Add Nix support

flake.nix

@@ -0,0 +1,62 @@
+{
+  description = "PTP daemon (PTPd) is an implementation the Precision Time Protocol (PTP) version
+2 as defined by 'IEEE Std 1588-2008'. PTP provides precise time coordination of
+Ethernet LAN connected computers. It was designed primarily for instrumentation
+and control systems.";
+
+  # Nixpkgs / NixOS version to use.
+  inputs.nixpkgs.url = "nixpkgs/nixos-21.05";
+
+  outputs = { self, nixpkgs }:
+    let
+      # Generate a user-friendly version number.
+      version = builtins.substring 0 8 self.lastModifiedDate;
+
+      # System types to support.
+      supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
+
+      # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
+      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+
+      # Nixpkgs instantiated for supported system types.
+      nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; overlays = [ self.overlay ]; });
+
+    in
+
+    {
+
+      # A Nixpkgs overlay.
+      overlay = final: prev: {
+
+        ptpd = with final; stdenv.mkDerivation rec {
+          name = "ptpd-${version}";
+
+          src = ./.;
+
+          nativeBuildInputs = [ autoreconfHook ];
+          buildInputs = [ libpcap ];
+        };
+
+      };
+
+      # Provide some binary packages for selected system types.
+      packages = forAllSystems (system:
+        {
+          inherit (nixpkgsFor.${system}) ptpd;
+        });
+
+      # The default package for 'nix build'. This makes sense if the
+      # flake provides only one package or there is a clear "main"
+      # package.
+      defaultPackage = forAllSystems (system: self.packages.${system}.ptpd);
+
+      # A NixOS module, if applicable (e.g. if the package provides a system service).
+      nixosModules.ptpd =
+        { pkgs, ... }:
+        {
+          nixpkgs.overlays = [ self.overlay ];
+          environment.systemPackages = [ pkgs.ptpd ];
+        };
+
+    };
+}