Previously sent via private mail that doesn't seem to go thru - resend 
via office mailer.

Note that other than few exceptions, most of the current filesystem 
and/or drivers do not have aio cancel specifically defined 
(kiob->ki_cancel field is mostly NULL). However, sys_io_cancel system 
call universally sets return code to -EGAIN. This gives applications a 
wrong impression that this call is implemented but just never works. We 
have customer inquires about this issue.

Upload a trivial patch to address this confusion.

-- Wendy