Index: head/sys/geom/geom.h
===================================================================
--- head/sys/geom/geom.h
+++ head/sys/geom/geom.h
@@ -428,6 +428,7 @@
 void *gctl_get_param(struct gctl_req *req, const char *param, int *len);
 char const *gctl_get_asciiparam(struct gctl_req *req, const char *param);
 void *gctl_get_paraml(struct gctl_req *req, const char *param, int len);
+void *gctl_get_paraml_opt(struct gctl_req *req, const char *param, int len);
 int gctl_error(struct gctl_req *req, const char *fmt, ...) __printflike(2, 3);
 struct g_class *gctl_get_class(struct gctl_req *req, char const *arg);
 struct g_geom *gctl_get_geom(struct gctl_req *req, struct g_class *mpr, char const *arg);
Index: head/sys/geom/geom_ctl.c
===================================================================
--- head/sys/geom/geom_ctl.c
+++ head/sys/geom/geom_ctl.c
@@ -365,18 +365,27 @@
 }
 
 void *
-gctl_get_paraml(struct gctl_req *req, const char *param, int len)
+gctl_get_paraml_opt(struct gctl_req *req, const char *param, int len)
 {
 	int i;
 	void *p;
 
 	p = gctl_get_param(req, param, &i);
-	if (p == NULL)
-		gctl_error(req, "Missing %s argument", param);
-	else if (i != len) {
+	if (i != len) {
 		p = NULL;
 		gctl_error(req, "Wrong length %s argument", param);
 	}
+	return (p);
+}
+
+void *
+gctl_get_paraml(struct gctl_req *req, const char *param, int len)
+{
+	void *p;
+
+	p = gctl_get_paraml_opt(req, param, len);
+	if (p == NULL)
+		gctl_error(req, "Missing %s argument", param);
 	return (p);
 }