linux-kernel - Re: epoll and shared fd's

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Message-ID: <Pine.LNX.4.64.0802261125180.27243@alien.or.mcafeemobile.com>
Date:	Tue, 26 Feb 2008 11:31:21 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
cc:	Pierre Habouzit <madcoder@...ian.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Marc Lehmann <schmorp@...morp.de>,
	David Schwartz <davids@...master.com>
Subject: Re: epoll and shared fd's

On Tue, 26 Feb 2008, Michael Kerrisk wrote:

> Okay -- I'll look at it some more.  I am however loathe to drop the
> term open file description, because POSIX uses, as well as a number of
> other Linux man pages by now.

Heh, POSIX. Now doesn't take a genius to see that "file description" and 
"file descriptor" looks amazingly similar, does it? :)


> > That'd mean placing an eventpoll custom hook into sys_close(). Looks 
> > very bad to me, and probably will look even worse to other kernel 
> > folks. Is not much a performance issue (a check to see if a file* is 
> > an eventpoll file is as easy as comparing the f_op pointer), but a 
> > design/style issue.
>
> Oh -- I wasn't suggesting we could make the change now -- it would
> break the ABI and all that.  I was just wondering why the decision
> wasn't made to do it the other way to begin with.  The existing
> semantics are somewhat couterintuitive, and potentially interact
> libraries that do private manipulations with file descriptors.

For the same reason that a custom hook in sys_close wouldn't have passed 
the radar ;)
As far as problems with libraries doing tricks with fds, that's an issue 
that goes beyond epoll.



- Davide


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