add s6-rc-up-tree: start reverse deps of controlled service

When s6-rc stops a service, it also stops everything that
depends on it. but when it starts a service it starts only
that service, so we have to go through the other services
depending on it and figure out if they should be started too.

pkgs/s6-rc-up-tree/s6-rc-up-tree.sh

@@ -0,0 +1,24 @@
+service=$1
+
+blocks=""
+for controlled in $(cd /run/services/controlled/ && echo *); do
+    down=$(s6-rc -un0 change $controlled)
+    echo $controlled $down
+    if test -n "$down"; then
+	blocks="$blocks $controlled "
+    fi
+done
+
+for s in $(s6-rc-db -d all-dependencies $service); do
+    for dep in $(s6-rc-db all-dependencies $s); do
+	case "$blocks" in
+	    "* $dep *")
+		echo "not starting $s, blocked by $dep"
+		;;
+	    *)
+		echo "starting $s because $service"
+		s6-rc -u change $s
+		;;
+	esac
+    done
+done