Re: [RFC PATCH] proc, pidns: Add highpid

From: Pavel Emelyanov
Date: Mon Dec 01 2014 - 07:34:04 EST

On 12/01/2014 09:47 AM, Florian Weimer wrote:
> * Andy Lutomirski:
>> On Nov 30, 2014 1:47 AM, "Florian Weimer" <fw@xxxxxxxxxxxxx> wrote:
>>> * Andy Lutomirski:
>>>> The initial implementation is straightforward: highpid is simply a
>>>> 64-bit counter. If a high-end system can fork every 3 ns (which
>>>> would be amazing, given that just allocating a pid requires at
>>>> atomic operation), it would take well over 1000 years for highpid to
>>>> wrap.
>>> I'm not sure if I'm reading the patch correctly, but is the counter
>>> namespaced? If yes, why?
>> It's namespaced so that CRIU can migrate/restore a whole pid namespace.
> Oh well, this requirement is at odds with system-wide uniqueness. Is
> CRIU really that important? :-)

Well, in this context it is. Since the main (if not the only) use-case for
highpid is to read one, remember, then compare to new value, restoring it
to wrong/arbitrary value will break the using applications in 100% cases.

Thus we really need the ability to restore this value.


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