Added a section to the select() hook documentation discussing the FSs

responsibility never to call notify_select_event() after deselect().


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25262 a95241bf-73f2-0310-859d-f6bbb57e9c96

docs/user/drivers/fs_interface.dox

@@ -510,6 +510,15 @@
 	This function is optional. If you don't export it, the default implementation
 	in the VFS will call notify_select_event() directly which will be sufficient
 	for most file systems.
+
+	Note that while select() and the corresponding deselect() are invoked by the
+	same thread, notifications are usually generated by other threads. It is
+	your responsibility to make sure that notify_select_event() is never called
+	for a selectsync object for which deselect() has already returned. This is
+	commonly done by holding the same lock when invoking notify_select_event()
+	and when removing the selectsync object from the cookie in deselect().
+	Such a lock can be any lock, usually one that is associated with the node or
+	the volume.
 */
 
 /*!