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

[Zheng Li <dev@xxxxxxxx>]

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@xxxxxxxx>
---
 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 c19df41..3e9ee68 100644
--- a/tools/ocaml/xenstored/select.ml
+++ b/tools/ocaml/xenstored/select.ml
@@ -38,7 +38,7 @@ 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


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