freebsd-update: Add updatesready' and showconfig' commands

`freebsd-update updatesready' can be used to check if there are any pending
fetched updates that can be installed.

`freebsd-update showconfig' writes freebsd-update's configuration to
stdout.

This also changes the exit code of `freebsd-update install' to 2 in case
there are no updates pending to be installed and there wasn't a fetch phase
in the same invocation. This allows scripts to tell apart these error
conditions without breaking existing jail managers.

See freebsd-update(8) for details.

PR:		240757, 240177, 229346
Reviewed by:	manpages (bcr), sectam (emaste), yuripv
Differential Revision:	https://reviews.freebsd.org/D21473

usr.sbin/freebsd-update/freebsd-update.8

@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 14, 2017
+.Dd September 24, 2019
 .Dt FREEBSD-UPDATE 8
 .Os
 .Sh NAME
@@ -155,13 +155,24 @@ Note that this command may require up to 500 MB of space in
 depending on which components of the
 .Fx
 base system are installed.
+.It Cm updatesready
+Check if there are fetched updates ready to install.
+Returns exit code 2 if there are no updates to install.
 .It Cm install
 Install the most recently fetched updates or upgrade.
+Returns exit code 2 if there are no updates to install
+and the
+.Cm fetch
+command wasn't passed as an earlier argument in the same
+invocation.
 .It Cm rollback
 Uninstall the most recently installed updates.
 .It Cm IDS
 Compare the system against a "known good" index of the
 installed release.
+.It Cm showconfig
+Show configuration options after parsing conffile and command
+line options.
 .El
 .Sh TIPS
 .Bl -bullet

usr.sbin/freebsd-update/freebsd-update.sh

@@ -62,9 +62,11 @@ Commands:
   cron         -- Sleep rand(3600) seconds, fetch updates, and send an
                   email if updates were found
   upgrade      -- Fetch upgrades to FreeBSD version specified via -r option
+  updatesready -- Check if there are fetched updates ready to install
   install      -- Install downloaded updates or upgrades
   rollback     -- Uninstall most recently installed updates
   IDS          -- Compare the system against an index of "known good" files
+  showconfig   -- Show configuration
 EOF
 	exit 0
 }
@@ -503,7 +505,8 @@ parse_cmdline () {
 			;;
 
 		# Commands
-		cron | fetch | upgrade | install | rollback | IDS)
+		cron | fetch | upgrade | updatesready | install | rollback |\
+		IDS | showconfig)
 			COMMANDS="${COMMANDS} $1"
 			;;
 
@@ -827,7 +830,7 @@ install_check_params () {
 		echo "No updates are available to install."
 		if [ $ISFETCHED -eq 0 ]; then
 			echo "Run '$0 fetch' first."
-			exit 1
+			exit 2
 		fi
 		exit 0
 	fi
@@ -3333,6 +3336,21 @@ cmd_upgrade () {
 	upgrade_run || exit 1
 }
 
+# Check if there are fetched updates ready to install
+cmd_updatesready () {
+	# Construct a unique name from ${BASEDIR}
+	BDHASH=`echo ${BASEDIR} | sha256 -q`
+
+	# Check that we have updates ready to install
+	if ! [ -L ${BDHASH}-install ]; then
+		echo "No updates are available to install."
+		exit 2
+	fi
+
+	echo "There are updates available to install."
+	echo "Run '$0 install' to proceed."
+}
+
 # Install downloaded updates.
 cmd_install () {
 	install_check_params
@@ -3351,6 +3369,13 @@ cmd_IDS () {
 	IDS_run || exit 1
 }
 
+# Output configuration.
+cmd_showconfig () {
+	for X in ${CONFIGOPTIONS}; do
+		echo $X=$(eval echo \$${X})
+	done
+}
+
 #### Entry point
 
 # Make sure we find utilities from the base system