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

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Date:	Fri, 26 Feb 2010 17:52:03 -0500
From:	Oren Laadan <orenl@...columbia.edu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Pavel Emelyanov <xemul@...allels.com>,
	Ben Greear <greearb@...delatech.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.



Eric W. Biederman wrote:
> Oren Laadan <orenl@...columbia.edu> 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?
>> That's how I understood the question, and I, too, wonder why not ?
>>
>> By the way, an alternative to using bitmap is to change the prototype
>> of setns() to accept an array of FD's:
>>
>> 	int setns(int *fds, int nfds);
>>
>> So the process will atomically enter all the namespaces as specified
>> by the FDs.
> 
> We could.  Mostly I implemented things in the simplest way possible.
> 
> Semantically I know of no reason why need to enter more than one namespace
> at once, and I don't expect entering a namespace to be on anyone's fast
> path so every last drop of performance was not crucial.
> 
> The only justification I can think of for more than one namespace at a
> time is that because we have a synchronize_rcu() in the kernel we can
> loop in the kernel much more quickly than we can loop in userspace.

Can't think of a specific scenario, but I wonder if there would
be a problem (security or otherwise) with a process that only
partly belongs to a container, even if for a short time ?

Oren.
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