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

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Message-ID: <CAHGf_=qkdUBYVTGzqpmmviCsn93gPFEKeS8eZR2fNN-d0NdYpQ@mail.gmail.com>
Date:	Tue, 10 Apr 2012 20:12:17 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Ben Pfaff <blp@...stanford.edu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Alexey Dobriyan <adobriyan@...il.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 Sat, Apr 7, 2012 at 5:21 PM, Ben Pfaff <blp@...stanford.edu> wrote:
> "H. Peter Anvin" <hpa@...or.com> writes:
>
>> On 04/06/2012 02:54 AM, Alexey Dobriyan wrote:
>>>
>>> Without proc knowledge about fdtable is gathered linearly and still unreliable.
>>> With nextfd(2), even procful environments could lose several failure branches.
>>> And they can keep old dumb fd++ or smart /proc/self/fd loops for a change.
>>>
>>
>> Incidentally, if we were to create a system call for this -- which I so
>> far see no reason for -- I would make it return a select-style bitmask
>> of file descriptors in use, not a "next fd" which would require a system
>> call per iteration.
>
> It's already possible to do something a little like that with the
> existing "poll" system call:
>
> #include <stdio.h>
> #include <sys/poll.h>
>
> int
> main(void)
> {
>  enum { N_FDS = 1024 };
>  struct pollfd fds[N_FDS];

Your code has a muximum fd assumption here. that is one of that we
really want to avoid.
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