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

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Message-ID: <CACVxJT-Yff7nw2Qd3WX8AbQ2259OgN_fgQ7TvgNMv8A=ysg2JA@mail.gmail.com>
Date:	Thu, 12 Apr 2012 16:35:53 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"H. Peter Anvin" <hpa@...or.com>, 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 Thu, Apr 12, 2012 at 2:11 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> On Thu, 12 Apr 2012 13:54:25 +0300
> Alexey Dobriyan <adobriyan@...il.com> wrote:
>
>> On Sat, Apr 7, 2012 at 12:02 AM, H. Peter Anvin <hpa@...or.com> wrote:
>> > On 04/06/2012 01:16 PM, Alexey Dobriyan wrote:
>> >>
>> >> 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.
>> >>
>> >
>> > I call shenanigans on this.  There is no reason to ENOMEM on the second
>> > written using the fdwalk() implementation I already posted, for example.
>>
>> open("/proc/self/fd") can fail with ENOMEM.
>
> Any syscall can fail with a process kill due to a stack extend on out of
> memory in most configurations. That includes your nextfd stuff
>
> This whole thing is getting stupid. "Perfection is the enemy of
> success".
>
> Your code will also fail when the cat pees on the computer, when the
> power fails and when disk dies. I suspect that other than the cat these
> are all more likely real world cases than your ENOMEM.

You can't see I'm talking about difference only, can you?
Have you read what hpa wrote exactly and what exactly I was answering to?
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