fanotify: Introduce FAN_NOFD

FAN_NOFD is used in fanotify events that do not provide an open file
descriptor (like the overflow_event).
Signed-off-by: NLino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: NEric Paris <eparis@redhat.com>

include/linux/fanotify.h

@@ -101,6 +101,8 @@ struct fanotify_response {
 /* Legit userspace responses to a _PERM event */
 #define FAN_ALLOW	0x01
 #define FAN_DENY	0x02
+/* No fd set in event */
+#define FAN_NOFD	-1
 
 /* Helper functions to deal with fanotify_event_metadata buffers */
 #define FAN_EVENT_METADATA_LEN (sizeof(struct fanotify_event_metadata))