tools/oxenstored: validate config file before live update

The configuration file can contain typos or various errors that could prevent
live update from succeeding (e.g. a flag only valid on a different version).
Unknown entries in the config file would be ignored on startup normally,
add a strict --config-test that live-update can use to check that the config file
is valid *for the new binary*.

For compatibility with running old code during live update recognize
--live --help as an equivalent to --config-test.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
(cherry picked from commit e6f07052ce)

tools/ocaml/xenstored/parse_arg.ml

@@ -26,8 +26,14 @@ type config =
 	restart: bool;
 	live_reload: bool;
 	disable_socket: bool;
+	config_test: bool;
 }
 
+let get_config_filename config_file =
+	match config_file with
+	| Some name -> name
+	| None	    -> Define.default_config_dir ^ "/oxenstored.conf"
+
 let do_argv =
 	let pidfile = ref "" and tracefile = ref "" (* old xenstored compatibility *)
 	and domain_init = ref true
@@ -38,6 +44,8 @@ let do_argv =
 	and restart = ref false
 	and live_reload = ref false
 	and disable_socket = ref false
+	and config_test = ref false
+	and help = ref false
 	in
 
 	let speclist =
@@ -55,10 +63,27 @@ let do_argv =
 		  ("-T", Arg.Set_string tracefile, ""); (* for compatibility *)
 		  ("--restart", Arg.Set restart, "Read database on starting");
 		  ("--live", Arg.Set live_reload, "Read live dump on startup");
+		  ("--config-test", Arg.Set config_test, "Test validity of config file");
 		  ("--disable-socket", Arg.Unit (fun () -> disable_socket := true), "Disable socket");
+		  ("--help", Arg.Set help, "Display this list of options")
 		] in
 	let usage_msg = "usage : xenstored [--config-file <filename>] [--no-domain-init] [--help] [--no-fork] [--reraise-top-level] [--restart] [--disable-socket]" in
 	Arg.parse speclist (fun _ -> ()) usage_msg;
+	let () =
+		if !help then begin
+			if !live_reload then
+				(*
+				 * Transform --live --help into --config-test for backward compat with
+				 * running code during live update.
+				 * Caller will validate config and exit
+				 *)
+				config_test := true
+			else begin
+				Arg.usage_string speclist usage_msg |> print_endline;
+				exit 0
+			end
+		end
+	in
 	{
 		domain_init = !domain_init;
 		activate_access_log = !activate_access_log;
@@ -70,4 +95,5 @@ let do_argv =
 		restart = !restart;
 		live_reload = !live_reload;
 		disable_socket = !disable_socket;
+		config_test = !config_test;
 	}

tools/ocaml/xenstored/xenstored.ml

@@ -88,7 +88,7 @@ let default_pidfile = Paths.xen_run_dir ^ "/xenstored.pid"
 
 let ring_scan_interval = ref 20
 
-let parse_config filename =
+let parse_config ?(strict=false) filename =
 	let pidfile = ref default_pidfile in
 	let options = [
 		("merge-activate", Config.Set_bool Transaction.do_coalesce);
@@ -129,11 +129,12 @@ let parse_config filename =
 		("xenstored-port", Config.Set_string Domains.xenstored_port); ] in
 	begin try Config.read filename options (fun _ _ -> raise Not_found)
 	with
-	| Config.Error err -> List.iter (fun (k, e) ->
+	| Config.Error err as e -> List.iter (fun (k, e) ->
 		match e with
 		| "unknown key" -> eprintf "config: unknown key %s\n" k
 		| _             -> eprintf "config: %s: %s\n" k e
 		) err;
+		if strict then raise e
 	| Sys_error m -> eprintf "error: config: %s\n" m;
 	end;
 	!pidfile
@@ -358,6 +359,12 @@ let tweak_gc () =
 let () =
 	Printexc.set_uncaught_exception_handler Logging.fallback_exception_handler;
 	let cf = do_argv in
+	if cf.config_test then begin
+		let path = config_filename cf in
+		let _pidfile:string = parse_config ~strict:true path in
+		Printf.printf "Configuration valid at %s\n%!" path;
+		exit 0
+	end;
 	let pidfile =
 		if Sys.file_exists (config_filename cf) then
 			parse_config (config_filename cf)