Create paste directories in /ceph/p

Ensure that all hut users have a paste directory in /ceph/p owned by
themselves. We need to wait for the ceph mount point to create them, so
we use a systemd service that waits for the remote-fs.target.

Reviewed-by: Aleix Boné <abonerib@bsc.es>

m/hut/p.nix

@@ -1,4 +1,4 @@
-{ pkgs, ... }:
+{ pkgs, lib, config, ... }:
 let
   p = pkgs.writeShellScriptBin "p" ''
     set -e
@@ -21,4 +21,23 @@ let
 in
 {
   environment.systemPackages = with pkgs; [ p ];
+
+  # Make sure we have a directory per user. We cannot use the nice
+  # systemd-tmpfiles-setup.service service because this is a remote FS, and it
+  # may not be mounted when it runs.
+  systemd.services.create-paste-dirs = let
+    # Take only normal users in hut
+    users = lib.filterAttrs (_: v: v.isNormalUser) config.users.users;
+    commands = lib.concatLists (lib.mapAttrsToList
+      (_: user: [
+        "install -d -o ${user.name} -g ${user.group} -m 0755 /ceph/p/${user.name}"
+      ]) users);
+    script = pkgs.writeShellScript "create-paste-dirs.sh" (lib.concatLines commands);
+  in {
+    enable = true;
+    wants = [ "remote-fs.target" ];
+    after = [ "remote-fs.target" ];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig.ExecStart = script;
+  };
 }