linux-kernel - Re: epoll design problems with common fork/exec patterns

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Date:	Sun, 02 Mar 2008 10:11:57 -0500
From:	Sam Varshavchik <mrsam@...rier-mta.com>
To:	linux-man@...r.kernel.org
Cc:	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Chris ¥¯ Heath <chris@...thens.co.nz>,
	David Schwartz <davids@...master.com>, dada1@...mosbay.com,
	Linux-Kernel@...r. Kernel. Org 
	<linux-kernel@...r.kernel.org>
Subject: Re: epoll design problems with common fork/exec patterns

Hijacking this epoll thread, the following related question occurs to me:

#Q8
#    Does an operation on a file descriptor affect the already collected but 
#not yet reported events?
#
#A8
#    You can do two operations on an existing file descriptor. Remove would 
#be meaningless for this case. Modify will re-read available I/O.

Why is EPOLL_CTL_DEL considered meaningless? A process is wrapping up its 
business and is preparing to remove the fd from the epoll set, and then 
close the file descriptor itself. In the meantime, the fd became readable, 
and a POLLIN event gets collected. So, what happens to the collected event, 
when the EPOLL_CTL_DEL operation is made?

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