dm log: auto load modules

If the log type is not recognised, attempt to load the module
'dm-log-<type>.ko'.
Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-log.c

@@ -41,7 +41,7 @@ int dm_unregister_dirty_log_type(struct dirty_log_type *type)
 	return 0;
 }
 
-static struct dirty_log_type *get_type(const char *type_name)
+static struct dirty_log_type *_get_type(const char *type_name)
 {
 	struct dirty_log_type *type;
 
@@ -61,6 +61,55 @@ static struct dirty_log_type *get_type(const char *type_name)
 	return NULL;
 }
 
+/*
+ * get_type
+ * @type_name
+ *
+ * Attempt to retrieve the dirty_log_type by name.  If not already
+ * available, attempt to load the appropriate module.
+ *
+ * Log modules are named "dm-log-" followed by the 'type_name'.
+ * Modules may contain multiple types.
+ * This function will first try the module "dm-log-<type_name>",
+ * then truncate 'type_name' on the last '-' and try again.
+ *
+ * For example, if type_name was "clustered-disk", it would search
+ * 'dm-log-clustered-disk' then 'dm-log-clustered'.
+ *
+ * Returns: dirty_log_type* on success, NULL on failure
+ */
+static struct dirty_log_type *get_type(const char *type_name)
+{
+	char *p, *type_name_dup;
+	struct dirty_log_type *type;
+
+	type = _get_type(type_name);
+	if (type)
+		return type;
+
+	type_name_dup = kstrdup(type_name, GFP_KERNEL);
+	if (!type_name_dup) {
+		DMWARN("No memory left to attempt log module load for \"%s\"",
+		       type_name);
+		return NULL;
+	}
+
+	while (request_module("dm-log-%s", type_name_dup) ||
+	       !(type = _get_type(type_name))) {
+		p = strrchr(type_name_dup, '-');
+		if (!p)
+			break;
+		p[0] = '\0';
+	}
+
+	if (!type)
+		DMWARN("Module for logging type \"%s\" not found.", type_name);
+
+	kfree(type_name_dup);
+
+	return type;
+}
+
 static void put_type(struct dirty_log_type *type)
 {
 	spin_lock(&_lock);