nixos/hardware/gpgSmartcard: init udev rules

nixos/modules/hardware/gpgsmartcards.nix

@@ -0,0 +1,37 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+let
+  # gnupg's manual describes how to setup ccid udev rules:
+  #   https://www.gnupg.org/howtos/card-howto/en/ch02s03.html
+  # gnupg folks advised me (https://dev.gnupg.org/T5409) to look at debian's rules:
+  # https://salsa.debian.org/debian/gnupg2/-/blob/debian/main/debian/scdaemon.udev
+
+  # the latest rev of the entire debian gnupg2 repo as of 2021-04-28
+  # the scdaemon.udev file was last commited on 2021-01-05 (7817a03):
+  scdaemonUdevRev = "01898735a015541e3ffb43c7245ac1e612f40836";
+
+  scdaemonRules = pkgs.fetchurl {
+    url = "https://salsa.debian.org/debian/gnupg2/-/raw/${scdaemonUdevRev}/debian/scdaemon.udev";
+    sha256 = "08v0vp6950bz7galvc92zdss89y9vcwbinmbfcdldy8x72w6rqr3";
+  };
+
+  # per debian's udev deb hook (https://man7.org/linux/man-pages/man1/dh_installudev.1.html)
+  destination = "60-scdaemon.rules";
+
+  scdaemonUdevRulesPkg = pkgs.runCommandNoCC "scdaemon-udev-rules" {} ''
+    loc="$out/lib/udev/rules.d/"
+    mkdir -p "''${loc}"
+    cp "${scdaemonRules}" "''${loc}/${destination}"
+  '';
+
+  cfg = config.hardware.gpgSmartcards;
+in {
+  options.hardware.gpgSmartcards = {
+    enable = mkEnableOption "udev rules for gnupg smart cards";
+  };
+
+  config = mkIf cfg.enable {
+    services.udev.packages = [ scdaemonUdevRulesPkg ];
+  };
+}

nixos/modules/module-list.nix

@@ -50,6 +50,7 @@
   ./hardware/device-tree.nix
   ./hardware/gkraken.nix
   ./hardware/flirc.nix
+  ./hardware/gpgsmartcards.nix
   ./hardware/i2c.nix
   ./hardware/sensor/hddtemp.nix
   ./hardware/sensor/iio.nix