--- zfs.orig	2018-10-19 13:42:38.188027000 +0200
+++ zfs	2019-05-17 19:41:07.712859000 +0200
@@ -16,6 +16,23 @@
 stop_cmd="zfs_stop"
 required_modules="zfs"
 
+#
+# Add the following lines to /etc/rc.conf to enable ZFS ordered mount:
+# zfs_ordered_mount_enable (bool):                Mount ZFS in order (or NO).
+# zfs_ordered_mount_zpools (str):                 Ordered list of all zpools to mount.
+# zfs_ordered_mount_zpoolname_egrep_filter (str): Optional egrep(1) pattern for filtering unwanted filesystems, one per zpool.
+#                                                 Filesystems having canmount=off will be excluded automatically.
+#
+# Example:
+# zfs_ordered_mount_enable="YES"
+# zfs_ordered_mount_zpools="zroot zdata"
+# zfs_ordered_mount_zroot_egrep_filter="zroot\$|zroot/ROOT|zroot/do-not-destroy"
+# zfs_ordered_mount_zdata_egrep_filter="zdata\$|zdata/do-not-destroy"
+#
+
+zfs_ordered_mount_enable=${zfs_ordered_mount_enable:-"NO"}
+zfs_ordered_mount_zpools=${zfs_ordered_mount_zpools:-""}
+
 zfs_start_jail()
 {
 	if [ `$SYSCTL_N security.jail.mount_allowed` -eq 1 ]; then
@@ -25,7 +42,28 @@
 
 zfs_start_main()
 {
-	zfs mount -va
+	if checkyesno zfs_ordered_mount_enable; then
+		if [ -z "${zfs_ordered_mount_zpools}" ]; then
+			# Save those who forgot to list their zpools.
+			echo $0: missing value for zfs_ordered_mount_zpools, check /etc/rc.conf
+			zfs mount -av
+		else
+			local _zpool _egrep_filter_name _egrep_filter _fs
+			for _zpool in ${zfs_ordered_mount_zpools}; do
+				_egrep_filter_name=zfs_ordered_mount_${_zpool}_egrep_filter
+				_egrep_filter=`eval echo \$\{${_egrep_filter_name}\}`
+				if [ -n "${_egrep_filter}" ]; then
+					# Need to separate our ^off from the user's specification.
+					_egrep_filter="|${_egrep_filter}"
+				fi
+				for _fs in `zfs list -Hro canmount,name -t filesystem ${_zpool} | egrep -ve "^off${_egrep_filter}" | awk '{print $2}'`; do
+					zfs mount -v ${_fs}
+				done
+			done
+		fi
+	else
+		zfs mount -va
+	fi
 	zfs share -a
 	if [ ! -r /etc/zfs/exports ]; then
 		touch /etc/zfs/exports