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

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Message-ID: <m1mxyvrqvk.fsf@fess.ebiederm.org>
Date:	Sat, 27 Feb 2010 01:04:47 -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:
>> 
>>>>> Yet another set of per-namespace IDs along with CLONE_NEWXXX ones?
>>>>> I currently have a way to create all namespaces we have with one
>>>>> syscall. Why don't we have an ability to enter them all with one syscall?
>>>> The CLONE_NEWXXX series of bits has been an royal pain to work with,
>>>> and it appears to be unnecessary complications for no gain.
>>> That's the answer for the "Yet another set..." question.
>>> How about the "Why don't we have..." one?
>> 
>> I am not certain which question you are asking:
>> 
>> Why don't we have an ability to enter all namespaces with one syscall
>> invocation?
>
> Exactly. Please add at least the NSTYPE_NSPROXY or whatever, that will
> pin all namespaces of a given pid from the very beginning.

For nsfd(2) that is doable.  At least for now setns can't restore it.

>> Why don't we have a syscall that allows us to enter every namespace?
>
> This one is done in the patch, no?
>
> Although the approach is OK for me, there's one design issue, that came
> up to my mind recently: can we use this fd to wail for a namespace to 
> stop? I currently don't see this ability, but this is something I require
> badly.

I have designed these file descriptors to pin the namespaces, so
waiting for them to exit isn't something they can do now.  It makes a
lot of sense to have similar ones that take  weak references to the namespaces
that we can use to wait for a namespace to exit.

Eric
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