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

[Eric Blake]

On 12/18/18 12:22 PM, Markus Armbruster wrote:
> The qapi_event_send_FOO() functions emit events like this:
>
>      QMPEventFuncEmit emit;
>
>      emit = qmp_event_get_func_emit();
>      if (!emit) {
>          return;
>      }

>      emit(QAPI_EVENT_FOO, qmp);

> 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:

s/I/It/

>      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.

Wait - PREFIX is qga_ or doc_good_...

> * 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.

...but the stub function is defined without a prefix?

> +++ 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)
> +{
> +}
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org