customize: add a "touch" operation (RHBZ#1212808)

builder/cmdline.ml

@@ -312,7 +312,8 @@ read the man page virt-builder(1).
           | `Password _ | `RootPassword _ | `Scrub _ | `SSHInject _
           | `Timezone _ | `Truncate _ | `TruncateRecursive _
           | `Upload _ | `Write _ | `Chmod _
-          | `CommandsFromFile _ | `CopyIn _ | `Copy _ | `Move _ -> false
+          | `CommandsFromFile _ | `CopyIn _ | `Copy _ | `Move _
+          | `Touch _ -> false
         ) ops.ops in
         if requires_execute_on_guest then
           error (f_"sorry, cannot run commands on a guest with a different architecture");

customize/customize_run.ml

@@ -268,6 +268,10 @@ exec >>%s 2>&1
       if not (Timezone.set_timezone g root tz) then
         warning (f_"timezone could not be set for this type of guest")
 
+    | `Touch path ->
+      msg (f_"Running touch: %s") path;
+      g#touch path
+
     | `Update ->
       msg (f_"Updating core packages");
       let cmd = guest_update_command () in

generator/customize.ml

@@ -363,6 +363,14 @@ Set the default timezone of the guest to C<TIMEZONE>.  Use a location
 string like C<Europe/London>";
   };
 
+  { op_name = "touch";
+    op_type = String "FILE";
+    op_discrim = "`Touch";
+    op_shortdesc = "Run touch on a file";
+    op_pod_longdesc = "\
+This command performs a L<touch(1)>-like operation on C<FILE>.";
+  };
+
   { op_name = "update";
     op_type = Unit;
     op_discrim = "`Update";