tools/hotplug: add helper script to visualize systemd dependencies

A small helper to draw a graph with dot(1) and show it with display(1):
bash tools/hotplug/Linux/systemd/show_service_dependencies.sh \
	tools/hotplug/Linux/systemd/*.in

A red line means Requires= aka "enable it"
A blue line means After=
A green line means Before=

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Wei Liu <wei.liu2@citrix.com>

tools/hotplug/Linux/systemd/show_service_dependencies.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+# dot(1) from graphviz, display(1) from ImageMagick
+# Usage: bash $0 tools/hotplug/Linux/systemd/*.in
+(
+echo " digraph systemd {"
+for file in "$@"
+do
+	if test -f "$file"
+	then
+		unit=${file##*/}
+		unit=${unit%.in}
+		requires="`grep ^Requires= $file | cut -f 2- -d =`"
+		before="`grep ^Before= $file | cut -f 2- -d =`"
+		after="`grep ^After= $file | cut -f 2- -d =`"
+		echo "\"$unit\" [fillcolor=lightgray color=black fontcolor=black style=filled];"
+		for i in $requires
+		do
+			echo "\"$i\" -> \"$unit\" [color=red];"
+		done
+		for i in $after
+		do
+			echo "\"$i\" -> \"$unit\" [color=blue];"
+		done
+		for i in $before
+		do
+			echo "\"$unit\" -> \"$i\" [color=green];"
+		done
+	fi
+done
+echo "}"
+) | dot -Tpng | display -