add ssh module

modules/ssh/ssh.nix

@@ -0,0 +1,42 @@
+{
+  liminix
+, dropbear
+, serviceFns
+, lib
+}:
+p :
+let
+  inherit (liminix.services) longrun;
+  inherit (lib) concatStringsSep;
+  options =
+    [
+      "-e" #  pass environment to child
+      "-E" #  log to stderr
+      "-R" #  create hostkeys if needed
+      "-P /run/dropbear.pid"
+      "-F" #  don't fork into background
+    ] ++
+    (lib.optional (! p.allowRoot) "-w") ++
+    (lib.optional (! p.allowPasswordLogin) "-s") ++
+    (lib.optional (! p.allowPasswordLoginForRoot) "-g") ++
+    (lib.optional (! p.allowLocalPortForward) "-j") ++
+    (lib.optional (! p.allowRemotePortForward) "-k") ++
+    (lib.optional (! p.allowRemoteConnectionToForwardedPorts) "-a") ++
+    [(if p.address != null
+      then "-p ${p.address}:${p.port}"
+      else "-p ${builtins.toString p.port}")] ++
+    [p.extraConfig];
+in
+longrun {
+  name = "sshd";
+  # env -i clears the environment so we don't pass anything weird to
+  # ssh sessions
+  run = ''
+    if test -d /persist; then
+      mkdir -p /persist/secrets/dropbear
+      ln -s /persist/secrets/dropbear /run
+    fi
+    . /etc/profile # sets PATH but do we need this?  it's the same file as ashrc
+    exec env -i ENV=/etc/ashrc PATH=$PATH ${dropbear}/bin/dropbear ${concatStringsSep " " options}
+  '';
+}