
 
@@ -106,6 +102,28 @@ struct p9_trans_module *v9fs_get_trans_by_name(char *s)
 		}
 
 	spin_unlock(&v9fs_trans_lock);
+
+	return found;
+}
+
+/**
+ * v9fs_get_trans_by_name - get transport with the matching name
+ * @s: string identifying transport
+ *
+ */
+struct p9_trans_module *v9fs_get_trans_by_name(char *s)
+{
+	struct p9_trans_module *found = NULL;
+
+	found = _p9_get_trans_by_name(s);
+
+#ifdef CONFIG_MODULES
+	if (!found) {
+		request_module("9p-%s", s);
+		found = _p9_get_trans_by_name(s);
+	}
+#endif
+
 	return found;
 }
 EXPORT_SYMBOL(v9fs_get_trans_by_name);

net/9p/trans_rdma.c

@@ -767,6 +767,7 @@ static void __exit p9_trans_rdma_exit(void)
 
 module_init(p9_trans_rdma_init);
 module_exit(p9_trans_rdma_exit);
+MODULE_ALIAS_9P("rdma");
 
 MODULE_AUTHOR("Tom Tucker <tom@opengridcomputing.com>");
 MODULE_DESCRIPTION("RDMA Transport for 9P");

net/9p/trans_virtio.c

@@ -794,6 +794,7 @@ static void __exit p9_virtio_cleanup(void)
 
 module_init(p9_virtio_init);
 module_exit(p9_virtio_cleanup);
+MODULE_ALIAS_9P("virtio");
 
 MODULE_DEVICE_TABLE(virtio, id_table);
 MODULE_AUTHOR("Eric Van Hensbergen <ericvh@gmail.com>");

net/9p/trans_xen.c

@@ -552,6 +552,7 @@ static int p9_trans_xen_init(void)
 	return rc;
 }
 module_init(p9_trans_xen_init);
+MODULE_ALIAS_9P("xen");
 
 static void p9_trans_xen_exit(void)
 {