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*.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
---
 tools/ocaml/xenstored/parse_arg.ml | 4 ++++
 tools/ocaml/xenstored/process.ml   | 2 +-
 tools/ocaml/xenstored/xenstored.ml | 9 +++++++--
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/tools/ocaml/xenstored/parse_arg.ml b/tools/ocaml/xenstored/parse_arg.ml
index 965cb9ebeb..588970825f 100644
--- a/tools/ocaml/xenstored/parse_arg.ml
+++ b/tools/ocaml/xenstored/parse_arg.ml
@@ -26,6 +26,7 @@ type config =
 	restart: bool;
 	live_reload: bool;
 	disable_socket: bool;
+	config_test: bool;
 }
 
 let do_argv () =
@@ -38,6 +39,7 @@ let do_argv () =
 	and restart = ref false
 	and live_reload = ref false
 	and disable_socket = ref false
+	and config_test = ref false
 	in
 
 	let speclist =
@@ -55,6 +57,7 @@ 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");
 		] in
 	let usage_msg = "usage : xenstored [--config-file <filename>] [--no-domain-init] [--help] [--no-fork] [--reraise-top-level] [--restart] [--disable-socket]" in
@@ -70,4 +73,5 @@ let do_argv () =
 		restart = !restart;
 		live_reload = !live_reload;
 		disable_socket = !disable_socket;
+		config_test = !config_test;
 	}
diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index 27790d4a5c..d573c88685 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -121,7 +121,7 @@ let launch_exn t =
 
 let validate_exn t =
 	(* --help must be last to check validity of earlier arguments *)
-	let t' = {t with cmdline= t.cmdline @ ["--help"]} in
+	let t' = {t with cmdline= t.cmdline @ ["--config-test"]} in
 	let cmd = string_of_t t' in
 	debug "Executing %s" cmd ;
 	match Unix.fork () with
diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index 2aa0dbc0e1..34e706910e 100644
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/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);
@@ -126,11 +126,12 @@ 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
@@ -408,6 +409,10 @@ end
 
 let main () =
 	let cf = do_argv () in
+	if cf.config_test then begin
+	  let _pidfile:string = parse_config ~strict:true (config_filename cf) in
+	  exit 0
+	end;
 	let pidfile =
 		if Sys.file_exists (config_filename cf) then
 			parse_config (config_filename cf)
-- 
2.25.1