Index: usr.sbin/config/config.8
===================================================================
--- usr.sbin/config/config.8
+++ usr.sbin/config/config.8
@@ -39,6 +39,7 @@
 .Op Fl CVgp
 .Op Fl I Ar path
 .Op Fl d Ar destdir
+.Op Fl s Ar srcdir
 .Ar SYSTEM_NAME
 .Nm
 .Op Fl x Ar kernel
@@ -85,6 +86,10 @@
 does not append
 .Ar SYSTEM_NAME
 to the directory given.
+.It Fl s Ar srcdir
+Use
+.Ar srcdir
+as the source directory, instead of the default one.
 .It Fl m
 Print the MACHINE and MACHINE_ARCH values for this
 kernel and exit.
@@ -143,6 +148,14 @@
 definitions of
 the number of various devices that will be compiled into the system.
 .Pp
+The
+.Nm
+utility looks for kernel sources in the directory
+.Pa ../..
+or the one given with the
+.Fl s
+option.
+.Pp
 After running
 .Nm ,
 it is necessary to run
Index: usr.sbin/config/main.c
===================================================================
--- usr.sbin/config/main.c
+++ usr.sbin/config/main.c
@@ -116,7 +116,7 @@
 	printmachine = 0;
 	kernfile = NULL;
 	SLIST_INIT(&includepath);
-	while ((ch = getopt(argc, argv, "CI:d:gmpVx:")) != -1)
+	while ((ch = getopt(argc, argv, "CI:d:gmpsVx:")) != -1)
 		switch (ch) {
 		case 'C':
 			filebased = 1;
@@ -144,6 +144,12 @@
 		case 'p':
 			profiling++;
 			break;
+		case 's':
+			if (*srcdir == '\0')
+				strlcpy(srcdir, optarg, sizeof(srcdir));
+			else
+				errx(EXIT_FAILURE, "src directory already set");
+			break;
 		case 'V':
 			printf("%d\n", CONFIGVERS);
 			exit(0);
@@ -180,7 +186,8 @@
 		len = strlen(destdir);
 		while (len > 1 && destdir[len - 1] == '/')
 			destdir[--len] = '\0';
-		get_srcdir();
+		if (*srcdir == '\0')
+			get_srcdir();
 	} else {
 		strlcpy(destdir, CDIR, sizeof(destdir));
 		strlcat(destdir, PREFIX, sizeof(destdir));
@@ -275,7 +282,8 @@
 usage(void)
 {
 
-	fprintf(stderr, "usage: config [-CgmpV] [-d destdir] sysname\n");
+	fprintf(stderr,
+	    "usage: config [-CgmpV] [-d destdir] [-s srcdir] sysname\n");
 	fprintf(stderr, "       config -x kernel\n");
 	exit(EX_USAGE);
 }