linux-kernel - Re: Syslets, Threadlets, generic AIO support, v6

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Message-ID: <465DE992.6070803@redhat.com>
Date:	Wed, 30 May 2007 14:16:02 -0700
From:	Ulrich Drepper <drepper@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	Zach Brown <zach.brown@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Syslets, Threadlets, generic AIO support, v6

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Linus Torvalds wrote:
> 	for (i = 0; i < NR_OPEN; i++)
> 		close(i);
> 
> to clean up all file descriptors before doing something new. And yes, I 
> think it was bash that used to *literally* do something like that a long 
> time ago.

Indeed.  It was not only bash, though, I fixed probably a dozen
applications.  But even the new and better solution (readdir of
/proc/self/fd) does not prevent the problem of closing descriptors the
system might still need and the application doesn't know about.

> Which *could* be something as simple as saying "bit 30 in the file 
> descriptor specifies a separate fd space" along with some flags to make 
> open and friends return those separate fd's.

I don't like special cases.  For me things better come in quantities 0,
1, and unlimited (well, reasonable high limit).  Otherwise, who gets to
use that special namespace?  The C library is not the only body of code
which would want to use descriptors.

And then the semantics: do these descriptors should show up in
/proc/self/fd?  Are there separate directories for each namespace?  Do
they count against the rlimit?

This seems to me like a shot from the hips without thinking about other
possibilities.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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