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/uevent-watch/default.nix

@@ -8,17 +8,21 @@
 , fennel
 , stdenv
 , fennelrepl
+, s6-rc-up-tree
+, makeWrapper
 }:
 stdenv.mkDerivation {
   name = "uevent-watch";
   src = ./.;
-  nativeBuildInputs = [ fennelrepl ];
+  nativeBuildInputs = [ fennelrepl makeWrapper ];
+  propagatedBuildInputs = [ s6-rc-up-tree ];
   installPhase = ''
     mkdir -p $out/bin
     cp -p ${writeFennel "uevent-watch" {
       packages = [fennel anoia nellie lualinux];
       mainFunction = "run";
     } ./watch.fnl} $out/bin/uevent-watch
+    wrapProgram $out/bin/uevent-watch --prefix PATH : "${s6-rc-up-tree}/bin"
   '';
   checkPhase = ''
     fennelrepl ./test.fnl

pkgs/uevent-watch/watch.fnl

@@ -18,7 +18,7 @@
 
 (fn start-service [devname linkname service]
   (match (if linkname (symlink (.. "/dev/" devname) linkname) true)
-    ok (pcall system (%% "s6-rc -b -u change %q" service))
+    ok (pcall system (%% "s6-rc-up-tree %q" service))
     (nil err) false))
 
 (fn stop-service [linkname service]