rc.d: Add precious_machine rc.conf knob to create /var/run/noshutdown

Reviewed by:	bapt, kevans, olce
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D50166

libexec/rc/rc.conf

@@ -29,6 +29,8 @@
 rc_info="NO"		# Enables display of informational messages at boot.
 rc_startmsgs="YES" 	# Show "Starting foo:" messages at boot
 rcshutdown_timeout="90" # Seconds to wait before terminating rc.shutdown
+precious_machine="NO"	# Set to YES to get some guards against mis-directed
+                        # shutdown(8) commands
 early_late_divider="FILESYSTEMS"	# Script that separates early/late
 			# stages of the boot process.  Make sure you know
 			# the ramifications if you change this.

libexec/rc/rc.d/Makefile

@@ -51,6 +51,7 @@ CONFS=	DAEMON \
 	netif \
 	netoptions \
 	netwait \
+	noshutdown \
 	${_nscd} \
 	${_opensm} \
 	os-release \

libexec/rc/rc.d/noshutdown

@@ -0,0 +1,31 @@
+#!/bin/sh
+#
+#
+
+# PROVIDE: noshutdown
+# REQUIRE: var
+# BEFORE:  LOGIN
+
+. /etc/rc.subr
+
+name="noshutdown"
+desc="Disable shutdown(8) for precious machines"
+rcvar="precious_machine"
+start_cmd="noshutdown_start"
+stop_cmd="noshutdown_stop"
+
+: ${noshutdown_file:="/var/run/noshutdown"}
+
+noshutdown_start()
+{
+	touch $noshutdown_file
+}
+
+noshutdown_stop()
+{
+	rm -f $noshutdown_file
+}
+
+load_rc_config $name
+
+run_rc_command "$1"