From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
drepper@gmail.com, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] nextfd(2)
Date: Tue, 17 Apr 2012 14:12:09 -0400 [thread overview]
Message-ID: <4F8DB279.4020408@gmail.com> (raw)
In-Reply-To: <4F85EA5E.6070106@zytor.com>
(4/11/12 4:32 PM), H. Peter Anvin wrote:
> On 04/11/2012 01:23 PM, KOSAKI Motohiro wrote:
>>
>> Hmmm.... I'm sorry I don't find "considered undesirable". Maybe because
>> my English is not very good. can you please help me clarify?
>>
>
> I also went and read the mailing list discussion on the topic.
>
> Ulrich, for example (in his usual mild-mannered style), commented:
>
>> And all these programs and systems are wrong.
>>
>> There is no guarantee that one of the fds isn't used behind the
>> scenes for something important which is still running as part of the
>> fork/exec code. It's completely unacceptable to build into the
>> interfaces the assumption that the programmer knows all the file
>> descriptors.
>>
>> This is why using CLOEXEC is the only correct way to deal with this
>> and now there is no exceuse anymore whatsoever. Every fd-creating
>> interface can use CLOEXEC.
>
>> This text says,
>>
>>> so a future revision of the standard may indeed add fdwalk( ), although no
>>> one in the meeting was willing to draft a proposal for fdwalk( ) at this time
>>
>> and, later says after noting F_NEXT and O_CLOEXEC,
>>
>>> Therefore, the rest of this proposal seeks to document the problem
>>> with closing arbitrary file descriptors, and a new bugid will be
>>> opened to propose standardizing some recent interfaces and interface
>>> extensions first appearing in Linux
>>
>> Do you think latter override former?
>
> Yes.
>
>>>>> b) unsafe because there might be file descriptors used by libc itself.
>>>>
>>>> I agree this. Even though almost developer don't use libc message catalogue and
>>>> we can avoid such issue by using nextfd() + fcntl(O_CLOEXEC).
>>>
>>> No, that's exactly the point that we cannot.
>>
>> I thknk we are talking different aspect. I'm talking practical issue.
>> say, ruby hit the exact same issue
>> because valgrind uses internal fds and they don't think their exec()
>> case don't need fd
>> inheritance. Even though it close libc internal fds, invoked new
>> executable may open them
>> again at process strtup code. Therefore, they are using O_CLOEXEC. In
>> the other hands,
>> you seems talking about it is corner case. If so, I agree. I was not
>> argue it. I only say, I
>> haven't seen real world application require it.
>>
>> Personally, I'm only interesting real world issue.
>
> These are real-world issues.
>
>>> The problem -- as was brought up in the POSIX discussion -- is that you
>>> actually end up breaking *properly functioning programs*.
>>
>> But the url only talk about a possibility of misuse.
>
> There are concrete examples on the mailing list.
>
> Anyway, fdwalk() at least exists as an interface. There is absolutely
> no momentum for FD_NEXT that I can see.
Thanks Peter, I guess I now understand what you said. Again, thanks for the
patience. _Personally_ I can't agree Ulrich's opinion because I've only seen
fork-closeall-exec pattern. but, I also can't say there is no other use case.
And, as I already wrote, I don't think fdwalk() is bad taste. I only want to
explain the background of nextfd interface bacause you said you have no seen
the reason and I think I can explain the background and motivation because this
is famous issue in user land folks. (oops, this should be noted, I'm not original
patch author and I talked only about my ovserved issue. Alexey might know another
use cause, I dunnno)
Unfortnately, I'll be offlined full of this and next week and then I have to leave
this thread. But I believe I'm not needed this thread any more. :)
next prev parent reply other threads:[~2012-04-17 18:12 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-01 12:57 [PATCH] nextfd(2) Alexey Dobriyan
2012-04-01 13:58 ` Konstantin Khlebnikov
2012-04-01 21:30 ` Alexey Dobriyan
2012-04-02 0:09 ` Alan Cox
2012-04-02 8:38 ` Konstantin Khlebnikov
2012-04-02 9:26 ` Cyrill Gorcunov
2012-04-01 15:43 ` Eric Dumazet
2012-04-01 21:31 ` Alexey Dobriyan
2012-04-01 21:36 ` Alan Cox
2012-04-01 17:20 ` Linus Torvalds
2012-04-01 18:28 ` Valentin Nechayev
2012-04-01 21:33 ` Alexey Dobriyan
2012-04-01 19:21 ` Arnd Bergmann
2012-04-01 21:35 ` Alexey Dobriyan
2012-04-01 22:05 ` H. Peter Anvin
2012-04-04 12:13 ` Arnd Bergmann
2012-04-01 22:03 ` H. Peter Anvin
2012-04-01 22:13 ` H. Peter Anvin
2012-04-02 0:08 ` Alan Cox
2012-04-30 9:58 ` Valentin Nechayev
2012-04-02 1:19 ` Kyle Moffett
2012-04-02 1:37 ` H. Peter Anvin
2012-04-02 11:37 ` Ulrich Drepper
2012-04-06 9:54 ` Alexey Dobriyan
2012-04-06 15:27 ` Colin Walters
2012-04-06 16:14 ` H. Peter Anvin
2012-04-06 20:16 ` Alexey Dobriyan
2012-04-06 20:33 ` H. Peter Anvin
2012-04-06 21:02 ` H. Peter Anvin
2012-04-12 10:54 ` Alexey Dobriyan
2012-04-12 11:11 ` Alan Cox
2012-04-12 13:35 ` Alexey Dobriyan
2012-04-12 13:51 ` H. Peter Anvin
2012-04-12 19:21 ` Alexey Dobriyan
2012-04-12 14:09 ` Eric Dumazet
2012-04-06 16:23 ` H. Peter Anvin
2012-04-07 21:21 ` Ben Pfaff
2012-04-11 0:12 ` KOSAKI Motohiro
2012-04-11 0:09 ` KOSAKI Motohiro
2012-04-11 17:58 ` H. Peter Anvin
2012-04-11 18:04 ` Linus Torvalds
2012-04-11 18:11 ` H. Peter Anvin
2012-04-11 19:46 ` KOSAKI Motohiro
2012-04-11 19:49 ` H. Peter Anvin
2012-04-11 20:23 ` KOSAKI Motohiro
2012-04-11 20:32 ` H. Peter Anvin
2012-04-17 18:12 ` KOSAKI Motohiro [this message]
2012-04-11 18:00 ` H. Peter Anvin
2012-04-11 19:20 ` KOSAKI Motohiro
2012-04-11 19:22 ` H. Peter Anvin
2012-04-11 19:26 ` KOSAKI Motohiro
2012-04-11 19:28 ` H. Peter Anvin
2012-04-11 19:31 ` KOSAKI Motohiro
2012-04-11 19:32 ` H. Peter Anvin
2012-04-02 23:17 ` KOSAKI Motohiro
2012-04-02 23:56 ` H. Peter Anvin
2012-04-04 11:51 ` Ulrich Drepper
2012-04-04 16:38 ` KOSAKI Motohiro
2012-04-04 16:43 ` Ulrich Drepper
2012-04-04 17:07 ` KOSAKI Motohiro
2012-04-04 17:49 ` Ulrich Drepper
2012-04-04 18:08 ` KOSAKI Motohiro
2012-04-04 16:31 ` KOSAKI Motohiro
2012-04-04 17:10 ` Colin Walters
2012-04-04 17:25 ` Colin Walters
2012-04-04 23:35 ` KOSAKI Motohiro
2012-04-04 18:44 ` H. Peter Anvin
2012-04-03 19:21 ` Colin Walters
2012-04-04 3:01 ` Al Viro
2012-04-04 17:10 ` KOSAKI Motohiro
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