linux-kernel - Re: [PATCH] nextfd(2)

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Message-ID: <20120406201601.GA3310@p183.telecom.by>
Date:	Fri, 6 Apr 2012 23:16:02 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	torvalds@...ux-foundation.org, drepper@...il.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] nextfd(2)

On Fri, Apr 06, 2012 at 09:14:17AM -0700, H. Peter Anvin wrote:
> On 04/06/2012 02:54 AM, Alexey Dobriyan wrote:
> > 
> > I agree, this particular changelog may be somewhat out of line.
> > 
> > But I find it little hypocritical that kernel developers add CONFIG_PROC_FS,
> > fix compilation problems associated with it, do not mount proc by default,
> > do not mark it unmountable somehow and
> > then say procless setups aren't worth it.
> > 
> 
> Aren't worth *optimizing for*.  But yes, CONFIG_PROC_FS is pretty much a
> historic relic at this point, and probably should just be dropped.

What to do with automounting /proc so it availablility would match
syscall availability?

> > Without proc knowledge about fdtable is gathered linearly and still unreliable.
> > With nextfd(2), even procful environments could lose several failure branches.
> 
> What?  Please explain how on Earth this would "lose several failure
> branches."

closefrom(3) written via nextfd(2) loop is reliable and doesn't fail.
closefrom(3) written via /proc/self/fd is reliable and can fail (including ENOMEM).
closefrom(3) written via close(fd++) is unreliable.

If programmer adds nextfd(2) loop before any closefrom(3) code
he currently uses, there will be less failures.
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