linux-kernel - Re: [RFC][PATCH 0/4] Object creation with a specified id

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Message-ID: <4804F971.3020207@cs.columbia.edu>
Date:	Tue, 15 Apr 2008 14:52:33 -0400
From:	Oren Laadan <orenl@...columbia.edu>
To:	Nadia Derbey <Nadia.Derbey@...l.net>
CC:	Nick Andrew <nick@...k-andrew.net>, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [RFC][PATCH 0/4] Object creation with a specified id



Nadia Derbey wrote:
> Nick Andrew wrote:
>> On Fri, Apr 04, 2008 at 04:51:29PM +0200, Nadia.Derbey@...l.net wrote:
>>
>>>   . echo "LONG XX" > /proc/self/next_id
>>>     next object to be created will have an id set to XX
>>>   . echo "LONG<n> X0 ... X<n-1>" > /proc/self/next_id
>>>     next object to be created will have its ids set to XX0, ... X<n-1>
>>>     This is particularly useful for processes that may have several 
>>> ids if
>>>     they belong to nested namespaces.
>>
>>
>> How do you handle race conditions, i.e. you specify the ID for the
>> next object to be created, and then some other thread goes and creates
>> an object before your thread creates one?
>>
>> Nick.
> 
> 
> Sorry for not answering earlier, I just saw your e-mail!

[I too managed to miss that message].

> 
> It's true that the way I've done things, the "create_with_id" doesn't 
> take into account multi-threaded apps, since "self" is related to the 
> thread group leader.
> 
> May be using something like /proc/self/task/<my_tid>/next_id would be 
> better, but I have to think more about it...

That /proc/self links to /proc/TGID slipped my mind. Definitely must
be done on a per-thread basis (and /proc/<TGID>/task/<PID>/next_id
will do the trick).

Oren.

> 
> Regards,
> Nadia
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