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.

modules/s6/default.nix

@@ -8,7 +8,7 @@ let
     stdenvNoCC;
   inherit (lib.lists) unique concatMap;
   inherit (pkgs.pseudofile) dir symlink;
-  inherit (pkgs.liminix.services) bundle;
+  inherit (pkgs.liminix.services) oneshot bundle;
 
   s6-rc-db =
     let
@@ -31,12 +31,25 @@ let
         isControlled s ||
         (lib.lists.any isDependentOnControlled s.dependencies);
 
+      # all controlled services depend on this oneshot, which
+      # makes a list of them so we can identify them at runtime
+      controlled = oneshot {
+        name = "controlled";
+        up = ''
+          mkdir -p /run/services/controlled
+          for s in $(s6-rc-db -d dependencies controlled); do
+            touch /run/services/controlled/$s
+          done
+        '';
+        down = "rm -r /run/services/controlled";
+      };
+
       defaultStart =
         builtins.filter
           (s: !(isDependentOnControlled s)) allServices;
       defaultDefaultTarget = bundle {
         name = "default";
-        contents = defaultStart;
+        contents = defaultStart ++ [controlled];
       };
       servicesAttrs = {
         default = defaultDefaultTarget;

pkgs/default.nix

@@ -98,6 +98,7 @@ in {
   run-liminix-vm = callPackage ./run-liminix-vm {};
   s6-init-bin =  callPackage ./s6-init-bin {};
   s6-rc-database = callPackage ./s6-rc-database {};
+  s6-rc-up-tree = callPackage ./s6-rc-up-tree {};
 
   # schnapps is written by Turris and provides a high-level interface
   # to btrfs snapshots. It may be useful on the Turris Omnia to
@@ -112,6 +113,7 @@ in {
   uevent-watch = callPackage ./uevent-watch {};
   usb-modeswitch = callPackage ./usb-modeswitch {};
   writeAshScript = callPackage ./write-ash-script {};
+  writeAshScriptBin = callPackage ./write-ash-script/bin.nix {};
   writeFennel = callPackage ./write-fennel {};
   writeFennelScript = callPackage ./write-fennel-script {};
 }

pkgs/liminix-tools/services/builder.sh

@@ -16,6 +16,8 @@ done
 if test -n "$controller" ; then
     d=$(dirname $(cd ${controller} && ls -d */type))
     echo "$d)" > $out/${name}/controller
+    #       ^ why is there a closing paren here?
+    touch $out/${name}/dependencies.d/controlled
 fi
 
 for i in timeout-up timeout-down run notification-fd up down finish consumer-for producer-for pipeline-name restart-on-upgrade; do

pkgs/s6-rc-up-tree/default.nix

@@ -0,0 +1,4 @@
+{
+  writeAshScriptBin
+}:
+writeAshScriptBin "s6-rc-up-tree" {} (builtins.readFile ./s6-rc-up-tree.sh)

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

pkgs/s6-rc-up-tree/test-list

@@ -0,0 +1,7 @@
+
+the service starts
+uncontrolled descendants start
+controlled descendants don't start
+descendants which depend on a _different_ controlled service, which is down, don't start
+descendants which depend on a _different_ controlled service, which is up, do start
+

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]