freebsd-update: create a ZFS boot environment on install

Updated freebsd-update to allow it to create boot environments using
bectl should the system support it. The bectl utility was updated in
r352211 (490e13c) to support a 'check' to determine if the system
supports boot environments.  If UFS is used, the bectl check will fail
then no attempt will be made to create the boot environment.

If freebsd-update is run inside a jail, no attempt will be made to
create a boot environment.

The boot environment function will create a new environment using the
format: current FreeBSD kernel version and date/timestamp, example:

12.0-RELEASE-p10_2019-10-03_185233

This functionality can be disabled by setting 'CreateBootEnv' in
freebsd-update.conf to 'no'.

(cherry picked from commit f28f138)

usr.sbin/freebsd-update/freebsd-update.conf

@@ -74,3 +74,6 @@ MergeChanges /etc/ /boot/device.hints
 
 # When backing up a kernel also back up debug symbol files?
 # BackupKernelSymbolFiles no
+
+# Create a new boot environment when installing patches
+# CreateBootEnv yes

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

@@ -410,6 +410,23 @@ config_BackupKernelSymbolFiles () {
 	fi
 }
 
+config_CreateBootEnv () {
+	if [ -z ${BOOTENV} ]; then
+		case $1 in
+		[Yy][Ee][Ss])
+			BOOTENV=yes
+			;;
+		[Nn][Oo])
+			BOOTENV=no
+			;;
+		*)
+			return 1
+			;;
+		esac
+	else
+		return 1
+	fi
+}
 # Handle one line of configuration
 configline () {
 	if [ $# -eq 0 ]; then
@@ -586,6 +603,7 @@ default_params () {
 	config_BackupKernel yes
 	config_BackupKernelDir /boot/kernel.old
 	config_BackupKernelSymbolFiles no
+	config_CreateBootEnv yes
 
 	# Merge these defaults into the earlier-configured settings
 	mergeconfig
@@ -850,6 +868,44 @@ install_check_params () {
 	fi
 }
 
+# Creates a new boot environment
+install_create_be () {
+	# Figure out if we're running in a jail and return if we are
+	if [ `sysctl -n security.jail.jailed` = 1 ]; then
+	    return 1
+	fi
+	# Create a boot environment if enabled
+	if [ ${BOOTENV} = yes ]; then
+		bectl check 2>/dev/null
+		case $? in
+			0)
+				# Boot environment are supported
+				CREATEBE=yes
+				;;
+			255)
+				# Boot environments are not supported
+				CREATEBE=no
+				;;
+			*)
+				# If bectl returns an unexpected exit code, don't create a BE
+				CREATEBE=no
+				;;
+		esac
+		if [ ${CREATEBE} = yes ]; then
+			echo -n "Creating snapshot of existing boot environment... "
+			VERSION=`freebsd-version -k`
+			TIMESTAMP=`date +"%Y-%m-%d_%H%M%S"`
+			bectl create ${VERSION}_${TIMESTAMP}
+			if [ $? -eq 0 ]; then
+				echo "done.";
+			else
+				echo "failed."
+				exit 1
+			fi
+		fi
+	fi
+}
+
 # Perform sanity checks and set some final parameters in
 # preparation for UNinstalling updates.
 rollback_check_params () {
@@ -3366,6 +3422,7 @@ cmd_updatesready () {
 cmd_install () {
 	finalize_components_config ${COMPONENTS}
 	install_check_params
+	install_create_be
 	install_run || exit 1
 }