From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.
Date: Wed, 03 Mar 2010 11:47:12 -0800
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Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@parallels.com>,
	Linux Netdev List <netdev@vger.kernel.org>,
	containers@lists.linux-foundation.org,
	Netfilter Development Mailinglist
	<netfilter-devel@vger.kernel.org>,
	Ben Greear <greearb@candelatech.com>
To: "Serge E. Hallyn" <serue@us.ibm.com>
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In-Reply-To: <20100303153800.GA937@us.ibm.com> (Serge E. Hallyn's message of "Wed\, 3 Mar 2010 09\:38\:00 -0600")
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"Serge E. Hallyn" <serue@us.ibm.com> writes:

> Quoting Eric W. Biederman (ebiederm@xmission.com):
>> Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:
>> 
>> > Eric W. Biederman [ebiederm@xmission.com] wrote:
>> > | 
>> > | I think replacing a struct pid for another struct pid allocated in
>> > | descendant pid_namespace (but has all of the same struct upid values
>> > | as the first struct pid) is a disastrous idea.  It destroys the
>> >
>> > True. Sorry, I did not mean we would need a new 'struct pid' for an
>> > existing process. I think we talked earlier of finding a way of attaching
>> > additional pid numbers to the same struct pid.
>> 
>> I just played with this and if you make the semantics of unshare(CLONE_NEWPID)
>> to be that you become the idle task aka pid 0, and not the init task pid 1 the
>> implementation is trivial.
>
> Heh, and then (browsing through your copy_process() patch hunks) the next
> forked task becomes the child reaper for the new pidns?  <shrug>  why not
> I guess.
>
> Now if that child reaper then gets killed, will the idle task get killed too?

No.

> And if not, then idle task can just re-populating the new pidns with new
> idle tasks...

After zap_pid_namespace interesting...

> If this brought us a step closer to entering an existing pidns that would
> be one thing, but is there actually any advantage to being able to
> unshare a new pidns?  Oh, I guess there is - PAM can then use it at
> login, which might be neat.

I have to say that the semantics of my patch are unworkable for
unshare.  Unless I am mistaken for PAM to use it requires that the
current process fully change and become what it needs to be.
Requiring an extra fork to fully complete the process is a problem.

Scratch one bright idea.

Eric