linux-kernel - Re: [v11][PATCH 9/9] Document clone_with

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Message-ID: <20091108150935.GA14991@us.ibm.com>
Date:	Sun, 8 Nov 2009 09:09:35 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Oren Laadan <orenl@...rato.com>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>, arnd@...db.de,
	Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>, hpa@...or.com,
	Pavel Emelyanov <xemul@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>, roland@...hat.com
Subject: Re: [v11][PATCH 9/9] Document clone_with_pids() syscall

Quoting Oren Laadan (orenl@...rato.com):
> Sukadev Bhattiprolu wrote:
> > Matt Helsley [matthltc@...ibm.com] wrote:
> > | > If userspace passes an array with n pids and there are k namespace levels
> > | > then clone_with_pids() makes sure that the kernel sees a pid array like:
> > | > 
> > | > index	  0     ... k - (n + 1)        ...          k - 1
> > | > 	+-----------------------+-------------------------+
> > | > pid_t	| 0 ..................0 | <copied from userspace> |
> > | > 	+-----------------------+-------------------------+
> > | 
> > | (diagram assumes n != k. If n == k then pids[0] is the pid desired
> > | in the initial namespace..)
> > 
> > True.
> > 
> > Also I was not sure if we should prevent choosing pids in ancestor containers.
> > since a process is not even supposed to know of ancestor namespaces. Is there
> > a need for choosing pids in those namespaces.

Yes, that is necessary.

> > | I don't know if it makes more sense to change clone_with_pids() or have
> > | [e]glibc wrappers swap the array contents.
> 
> I prefer to decide now on an order and stick to it in the kernel and
> in glibc.

Agreed!

I'd forgotten that, as Matt said, we can just specify pids to the depth
that we want, so I guess the current order is fine.

-serge
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