linux-kernel - Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

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Message-ID: <20111113185902.GB4633@redhat.com>
Date:	Sun, 13 Nov 2011 19:59:02 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Glauber Costa <glommer@...allels.com>,
	Nathan Lynch <ntl@...ox.com>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Serge Hallyn <serue@...ibm.com>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [PATCH 3/3] pids: Make it possible to clone tasks with given
	pids

On 11/11, Pavel Emelyanov wrote:
>
> > Yes, sysctl+clone should be "atomic", but that is all. Does it really
> > hurt? OK, if nothing else, can't you do somthing like
> ...
> Nope, as I said to Tejun, we will most likely not forks children in the depth-first
> order,

But this doesn't matter. I think you misunderstood a bit. You can do
set_last_pid+clone at any time. It doesn't depen on previous clone's.
Unless, of course, the necessary pid_nr was already used, but this is
equally true for CLONE_CHILD_USEPIDS.

> But I don't insist.

You should ;)

> If the CLONE_CHILD_USEPIDS has absolutely no way in the kernel we'll
> have to go the uglier path.

All I think is: we should discuss everything we can before we add the
new API. Probably we need a wider CC.

Yes, personally I can't say I like CLONE_CHILD_USEPIDS very much. But
I agree that sysctl(set_last_pid) (or whatever) is not perfect too.
To me, it has only one but very important (imho) advantage: it is much
simpler and understandable.

Oleg.

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