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[Xen-devel] [PATCH v7 3/9] libxl: ocaml: event management



Having bindings to the low-level functions libxl_osevent_register_hooks and
related, allows to run an event loop in OCaml; either one we write ourselves,
or one that is available elsewhere.

The Lwt cooperative threads library (http://ocsigen.org/lwt/), which is quite
popular these days, has an event loop that can be easily extended to poll any
additional fds that we get from libxl. Lwt provides a "lightweight" threading
model, which does not let you run any other (POSIX) threads in your
application, and therefore excludes an event loop implemented in the C
bindings.

Signed-off-by: Rob Hoes <rob.hoes@xxxxxxxxxx>
Acked-by: David Scott <dave.scott@xxxxxxxxxxxxx>

---
v7: Added comment in source to explain the unregistering of for_callback.
---
 tools/ocaml/libs/xl/xenlight.ml.in   |   37 ++++
 tools/ocaml/libs/xl/xenlight.mli.in  |   38 ++++
 tools/ocaml/libs/xl/xenlight_stubs.c |  354 ++++++++++++++++++++++++++++++++++
 3 files changed, 429 insertions(+)

diff --git a/tools/ocaml/libs/xl/xenlight.ml.in 
b/tools/ocaml/libs/xl/xenlight.ml.in
index a281425..46106b5 100644
--- a/tools/ocaml/libs/xl/xenlight.ml.in
+++ b/tools/ocaml/libs/xl/xenlight.ml.in
@@ -25,10 +25,47 @@ external ctx_alloc: Xentoollog.handle -> ctx = 
"stub_libxl_ctx_alloc"
 
 external test_raise_exception: unit -> unit = "stub_raise_exception"
 
+type event =
+       | POLLIN (* There is data to read *)
+       | POLLPRI (* There is urgent data to read *)
+       | POLLOUT (* Writing now will not block *)
+       | POLLERR (* Error condition (revents only) *)
+       | POLLHUP (* Device has been disconnected (revents only) *)
+       | POLLNVAL (* Invalid request: fd not open (revents only). *)
+
 external send_trigger : ctx -> domid -> trigger -> int -> unit = 
"stub_xl_send_trigger"
 external send_sysrq : ctx -> domid -> char -> unit = "stub_xl_send_sysrq"
 external send_debug_keys : ctx -> string -> unit = "stub_xl_send_debug_keys"
 
+module Async = struct
+       type for_libxl
+       type event_hooks
+       type osevent_hooks
+
+       external osevent_register_hooks' : ctx -> 'a -> osevent_hooks = 
"stub_libxl_osevent_register_hooks"
+       external osevent_occurred_fd : ctx -> for_libxl -> Unix.file_descr -> 
event list -> event list -> unit = "stub_libxl_osevent_occurred_fd"
+       external osevent_occurred_timeout : ctx -> for_libxl -> unit = 
"stub_libxl_osevent_occurred_timeout"
+
+       let osevent_register_hooks ctx ~user ~fd_register ~fd_modify 
~fd_deregister ~timeout_register ~timeout_modify =
+               Callback.register "libxl_fd_register" fd_register;
+               Callback.register "libxl_fd_modify" fd_modify;
+               Callback.register "libxl_fd_deregister" fd_deregister;
+               Callback.register "libxl_timeout_register" timeout_register;
+               Callback.register "libxl_timeout_modify" timeout_modify;
+               osevent_register_hooks' ctx user
+
+       let async_register_callback ~async_callback =
+               Callback.register "libxl_async_callback" async_callback
+
+       external evenable_domain_death : ctx -> domid -> int -> unit = 
"stub_libxl_evenable_domain_death"
+       external event_register_callbacks' : ctx -> 'a -> event_hooks = 
"stub_libxl_event_register_callbacks"
+
+       let event_register_callbacks ctx ~user ~event_occurs_callback 
~event_disaster_callback =
+               Callback.register "libxl_event_occurs_callback" 
event_occurs_callback;
+               Callback.register "libxl_event_disaster_callback" 
event_disaster_callback;
+               event_register_callbacks' ctx user
+end
+
 let register_exceptions () =
        Callback.register_exception "Xenlight.Error" (Error(ERROR_FAIL, ""))
 
diff --git a/tools/ocaml/libs/xl/xenlight.mli.in 
b/tools/ocaml/libs/xl/xenlight.mli.in
index d663196..170e0e0 100644
--- a/tools/ocaml/libs/xl/xenlight.mli.in
+++ b/tools/ocaml/libs/xl/xenlight.mli.in
@@ -27,7 +27,45 @@ external ctx_alloc: Xentoollog.handle -> ctx = 
"stub_libxl_ctx_alloc"
 
 external test_raise_exception: unit -> unit = "stub_raise_exception"
 
+type event =
+       | POLLIN (* There is data to read *)
+       | POLLPRI (* There is urgent data to read *)
+       | POLLOUT (* Writing now will not block *)
+       | POLLERR (* Error condition (revents only) *)
+       | POLLHUP (* Device has been disconnected (revents only) *)
+       | POLLNVAL (* Invalid request: fd not open (revents only). *)
+
 external send_trigger : ctx -> domid -> trigger -> int -> unit = 
"stub_xl_send_trigger"
 external send_sysrq : ctx -> domid -> char -> unit = "stub_xl_send_sysrq"
 external send_debug_keys : ctx -> string -> unit = "stub_xl_send_debug_keys"
 
+module Async : sig
+       type for_libxl
+       type event_hooks
+       type osevent_hooks
+
+       val osevent_register_hooks : ctx ->
+               user:'a ->
+               fd_register:('a -> Unix.file_descr -> event list -> for_libxl 
-> unit) ->
+               fd_modify:('a -> Unix.file_descr -> event list -> unit) ->
+               fd_deregister:('a -> Unix.file_descr -> unit) ->
+               timeout_register:('a -> int -> int -> for_libxl -> unit) ->
+               timeout_modify:('a -> unit) ->
+               osevent_hooks
+
+       external osevent_occurred_fd : ctx -> for_libxl -> Unix.file_descr -> 
event list -> event list -> unit = "stub_libxl_osevent_occurred_fd"
+       external osevent_occurred_timeout : ctx -> for_libxl -> unit = 
"stub_libxl_osevent_occurred_timeout"
+
+       val async_register_callback :
+               async_callback:(result:error option -> user:'a -> unit) ->
+               unit
+
+       external evenable_domain_death : ctx -> domid -> int -> unit = 
"stub_libxl_evenable_domain_death"
+
+       val event_register_callbacks : ctx ->
+               user:'a ->
+               event_occurs_callback:('a -> Event.t -> unit) ->
+               event_disaster_callback:('a -> event_type -> string -> int -> 
unit) ->
+               event_hooks
+end
+
diff --git a/tools/ocaml/libs/xl/xenlight_stubs.c 
b/tools/ocaml/libs/xl/xenlight_stubs.c
index 4ea2047..39a9632 100644
--- a/tools/ocaml/libs/xl/xenlight_stubs.c
+++ b/tools/ocaml/libs/xl/xenlight_stubs.c
@@ -30,6 +30,8 @@
 #include <libxl.h>
 #include <libxl_utils.h>
 
+#include <unistd.h>
+
 #include "caml_xentoollog.h"
 
 #define Ctx_val(x)(*((libxl_ctx **) Data_custom_val(x)))
@@ -370,6 +372,35 @@ static char *String_option_val(value v)
 
 #include "_libxl_types.inc"
 
+void async_callback(libxl_ctx *ctx, int rc, void *for_callback)
+{
+       CAMLparam0();
+       CAMLlocal2(error, tmp);
+       static value *func = NULL;
+       value *p = (value *) for_callback;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_async_callback");
+       }
+
+       if (rc == 0)
+               error = Val_none;
+       else {
+               tmp = Val_error(rc);
+               error = Val_some(tmp);
+       }
+
+       /* for_callback is a pointer to a "value" that was malloc'ed and
+        * registered with the OCaml GC. The value is handed back to OCaml
+        * in the following callback, after which the pointer is unregistered
+        * and freed. */
+       caml_callback2(*func, error, *p);
+
+       caml_remove_global_root(p);
+       free(p);
+}
+
 #define _STRINGIFY(x) #x
 #define STRINGIFY(x) _STRINGIFY(x)
 
@@ -703,6 +734,329 @@ value stub_xl_send_debug_keys(value ctx, value keys)
        CAMLreturn(Val_unit);
 }
 
+
+/* Event handling */
+
+short Poll_val(value event)
+{
+       CAMLparam1(event);
+       short res = -1;
+
+       switch (Int_val(event)) {
+               case 0: res = POLLIN; break;
+               case 1: res = POLLPRI; break;
+               case 2: res = POLLOUT; break;
+               case 3: res = POLLERR; break;
+               case 4: res = POLLHUP; break;
+               case 5: res = POLLNVAL; break;
+       }
+
+       CAMLreturn(res);
+}
+
+short Poll_events_val(value event_list)
+{
+       CAMLparam1(event_list);
+       short events = 0;
+
+       while (event_list != Val_emptylist) {
+               events |= Poll_val(Field(event_list, 0));
+               event_list = Field(event_list, 1);
+       }
+
+       CAMLreturn(events);
+}
+
+value Val_poll(short event)
+{
+       CAMLparam0();
+       CAMLlocal1(res);
+
+       switch (event) {
+               case POLLIN: res = Val_int(0); break;
+               case POLLPRI: res = Val_int(1); break;
+               case POLLOUT: res = Val_int(2); break;
+               case POLLERR: res = Val_int(3); break;
+               case POLLHUP: res = Val_int(4); break;
+               case POLLNVAL: res = Val_int(5); break;
+               default: failwith_xl(ERROR_FAIL, "cannot convert poll event 
value"); break;
+       }
+
+       CAMLreturn(res);
+}
+
+value add_event(value event_list, short event)
+{
+       CAMLparam1(event_list);
+       CAMLlocal1(new_list);
+
+       new_list = caml_alloc(2, 0);
+       Store_field(new_list, 0, Val_poll(event));
+       Store_field(new_list, 1, event_list);
+
+       CAMLreturn(new_list);
+}
+
+value Val_poll_events(short events)
+{
+       CAMLparam0();
+       CAMLlocal1(event_list);
+
+       event_list = Val_emptylist;
+       if (events & POLLIN)
+               event_list = add_event(event_list, POLLIN);
+       if (events & POLLPRI)
+               event_list = add_event(event_list, POLLPRI);
+       if (events & POLLOUT)
+               event_list = add_event(event_list, POLLOUT);
+       if (events & POLLERR)
+               event_list = add_event(event_list, POLLERR);
+       if (events & POLLHUP)
+               event_list = add_event(event_list, POLLHUP);
+       if (events & POLLNVAL)
+               event_list = add_event(event_list, POLLNVAL);
+
+       CAMLreturn(event_list);
+}
+
+int fd_register(void *user, int fd, void **for_app_registration_out,
+                     short events, void *for_libxl)
+{
+       CAMLparam0();
+       CAMLlocalN(args, 4);
+       static value *func = NULL;
+       value *p = (value *) user;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_fd_register");
+       }
+
+       args[0] = *p;
+       args[1] = Val_int(fd);
+       args[2] = Val_poll_events(events);
+       args[3] = (value) for_libxl;
+
+       caml_callbackN(*func, 4, args);
+       CAMLreturn(0);
+}
+
+int fd_modify(void *user, int fd, void **for_app_registration_update,
+                   short events)
+{
+       CAMLparam0();
+       CAMLlocalN(args, 3);
+       static value *func = NULL;
+       value *p = (value *) user;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_fd_modify");
+       }
+
+       args[0] = *p;
+       args[1] = Val_int(fd);
+       args[2] = Val_poll_events(events);
+
+       caml_callbackN(*func, 3, args);
+       CAMLreturn(0);
+}
+
+void fd_deregister(void *user, int fd, void *for_app_registration)
+{
+       CAMLparam0();
+       CAMLlocalN(args, 2);
+       static value *func = NULL;
+       value *p = (value *) user;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_fd_deregister");
+       }
+
+       args[0] = *p;
+       args[1] = Val_int(fd);
+
+       caml_callbackN(*func, 2, args);
+       CAMLreturn0;
+}
+
+int timeout_register(void *user, void **for_app_registration_out,
+                          struct timeval abs, void *for_libxl)
+{
+       CAMLparam0();
+       CAMLlocalN(args, 4);
+       static value *func = NULL;
+       value *p = (value *) user;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_timeout_register");
+       }
+
+       args[0] = *p;
+       args[1] = Val_int(abs.tv_sec);
+       args[2] = Val_int(abs.tv_usec);
+       args[3] = (value) for_libxl;
+
+       caml_callbackN(*func, 4, args);
+       CAMLreturn(0);
+}
+
+int timeout_modify(void *user, void **for_app_registration_update,
+                         struct timeval abs)
+{
+       CAMLparam0();
+       static value *func = NULL;
+       value *p = (value *) user;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_timeout_modify");
+       }
+
+       caml_callback(*func, *p);
+       CAMLreturn(0);
+}
+
+void timeout_deregister(void *user, void *for_app_registration)
+{
+       failwith_xl(ERROR_FAIL, "timeout_deregister not yet implemented");
+       return;
+}
+
+value stub_libxl_osevent_register_hooks(value ctx, value user)
+{
+       CAMLparam2(ctx, user);
+       CAMLlocal1(result);
+       libxl_osevent_hooks *hooks;
+       value *p;
+
+       hooks = malloc(sizeof(*hooks));
+       if (!hooks)
+               failwith_xl(ERROR_NOMEM, "cannot allocate osevent hooks");
+       hooks->fd_register = fd_register;
+       hooks->fd_modify = fd_modify;
+       hooks->fd_deregister = fd_deregister;
+       hooks->timeout_register = timeout_register;
+       hooks->timeout_modify = timeout_modify;
+       hooks->timeout_deregister = timeout_deregister;
+
+       p = malloc(sizeof(value));
+       if (!p)
+               failwith_xl(ERROR_NOMEM, "cannot allocate value");
+       *p = user;
+       caml_register_global_root(p);
+
+       libxl_osevent_register_hooks(CTX, hooks, (void *) p);
+
+       result = caml_alloc(1, Abstract_tag);
+       *((libxl_osevent_hooks **) result) = hooks;
+
+       CAMLreturn(result);
+}
+
+value stub_libxl_osevent_occurred_fd(value ctx, value for_libxl, value fd,
+       value events, value revents)
+{
+       CAMLparam5(ctx, for_libxl, fd, events, revents);
+       libxl_osevent_occurred_fd(CTX, (void *) for_libxl, Int_val(fd),
+               Poll_events_val(events), Poll_events_val(revents));
+       CAMLreturn(Val_unit);
+}
+
+value stub_libxl_osevent_occurred_timeout(value ctx, value for_libxl)
+{
+       CAMLparam2(ctx, for_libxl);
+       libxl_osevent_occurred_timeout(CTX, (void *) for_libxl);
+       CAMLreturn(Val_unit);
+}
+
+struct user_with_ctx {
+       libxl_ctx *ctx;
+       value user;
+};
+
+void event_occurs(void *user, libxl_event *event)
+{
+       CAMLparam0();
+       CAMLlocalN(args, 2);
+       struct user_with_ctx *c_user = (struct user_with_ctx *) user;
+       static value *func = NULL;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_event_occurs_callback");
+       }
+
+       args[0] = c_user->user;
+       args[1] = Val_event(event);
+       libxl_event_free(c_user->ctx, event);
+
+       caml_callbackN(*func, 2, args);
+       CAMLreturn0;
+}
+
+void disaster(void *user, libxl_event_type type,
+                     const char *msg, int errnoval)
+{
+       CAMLparam0();
+       CAMLlocalN(args, 4);
+       struct user_with_ctx *c_user = (struct user_with_ctx *) user;
+       static value *func = NULL;
+
+       if (func == NULL) {
+               /* First time around, lookup by name */
+               func = caml_named_value("libxl_event_disaster_callback");
+       }
+
+       args[0] = c_user->user;
+       args[1] = Val_event_type(type);
+       args[2] = caml_copy_string(msg);
+       args[3] = Val_int(errnoval);
+
+       caml_callbackN(*func, 4, args);
+       CAMLreturn0;
+}
+
+value stub_libxl_event_register_callbacks(value ctx, value user)
+{
+       CAMLparam2(ctx, user);
+       CAMLlocal1(result);
+       struct user_with_ctx *c_user = NULL;
+       libxl_event_hooks *hooks;
+
+       c_user = malloc(sizeof(*c_user));
+       if (!c_user)
+               failwith_xl(ERROR_NOMEM, "cannot allocate user value");
+       c_user->user = user;
+       c_user->ctx = CTX;
+       caml_register_global_root(&c_user->user);
+
+       hooks = malloc(sizeof(*hooks));
+       if (!hooks)
+               failwith_xl(ERROR_NOMEM, "cannot allocate event hooks");
+       hooks->event_occurs_mask = LIBXL_EVENTMASK_ALL;
+       hooks->event_occurs = event_occurs;
+       hooks->disaster = disaster;
+
+       libxl_event_register_callbacks(CTX, hooks, (void *) c_user);
+       result = caml_alloc(1, Abstract_tag);
+       *((libxl_event_hooks **) result) = hooks;
+
+       CAMLreturn(result);
+}
+
+value stub_libxl_evenable_domain_death(value ctx, value domid, value user)
+{
+       CAMLparam3(ctx, domid, user);
+       libxl_evgen_domain_death *evgen_out;
+
+       libxl_evenable_domain_death(CTX, Int_val(domid), Int_val(user), 
&evgen_out);
+
+       CAMLreturn(Val_unit);
+}
+
 /*
  * Local variables:
  *  indent-tabs-mode: t
-- 
1.7.10.4


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