From: Davide Libenzi <davidel@xmailserver.org>

The attached patch implements the one-shot support for epoll.  Because of
the way epoll works (hooking f_op->poll()) the ET behavior is not really ET
because it might happen that, while data is still available to read (for
the EPOLLIN case), another chunk will become available triggering another
event.

While those conditions can be easily be handled in userspace, the absolute
triviality of the patch and the avoidance of user/kernel space switches and
f_op->poll() calls, make IMHO worth doing this inside epoll itself.