Re: [Qemu-devel] [RFC PATCH v2 02/15] qapi: Eliminate indirection through qmp_event_get_func_emit()

[Marc-André Lureau]

On Tue, Dec 18, 2018 at 10:27 PM Markus Armbruster <address@hidden> wrote:
>
> The qapi_event_send_FOO() functions emit events like this:
>
>     QMPEventFuncEmit emit;
>
>     emit = qmp_event_get_func_emit();
>     if (!emit) {
>         return;
>     }
>
>     qmp = qmp_event_build_dict("FOO");
>     [put event arguments into @qmp...]
>
>     emit(QAPI_EVENT_FOO, qmp);
>
> The value of qmp_event_get_func_emit() depends only on the program:
>
> * In qemu-system-FOO, it's always monitor_qapi_event_queue.
>
> * In tests/test-qmp-event, it's always event_test_emit.
>
> * In all other programs, it's always null.
>
> This is exactly the kind of dependence the linker is supposed to
> resolve; we don't actually need an indirection.
>
> Note that things would fall apart if we linked more than one QAPI
> schema into a single program: each set of qapi_event_send_FOO() uses
> its own event enumeration, yet they share a single emit function.
> Which takes the event enumeration as an argument.  Which one if
> there's more than one?
>
> More seriously: how does this work even now?  qemu-system-FOO wants
> QAPIEvent, and passes a function taking that to
> qmp_event_set_func_emit().  test-qmp-event wants test_QAPIEvent, and
> passes a function taking that to qmp_event_set_func_emit().
>
> I works by type trickery, of course:
>
>     typedef void (*QMPEventFuncEmit)(unsigned event, QDict *dict);
>
>     void qmp_event_set_func_emit(QMPEventFuncEmit emit);
>
>     QMPEventFuncEmit qmp_event_get_func_emit(void);
>
> We use unsigned instead of the enumeration type.  Relies on both
> enumerations boiling down to unsigned, which happens to be true for
> the compilers we use.
>
> Clean this up as follows:
>
> * Generate qapi_event_send_FOO() that call PREFIX_qapi_event_emit()
>   instead of the value of qmp_event_set_func_emit().
>
> * Generate a prototype for PREFIX_qapi_event_emit() into
>   qapi-events.h.
>
> * PREFIX_ is empty for qapi/qapi-schema.json, and test_ for
>   tests/qapi-schema/qapi-schema-test.json.  It's qga_ for
>   qga/qapi-schema.json, and doc-good- for
>   tests/qapi-schema/doc-good-qapi-doc.texi, but those don't define any
>   events.
>
> * Rename monitor_qapi_event_queue() to qapi_event_emit() instead of
>   passing it to qmp_event_set_func_emit().  This takes care of
>   qemu-system-FOO.
>
> * Rename event_test_emit() to test_qapi_event_emit() instead of
>   passing it to qmp_event_set_func_emit().  This takes care of
>   tests/test-qmp-event.
>
> * Add a qapi_event_emit() that does nothing to stubs/monitor.c.  This
>   takes care of all other programs that link code emitting QMP events.
>
> * Drop qmp_event_set_func_emit(), qmp_event_get_func_emit().
>
> Signed-off-by: Markus Armbruster <address@hidden>

Reviewed-by: Marc-André Lureau <address@hidden>

> ---
>  docs/devel/qapi-code-gen.txt |  8 +-------
>  include/qapi/qmp-event.h     |  6 ------
>  monitor.c                    |  4 +---
>  qapi/qmp-event.c             | 12 ------------
>  scripts/qapi/events.py       | 24 ++++++++++++++----------
>  stubs/monitor.c              |  5 +++++
>  tests/Makefile.include       |  4 ++--
>  tests/test-qmp-event.c       |  6 +-----
>  8 files changed, 24 insertions(+), 45 deletions(-)
>
> diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
> index 418a607842..87183d3a09 100644
> --- a/docs/devel/qapi-code-gen.txt
> +++ b/docs/devel/qapi-code-gen.txt
> @@ -1385,16 +1385,10 @@ Example:
>      void qapi_event_send_my_event(void)
>      {
>          QDict *qmp;
> -        QMPEventFuncEmit emit;
> -
> -        emit = qmp_event_get_func_emit();
> -        if (!emit) {
> -            return;
> -        }
>
>          qmp = qmp_event_build_dict("MY_EVENT");
>
> -        emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp);
> +        example_qapi_event_emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp);
>
>          qobject_unref(qmp);
>      }
> diff --git a/include/qapi/qmp-event.h b/include/qapi/qmp-event.h
> index 23e588ccf8..b60f1d3a89 100644
> --- a/include/qapi/qmp-event.h
> +++ b/include/qapi/qmp-event.h
> @@ -14,11 +14,5 @@
>  #ifndef QMP_EVENT_H
>  #define QMP_EVENT_H
>
> -typedef void (*QMPEventFuncEmit)(unsigned event, QDict *dict);
> -
> -void qmp_event_set_func_emit(QMPEventFuncEmit emit);
> -
> -QMPEventFuncEmit qmp_event_get_func_emit(void);
> -
>  QDict *qmp_event_build_dict(const char *event_name);
>  #endif
> diff --git a/monitor.c b/monitor.c
> index 0ad54d8b11..d7ca587bb0 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -590,8 +590,7 @@ monitor_qapi_event_queue_no_reenter(QAPIEvent event, 
> QDict *qdict)
>      qemu_mutex_unlock(&monitor_lock);
>  }
>
> -static void
> -monitor_qapi_event_queue(QAPIEvent event, QDict *qdict)
> +void qapi_event_emit(QAPIEvent event, QDict *qdict)
>  {
>      /*
>       * monitor_qapi_event_queue_no_reenter() is not reentrant: it
> @@ -704,7 +703,6 @@ static void monitor_qapi_event_init(void)
>  {
>      monitor_qapi_event_state = g_hash_table_new(qapi_event_throttle_hash,
>                                                  qapi_event_throttle_equal);
> -    qmp_event_set_func_emit(monitor_qapi_event_queue);
>  }
>
>  static void handle_hmp_command(Monitor *mon, const char *cmdline);
> diff --git a/qapi/qmp-event.c b/qapi/qmp-event.c
> index 5b8854043e..81ddd5331f 100644
> --- a/qapi/qmp-event.c
> +++ b/qapi/qmp-event.c
> @@ -19,18 +19,6 @@
>  #include "qapi/qmp/qdict.h"
>  #include "qapi/qmp/qjson.h"
>
> -static QMPEventFuncEmit qmp_emit;
> -
> -void qmp_event_set_func_emit(QMPEventFuncEmit emit)
> -{
> -    qmp_emit = emit;
> -}
> -
> -QMPEventFuncEmit qmp_event_get_func_emit(void)
> -{
> -    return qmp_emit;
> -}
> -
>  static void timestamp_put(QDict *qdict)
>  {
>      int err;
> diff --git a/scripts/qapi/events.py b/scripts/qapi/events.py
> index 37ee5de682..d86a2d2b3e 100644
> --- a/scripts/qapi/events.py
> +++ b/scripts/qapi/events.py
> @@ -58,7 +58,7 @@ def gen_param_var(typ):
>      return ret
>
>
> -def gen_event_send(name, arg_type, boxed, event_enum_name):
> +def gen_event_send(name, arg_type, boxed, event_enum_name, event_emit):
>      # FIXME: Our declaration of local variables (and of 'errp' in the
>      # parameter list) can collide with exploded members of the event's
>      # data type passed in as parameters.  If this collision ever hits in
> @@ -70,7 +70,6 @@ def gen_event_send(name, arg_type, boxed, event_enum_name):
>  %(proto)s
>  {
>      QDict *qmp;
> -    QMPEventFuncEmit emit;
>  ''',
>                  proto=build_event_send_proto(name, arg_type, boxed))
>
> @@ -86,11 +85,6 @@ def gen_event_send(name, arg_type, boxed, event_enum_name):
>
>      ret += mcgen('''
>
> -    emit = qmp_event_get_func_emit();
> -    if (!emit) {
> -        return;
> -    }
> -
>      qmp = qmp_event_build_dict("%(name)s");
>
>  ''',
> @@ -121,9 +115,10 @@ def gen_event_send(name, arg_type, boxed, 
> event_enum_name):
>  ''')
>
>      ret += mcgen('''
> -    emit(%(c_enum)s, qmp);
> +    %(event_emit)s(%(c_enum)s, qmp);
>
>  ''',
> +                 event_emit=event_emit,
>                   c_enum=c_enum_const(event_enum_name, name))
>
>      if arg_type and not arg_type.is_empty():
> @@ -145,6 +140,7 @@ class 
> QAPISchemaGenEventVisitor(QAPISchemaModularCVisitor):
>              ' * Schema-defined QAPI/QMP events', __doc__)
>          self._event_enum_name = c_name(prefix + 'QAPIEvent', protect=False)
>          self._event_enum_members = []
> +        self._event_emit_name = c_name(prefix + 'qapi_event_emit')
>
>      def _begin_module(self, name):
>          types = self._module_basename('qapi-types', name)
> @@ -170,15 +166,23 @@ class 
> QAPISchemaGenEventVisitor(QAPISchemaModularCVisitor):
>
>      def visit_end(self):
>          (genc, genh) = self._module[self._main_module]
> -        genh.add(gen_enum(self._event_enum_name, self._event_enum_members))
> +        genh.add(gen_enum(self._event_enum_name,
> +                          self._event_enum_members))
>          genc.add(gen_enum_lookup(self._event_enum_name,
>                                   self._event_enum_members))
> +        genh.add(mcgen('''
> +
> +void %(event_emit)s(%(event_enum)s event, QDict *qdict);
> +''',
> +                       event_emit=self._event_emit_name,
> +                       event_enum=self._event_enum_name))
>
>      def visit_event(self, name, info, ifcond, arg_type, boxed):
>          with ifcontext(ifcond, self._genh, self._genc):
>              self._genh.add(gen_event_send_decl(name, arg_type, boxed))
>              self._genc.add(gen_event_send(name, arg_type, boxed,
> -                                          self._event_enum_name))
> +                                          self._event_enum_name,
> +                                          self._event_emit_name))
>          self._event_enum_members.append(QAPISchemaMember(name, ifcond))
>
>
> diff --git a/stubs/monitor.c b/stubs/monitor.c
> index 3890771bb5..32bd7012c3 100644
> --- a/stubs/monitor.c
> +++ b/stubs/monitor.c
> @@ -1,5 +1,6 @@
>  #include "qemu/osdep.h"
>  #include "qapi/error.h"
> +#include "qapi/qapi-events.h"
>  #include "qemu-common.h"
>  #include "monitor/monitor.h"
>
> @@ -14,3 +15,7 @@ int monitor_get_fd(Monitor *mon, const char *name, Error 
> **errp)
>  void monitor_init(Chardev *chr, int flags)
>  {
>  }
> +
> +void qapi_event_emit(QAPIEvent event, QDict *qdict)
> +{
> +}
> diff --git a/tests/Makefile.include b/tests/Makefile.include
> index 3f5a1d0c30..53edd6b57c 100644
> --- a/tests/Makefile.include
> +++ b/tests/Makefile.include
> @@ -519,7 +519,7 @@ QEMU_CFLAGS += -I$(SRC_PATH)/tests
>  test-util-obj-y = libqemuutil.a
>  test-qom-obj-y = $(qom-obj-y) $(test-util-obj-y)
>  test-qapi-obj-y = tests/test-qapi-visit.o tests/test-qapi-types.o \
> -       tests/test-qapi-events.o tests/test-qapi-introspect.o \
> +       tests/test-qapi-introspect.o \
>         $(test-qom-obj-y)
>  benchmark-crypto-obj-y = $(crypto-obj-y) $(test-qom-obj-y)
>  test-crypto-obj-y = $(crypto-obj-y) $(test-qom-obj-y)
> @@ -611,7 +611,7 @@ tests/qapi-schema/doc-good.test.texi: 
> $(SRC_PATH)/tests/qapi-schema/doc-good.jso
>
>  tests/test-string-output-visitor$(EXESUF): 
> tests/test-string-output-visitor.o $(test-qapi-obj-y)
>  tests/test-string-input-visitor$(EXESUF): tests/test-string-input-visitor.o 
> $(test-qapi-obj-y)
> -tests/test-qmp-event$(EXESUF): tests/test-qmp-event.o $(test-qapi-obj-y)
> +tests/test-qmp-event$(EXESUF): tests/test-qmp-event.o $(test-qapi-obj-y) 
> tests/test-qapi-events.o
>  tests/test-qobject-output-visitor$(EXESUF): 
> tests/test-qobject-output-visitor.o $(test-qapi-obj-y)
>  tests/test-clone-visitor$(EXESUF): tests/test-clone-visitor.o 
> $(test-qapi-obj-y)
>  tests/test-qobject-input-visitor$(EXESUF): 
> tests/test-qobject-input-visitor.o $(test-qapi-obj-y)
> diff --git a/tests/test-qmp-event.c b/tests/test-qmp-event.c
> index 9cddd72adb..bf900f14f4 100644
> --- a/tests/test-qmp-event.c
> +++ b/tests/test-qmp-event.c
> @@ -93,9 +93,7 @@ static bool qdict_cmp_simple(QDict *a, QDict *b)
>      return d.result;
>  }
>
> -/* This function is hooked as final emit function, which can verify the
> -   correctness. */
> -static void event_test_emit(test_QAPIEvent event, QDict *d)
> +void test_qapi_event_emit(test_QAPIEvent event, QDict *d)
>  {
>      QDict *t;
>      int64_t s, ms;
> @@ -241,8 +239,6 @@ static void test_event_d(TestEventData *data,
>
>  int main(int argc, char **argv)
>  {
> -    qmp_event_set_func_emit(event_test_emit);
> -
>      g_test_init(&argc, &argv, NULL);
>
>      event_test_add("/event/event_a", test_event_a);
> --
> 2.17.2
>
>


-- 
Marc-André Lureau