monitor: mark mixed functions that can suspend

There should be no paths from a coroutine_fn to aio_poll, however in
practice coroutine_mixed_fn will call aio_poll in the !qemu_in_coroutine()
path.  By marking mixed functions, we can track accurately the call paths
that execute entirely in coroutine context, and find more missing
coroutine_fn markers.  This results in more accurate checks that
coroutine code does not end up blocking.

If the marking were extended transitively to all functions that call
these ones, static analysis could be done much more efficiently.
However, this is a start and makes it possible to use vrc's path-based
searches to find potential bugs where coroutine_fns call blocking functions.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qapi/qmp/dispatch.h

@@ -55,8 +55,8 @@ bool qmp_command_available(const QmpCommand *cmd, Error **errp);
 const char *qmp_command_name(const QmpCommand *cmd);
 bool qmp_has_success_response(const QmpCommand *cmd);
 QDict *qmp_error_response(Error *err);
-QDict *qmp_dispatch(const QmpCommandList *cmds, QObject *request,
-                    bool allow_oob, Monitor *cur_mon);
+QDict *coroutine_mixed_fn qmp_dispatch(const QmpCommandList *cmds, QObject *request,
+                                       bool allow_oob, Monitor *cur_mon);
 bool qmp_is_oob(const QDict *dict);
 
 typedef void (*qmp_cmd_callback_fn)(const QmpCommand *cmd, void *opaque);

qapi/qmp-dispatch.c

@@ -134,8 +134,8 @@ static void do_qmp_dispatch_bh(void *opaque)
  * Runs outside of coroutine context for OOB commands, but in coroutine
  * context for everything else.
  */
-QDict *qmp_dispatch(const QmpCommandList *cmds, QObject *request,
-                    bool allow_oob, Monitor *cur_mon)
+QDict *coroutine_mixed_fn qmp_dispatch(const QmpCommandList *cmds, QObject *request,
+                                       bool allow_oob, Monitor *cur_mon)
 {
     Error *err = NULL;
     bool oob;