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

[Pavel Emelyanov <xemul@parallels.com>]

On 12/01/2014 09:47 AM, Florian Weimer wrote:
> * Andy Lutomirski:
> 
>> On Nov 30, 2014 1:47 AM, "Florian Weimer" <fw@deneb.enyo.de> 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.

Thanks,
Pavel