[PATCH v2 3/8] oxenstored: add a --use-select command line flag

[Zheng Li <dev@zheng.li>]

This allows to fall back to the original Unix.select if preferred. It could be
useful for debugging purposes too.

Signed-off-by: Zheng Li <dev@zheng.li>
---
 tools/ocaml/xenstored/parse_arg.ml |  8 ++++++--
 tools/ocaml/xenstored/select.ml    | 15 ++++++++++++++-
 tools/ocaml/xenstored/select.mli   |  9 ++++++++-
 tools/ocaml/xenstored/xenstored.ml |  2 ++
 4 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/tools/ocaml/xenstored/parse_arg.ml b/tools/ocaml/xenstored/parse_arg.ml
index 5d21601..6e22c16 100644
--- a/tools/ocaml/xenstored/parse_arg.ml
+++ b/tools/ocaml/xenstored/parse_arg.ml
@@ -25,6 +25,7 @@ type config =
 	tracefile: string option; (* old xenstored compatibility *)
 	restart: bool;
 	disable_socket: bool;
+	use_select: bool;
 }
 
 let do_argv =
@@ -35,7 +36,8 @@ let do_argv =
 	and reraise_top_level = ref false
 	and config_file = ref ""
 	and restart = ref false
-	and disable_socket = ref false in
+	and disable_socket = ref false
+	and use_select = ref false in
 
 	let speclist =
 		[ ("--no-domain-init", Arg.Unit (fun () -> domain_init := false),
@@ -52,8 +54,9 @@ let do_argv =
 		  ("-T", Arg.Set_string tracefile, ""); (* for compatibility *)
 		  ("--restart", Arg.Set restart, "Read database on starting");
 		  ("--disable-socket", Arg.Unit (fun () -> disable_socket := true), "Disable socket");
+		  ("--use-select", Arg.Unit (fun () -> use_select := true), "Use select instead of poll"); (* for backward compatibility and testing *)
 		] in
-	let usage_msg = "usage : xenstored [--config-file <filename>] [--no-domain-init] [--help] [--no-fork] [--reraise-top-level] [--restart] [--disable-socket]" in
+	let usage_msg = "usage : xenstored [--config-file <filename>] [--no-domain-init] [--help] [--no-fork] [--reraise-top-level] [--restart] [--disable-socket] [--use-select]" in
 	Arg.parse speclist (fun s -> ()) usage_msg;
 	{
 		domain_init = !domain_init;
@@ -65,4 +68,5 @@ let do_argv =
 		tracefile = if !tracefile <> "" then Some !tracefile else None;
 		restart = !restart;
 		disable_socket = !disable_socket;
+		use_select = !use_select;
 	}
diff --git a/tools/ocaml/xenstored/select.ml b/tools/ocaml/xenstored/select.ml
index ab8c847..0455e16 100644
--- a/tools/ocaml/xenstored/select.ml
+++ b/tools/ocaml/xenstored/select.ml
@@ -36,7 +36,7 @@ let get_sys_fs_nr_open () =
 
 let init_event () = {read = false; write = false; except = false}
 
-let select in_fds out_fds exc_fds timeout =
+let poll_select in_fds out_fds exc_fds timeout =
 	let h = Hashtbl.create 57 in
 	let add_event event_set fd =
 		let e =
@@ -62,3 +62,16 @@ let select in_fds out_fds exc_fds timeout =
 			 (if event.write then fd :: w else w),
 			 (if event.except then fd :: x else x))
 			a r
+
+(* If the use_poll function is not called at all, we default to the original Unix.select behavior *)
+let select_fun = ref Unix.select
+
+let use_poll yes =
+	let sel_fun, max_fd =
+		if yes then poll_select, get_sys_fs_nr_open ()
+		else Unix.select, 1024 in
+	select_fun := sel_fun;
+	set_fd_limit max_fd
+
+let select in_fds out_fds exc_fds timeout =
+	(!select_fun) in_fds out_fds exc_fds timeout
diff --git a/tools/ocaml/xenstored/select.mli b/tools/ocaml/xenstored/select.mli
index 1253d4e..3912779 100644
--- a/tools/ocaml/xenstored/select.mli
+++ b/tools/ocaml/xenstored/select.mli
@@ -14,7 +14,14 @@
 
 
 (** Same interface and semantics as [Unix.select] but with an extra alternative
-    implementation based on poll. *)
+    implementation based on poll. Switching implementations is done by calling
+     the [use_poll] function. *)
 val select:
 	Unix.file_descr list -> Unix.file_descr list -> Unix.file_descr list -> float
 	-> Unix.file_descr list * Unix.file_descr list * Unix.file_descr list
+
+(** [use_poll true] will use poll based select with max fds number limitation
+   eliminated; [use_poll false] will use standard [Unix.select] with max fd
+   number set to 1024; not calling this function at all equals to use the
+   standard [Unix.select] with max fd number setting untouched. *)
+val use_poll: bool -> unit
diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index bfa488f..dacea21 100644
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -274,6 +274,8 @@ let _ =
 		);
 	);
 
+	Select.use_poll (not cf.use_select);
+
 	Sys.set_signal Sys.sighup (Sys.Signal_handle sighup_handler);
 	Sys.set_signal Sys.sigterm (Sys.Signal_handle (fun i -> quit := true));
 	Sys.set_signal Sys.sigusr1 (Sys.Signal_handle (fun i -> sigusr1_handler store));
-- 
2.1.0