chardev/char-fe: Document FEWatchFunc typedef

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230705133139.54419-4-philmd@linaro.org>

include/chardev/char-fe.h

@@ -175,6 +175,20 @@ void qemu_chr_fe_printf(CharBackend *be, const char *fmt, ...)
     G_GNUC_PRINTF(2, 3);
 
 
+/**
+ * FEWatchFunc: a #GSourceFunc called when any conditions requested by
+ *              qemu_chr_fe_add_watch() is satisfied.
+ * @do_not_use: depending on the underlying chardev, a GIOChannel or a
+ *              QIOChannel. DO NOT USE!
+ * @cond: bitwise combination of conditions watched and satisfied
+ *              before calling this callback.
+ * @data: user data passed at creation to qemu_chr_fe_add_watch(). Can
+ *              be NULL.
+ *
+ * Returns: G_SOURCE_REMOVE if the GSource should be removed from the
+ *              main loop, or G_SOURCE_CONTINUE to leave the GSource in
+ *              the main loop.
+ */
 typedef gboolean (*FEWatchFunc)(void *do_not_use, GIOCondition condition, void *data);
 
 /**