linux-kernel - Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem

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Message-ID: <20070405141321.GH28414@in.ibm.com>
Date:	Thu, 5 Apr 2007 19:43:21 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	"Paul Menage" <menage@...gle.com>
Cc:	sekharan@...ibm.com, ckrm-tech@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, xemul@...ru, rohitseth@...gle.com,
	pj@....com, "Eric W. Biederman" <ebiederm@...ssion.com>,
	winget@...gle.com, containers@...ts.osdl.org
Subject: Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem

On Thu, Apr 05, 2007 at 06:13:25PM +0530, Srivatsa Vaddagiri wrote:
> Lets go back to the f_bc example here for a moment. Lets say T1 was in C1 and 
> opened file f1. f1->f_bc points to C1->beancounter.
> 
> T1 moves from C1 -> C2, but f1 is not migrated. 
> C1->beancounter.count stays at 1 (to account for f1->f_bc).

Actually C1->beancounter.count should be at 2 (C1->beancounter and
f1->f_bc are pointing to it).

> File f1 is closed. C1->beancounter.count becomes zero.

C1->beancounter.count should go to 1 ..

> Now user issues rmdir C1. If rmdir finds (after taking manage_mutex that
> is)
> 
> 	- zero tasks in C1
> 	- zero refcount in C1->beancounter

s/zero refcount in C1->beancounter/exactly 1 refcount in C1->beancounter

> why is it not safe to assume that C1->beancounter.count will continue to
> stay zero?

s/zero/at one

> Basically I am struggling to answer "How can a zero refcount (beancounter) 
> object go non-zero when zero tasks are attached to it" ..

s/zero/one and s/non-zero/>1

Essentially bc_subsys->can_attach(struct bean_counter *b) can return
-EBUSY if (atomic_read(&b->count) > 1) ..

-- 
Regards,
vatsa
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