nixos/libvirtd: add support for nixos managed libvirt hooks

Libvirt support calling user defined hooks on certains events.
Documentation can be found https://libvirt.org/hooks.html.
This commit allow specifying these hooks via the
virtualisation.libvirtd.hooks.<name>.* options

nixos/modules/virtualisation/libvirtd.nix

@@ -129,6 +129,60 @@ let
       };
     };
   };
+
+  hooksModule = types.submodule {
+    options = {
+      daemon = mkOption {
+        type = types.attrsOf types.path;
+        default = { };
+        description = lib.mdDoc ''
+          Hooks that will be placed under /var/lib/libvirt/hooks/daemon.d/
+          and called for daemon start/shutdown/SIGHUP events.
+          Please see https://libvirt.org/hooks.html for documentation.
+        '';
+      };
+
+      qemu = mkOption {
+        type = types.attrsOf types.path;
+        default = { };
+        description = lib.mdDoc ''
+          Hooks that will be placed under /var/lib/libvirt/hooks/qemu.d/
+          and called for qemu domains begin/end/migrate events.
+          Please see https://libvirt.org/hooks.html for documentation.
+        '';
+      };
+
+      lxc = mkOption {
+        type = types.attrsOf types.path;
+        default = { };
+        description = lib.mdDoc ''
+          Hooks that will be placed under /var/lib/libvirt/hooks/lxc.d/
+          and called for lxc domains begin/end events.
+          Please see https://libvirt.org/hooks.html for documentation.
+        '';
+      };
+
+      libxl = mkOption {
+        type = types.attrsOf types.path;
+        default = { };
+        description = lib.mdDoc ''
+          Hooks that will be placed under /var/lib/libvirt/hooks/libxl.d/
+          and called for libxl-handled xen domains begin/end events.
+          Please see https://libvirt.org/hooks.html for documentation.
+        '';
+      };
+
+      network = mkOption {
+        type = types.attrsOf types.path;
+        default = { };
+        description = lib.mdDoc ''
+          Hooks that will be placed under /var/lib/libvirt/hooks/lxc.d/
+          and called for networks begin/end events.
+          Please see https://libvirt.org/hooks.html for documentation.
+        '';
+      };
+    };
+  };
 in
 {
 
@@ -246,6 +300,14 @@ in
         QEMU related options.
       '';
     };
+
+    hooks = mkOption {
+      type = hooksModule;
+      default = { };
+      description = lib.mdDoc ''
+        Hooks related options.
+      '';
+    };
   };
 
 
@@ -335,6 +397,15 @@ in
           ln -s --force ${ovmfpackage}/FV/AAVMF_VARS.fd /run/${dirName}/nix-ovmf/
           ln -s --force ${ovmfpackage}/FV/OVMF_VARS.fd /run/${dirName}/nix-ovmf/
         '')}
+
+        # Symlink hooks to /var/lib/libvirt
+        ${concatStringsSep "\n" (map (driver:
+          ''
+          mkdir -p /var/lib/${dirName}/hooks/${driver}.d
+          rm -rf /var/lib/${dirName}/hooks/${driver}.d/*
+          ${concatStringsSep "\n" (mapAttrsToList (name: value:
+            "ln -s --force ${value} /var/lib/${dirName}/hooks/${driver}.d/${name}") cfg.hooks.${driver})}
+        '') (attrNames cfg.hooks))}
       '';
 
       serviceConfig = {

nixos/tests/libvirtd.nix

@@ -11,6 +11,9 @@ import ./make-test-python.nix ({ pkgs, ... }: {
           memorySize = 2048;
 
           libvirtd.enable = true;
+          libvirtd.hooks.qemu.is_working = "${pkgs.writeShellScript "testHook.sh" ''
+            touch /tmp/qemu_hook_is_working
+          ''}";
         };
         boot.supportedFilesystems = [ "zfs" ];
         networking.hostId = "deadbeef"; # needed for zfs
@@ -57,5 +60,9 @@ import ./make-test-python.nix ({ pkgs, ... }: {
       virthost.shutdown()
       virthost.wait_for_unit("multi-user.target")
       virthost.wait_until_succeeds("ping -c 1 nixos")
+
+    with subtest("test if hooks are linked and run"):
+      virthost.succeed("ls /var/lib/libvirt/hooks/qemu.d/is_working")
+      virthost.succeed("ls /tmp/qemu_hook_is_working")
   '';
 })