If we get an EPROTONOSUPP error when trying to create the netgraph socket

node, it's most likely because the "ng_socket.ko" KLD is not loaded yet.
So make an attempt to load it before giving up.

usr.sbin/ngctl/main.c

@@ -42,6 +42,7 @@
 #define PROMPT		"+ "
 #define MAX_ARGS	512
 #define WHITESPACE	" \t\r\n\v\f"
+#define NG_SOCKET_KLD	"ng_socket.ko"
 
 /* Internal functions */
 static int	ReadFile(FILE *fp);
@@ -134,8 +135,16 @@ main(int ac, char *av[])
 	av += optind;
 
 	/* Create a new socket node */
-	if (NgMkSockNode(name, &csock, &dsock) < 0)
+	if (NgMkSockNode(name, &csock, &dsock) < 0) {
+		if (errno == EPROTONOSUPPORT) {
+			if (kldload(NG_SOCKET_KLD) < 0)
+				err(EX_OSERR, "can't load %s", NG_SOCKET_KLD);
+			if (NgMkSockNode(name, &csock, &dsock) >= 0)
+				goto gotNode;
+		}
 		err(EX_OSERR, "can't create node");
+	}
+gotNode:
 
 	/* Do commands as requested */
 	if (ac == 0) {

usr.sbin/ngctl/ngctl.8

@@ -60,6 +60,12 @@ will enter interactive mode. Otherwise
 .Nm ngctl
 will execute the supplied command(s) and exit immediately.
 .Pp
+If the
+.Dv ng_socket.ko
+module is not installed in the kernel,
+.Nm ngctl
+will attempt to install it.
+.Pp
 The options are as follows:
 .Bl -tag -width indent
 .It Fl f Ar nodeinfo

usr.sbin/ngctl/ngctl.h

@@ -38,9 +38,11 @@
  */
 
 #include <sys/types.h>
+#include <sys/param.h>
 #include <sys/time.h>
 #include <sys/socket.h>
 #include <sys/select.h>
+#include <sys/linker.h>
 
 #include <stdio.h>
 #include <stdlib.h>