linux-kernel - Re: [patch 7/8] fdmap v2

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Date:	Wed, 6 Jun 2007 16:29:13 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Eric Dumazet <dada1@...mosbay.com>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

On Thu, 7 Jun 2007, Alan Cox wrote:

> > > 	prctl(PR_SPARSEFD, 1);
> > > 
> > > to turn on sparse fd allocation for a process ?
> > 
> > There was a little discussion where I tried to whisper something similar, 
> > but Linus and Uli shot me :) - with good reasons IMO.
> > You may link to runtimes that are not non-sequentialfd aware, and will 
> > break them.
> 
> Linking to the correct version of a libary and getting the library
> versioning right is not rocket science and isn't a sane excuse. Its no
> different to the stdio to large fd migration issues with many Unixen and
> they all coped just fine.

I don't think it's a matter of versioning. Many userspace libraries 
expects their fds to be compact (for many reasons - they use select, they 
use them to index 0-based arrays, etc...), and if the kernel suddendly 
starts returning values in the 1<<28 up arena, they sure won't be happy.
So I believe that the correct way is that the caller specifically selects 
the feature, leaving the legacy fd allocation as default.



- Davide


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