tools/ocaml/xenstored: fix live update exception

During live update we will load the /tool/xenstored path from the previous binary,
and then try to mkdir /tool again which will fail with EEXIST.
Check for existence of the path before creating it.

The write call to /tool/xenstored should not need any changes
(and we do want to overwrite any previous path, in case it changed).

Prior to 7110192 live update would work only if the binary path was
specified, and with 7110192 and this live update also works when
no binary path is specified in `xenstore-control live-update`.

Fixes: 7110192 ("tools/oxenstored: Fix Oxenstored Live Update")
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>

tools/ocaml/xenstored/xenstored.ml

@@ -353,7 +353,9 @@ let _ =
 	) in
 
 	(* required for xenstore-control to detect availability of live-update *)
-	Store.mkdir store Perms.Connection.full_rights (Store.Path.of_string "/tool");
+	let tool_path = Store.Path.of_string "/tool" in
+	if not (Store.path_exists store tool_path) then
+		Store.mkdir store Perms.Connection.full_rights tool_path;
 	Store.write store Perms.Connection.full_rights
 		(Store.Path.of_string "/tool/xenstored") Sys.executable_name;