From beb6e260d4e071408026bf86f90afd7bb6493d3c Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Thu, 23 Mar 2023 12:48:10 +0000
Subject: [PATCH] PoC support for hardware watchdog

---
 devices/gl-ar750/default.nix |  4 ++++
 examples/arhcive.nix         | 38 ++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/devices/gl-ar750/default.nix b/devices/gl-ar750/default.nix
index f7d2272..9e4b2b6 100644
--- a/devices/gl-ar750/default.nix
+++ b/devices/gl-ar750/default.nix
@@ -186,6 +186,10 @@
           MTD = "y";
           MTD_CMDLINE_PARTS = "y";
           MTD_BLOCK = "y";          # fix undefined ref to register_mtd_blktrans_devs
+
+          WATCHDOG = "y";
+          ATH79_WDT = "y";  # watchdog timer
+
           CPU_BIG_ENDIAN= "y";
 
           # this is all copied from nixwrt ath79 config. Clearly not all
diff --git a/examples/arhcive.nix b/examples/arhcive.nix
index d44f93a..0550848 100644
--- a/examples/arhcive.nix
+++ b/examples/arhcive.nix
@@ -78,6 +78,43 @@ in rec {
     '';
   };
 
+  services.watchdog =
+    let
+      watched = with config.services ; [ sshd dhcpc ];
+      spinupGrace = 60;
+      script = pkgs.writeAshScript "gaspode" {
+        runtimeInputs = [ pkgs.s6 ];
+      } ''
+      deadline=$(expr $(date +%s) + ${toString spinupGrace})
+      services=$@
+      echo started feeding the dog
+      exec 3> ''${WATCHDOG-/dev/watchdog}
+
+      healthy(){
+          test $(date +%s) -le $deadline && return 0
+
+          for i in $services; do
+              if test "$(s6-svstat -o up /run/service/$i)" != "true" ; then
+                 echo "service $i is down"
+                 return 1
+              fi
+          done
+      }
+
+      while healthy ;do
+          sleep 10
+          echo >&3
+      done
+      echo "stopped feeding the dog"
+      sleep 6000  # don't want s6-rc to restart
+    '';
+    in longrun {
+      name = "watchdog";
+      run =
+        "${script} ${lib.concatStringsSep " " (builtins.map (s: s.name) watched)}";
+    };
+
+
   services.resolvconf = oneshot rec {
     dependencies = [ services.dhcpc ];
     name = "resolvconf";
@@ -174,6 +211,7 @@ in rec {
         resolvconf
         sshd
         rsync
+        watchdog
       ];
   };
   users.root.passwd = lib.mkForce secrets.root_password;