netdev - Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

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Date:	Sat, 27 Feb 2010 11:08:35 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	hadi@...erus.ca, Daniel Lezcano <dlezcano@...ibm.com>,
	Patrick McHardy <kaber@...sh.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	Ben Greear <greearb@...delatech.com>,
	Serge Hallyn <serue@...ibm.com>,
	Matt Helsley <matthltc@...ibm.com>
Subject: Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

Pavel Emelyanov <xemul@...allels.com> writes:

> Eric W. Biederman wrote:
>> Pavel Emelyanov <xemul@...allels.com> writes:
>> 
>>> Thanks. What's the problem with setns?
>> 
>> joining a preexisting namespace is roughly the same problem as
>> unsharing a namespace.  We simply haven't figure out how to do it
>> safely for the pid and the uid namespaces.
>
> The pid may change after this for sure. What problems do you know
> about it? What if we try to allocate the same PID in a new space
> or return -EBUSY? This will be a good starting point. If we manage
> to fix it later this will not break the API at all.

Parentage.  The pid is the identity of a process and all kinds of things
make assumptions in all kinds of strange places.  I don't see how
waitpid can work if you change the pid.

glibc doesn't cope if you change someones pid.

>> Definitely.  I only consider the current interface to be a mushy not
>> set in stone.
>
> OK. The interface is good. I just don't want you to send it for an inclusion
> until we decide what to do with waiting.

Sure.  I am get a jump on 2.6.35 not aiming for inclusion this merge
window.  There is plenty of time.

>
> Poll is OK with me. As far as the notification is concerned - that's also
> done in OpenVZ. If you are OK to wait for a week or two I can do it for net
> namespaces.

Seems reasonable.

Eric
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