main loop: macros to mark GS and I/O functions

Righ now, IO_CODE and IO_OR_GS_CODE are nop, as there isn't
really a way to check that a function is only called in I/O.
On the other side, we can use qemu_in_main_thread() to check if
we are in the main loop.

The usage of macros makes easy to extend them in the future without
making changes in all callers. They will also visually help understanding
in which category each function is, without looking at the header.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20220303151616.325444-3-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

include/qemu/main-loop.h

@@ -269,6 +269,24 @@ bool qemu_mutex_iothread_locked(void);
  */
 bool qemu_in_main_thread(void);
 
+/* Mark and check that the function is part of the global state API. */
+#define GLOBAL_STATE_CODE()                                         \
+    do {                                                            \
+        assert(qemu_in_main_thread());                              \
+    } while (0)
+
+/* Mark and check that the function is part of the I/O API. */
+#define IO_CODE()                                                   \
+    do {                                                            \
+        /* nop */                                                   \
+    } while (0)
+
+/* Mark and check that the function is part of the "I/O OR GS" API. */
+#define IO_OR_GS_CODE()                                             \
+    do {                                                            \
+        /* nop */                                                   \
+    } while (0)
+
 /**
  * qemu_mutex_lock_iothread: Lock the main loop mutex.
  *