linux-kernel - Re: [patch 1/4] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry v8

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Date:	Tue, 24 Jan 2012 18:11:21 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [patch 1/4] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry v8

KOSAKI Motohiro <kosaki.motohiro@...il.com> writes:

> (1/24/12 4:11 AM), Cyrill Gorcunov wrote:
>> On Tue, Jan 24, 2012 at 12:52:03AM -0800, Eric W. Biederman wrote:
>>> Cyrill Gorcunov<gorcunov@...il.com>  writes:
>>>
>>>> On Tue, Jan 24, 2012 at 04:07:09PM +0900, KAMEZAWA Hiroyuki wrote:
>>>>>>
>>>>>> Hmm. But userspace app will get eof, so frankly I don't see
>>>>>> a problem here. Or maybe I miss something?
>>>>>>
>>>>>
>>>>> Userspace need to take care of whether there may be"\n" or not even
>>>>> if read() returns EOF.
>>>>> As an interface, it's BUG to say "\n" will be there if you're lucky!"
>>>>> (*) I know script language can handle this but we shouldn't assume that.
>>>>>
>>>>> How about just remove "\n" at EOF  ? I think it's unnecessary.
>>>>>
>>>>
>>>> Sure thing, it's not a problem to remove it completely.
>>>
>>> Foolish question.  Is there any reason why this is a file instead
>>> of being the obvious directory full of symlinks?
>>>
>>
>> How would these symlinks look like? "../../pid"? There were a conversation
>> about such things (https://lkml.org/lkml/2011/12/2/142) but I suppose we
>> were agree on children with pids as consensus.
>
> I couldn't find any agreement in this link. Suppose wrong url?

Now that you have reminded me of this thread.  I can say that the
link would need to look like ../../pid.  Our children will always
be thread group leaders, so we can safely point to the /proc/<pid>
directories.  So readlink would return ../../<pid> or however many
dots are needed.  Follow link could just warp us to that directory
as it does for the other magic proc symlinks.

My feeling is that a children subdirectory would be a lot more useful
than a simple file that lists the children.

Eric
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