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

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Message-ID: <180e9441-edd7-4a47-a307-eb3a8da45457@email.android.com>
Date:	Fri, 06 Apr 2012 13:33:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alexey Dobriyan <adobriyan@...il.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)

What is unreliable about it?  This is starting to be ridiculous.  As far as automounting /proc is concerned, this does not seem to be a significant problem with current userspace.

Alexey Dobriyan <adobriyan@...il.com> wrote:

>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.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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