Re: Virtualizing /proc/sys/kernel/random/boot_id per container ?

[Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>]

On 08/31/2012 04:13 AM, Eric W. Biederman wrote:
> "Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:
> 
>> On Thu, Aug 30, 2012 at 03:15:17PM -0700, Eric W. Biederman wrote:
>>> "Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:
>>>
>>>> One of the features that SystemD folks have asked us to fix in LXC, is
>>>> to make sure that /proc/sys/kernel/random/boot_id changes each time a
>>>> container is started.
>>>
>>> There may be a good reason for this.  Most of the time what I have seen
>>> of kernel requests from the direction of SystemD is that while there may
>>> be a real problem but usually their imagined solution is not a
>>> particularly good solution.  So a description of the problem is needed.
>>>
>>> Justifying something with just SystemD wants this is a good way to get
>>> a nack.
>>
>> SystemD records log messages for all system services in their journal.
>> They can show you all log messages for the current service execution,
>> all log messages for a service since system boot, or all log messsages
>> ever. The boot_id value is used as a unique tag to allow grouping of
>> the log messages per system boot. When we run systemd inside a container
>> we want to get that grouping of log messages generated by services inside
>> the container, to take account of the container boot, not the host boot.
>> Hence the desire to have the boot_id value reflect when a container is
>> booted.
> 
> Since SystemD post-dates containers and since the logging feature is not
> currently in wide use that use case is completely non-persuasive.
> 
> So far this just sounds like a plain SystemD bug and something that can
> be easily changed at this point in time.
> 
> It has been a long time but my fuzzy memory says that the originial
> boot_id justification was based on use cases that could not be solved
> any other way.
> 
> My memory says it was this thread https://lkml.org/lkml/1999/5/31/233
> that inspired the implementation of boot_id.  However reading the
> current emacs source code it appears emacs gave up before boot_id
> was implemented and stats /var/run/random-seed (which we seem to
> have removed) or looks in wtmp or utmp for the latest boot record.
> 
> I did a quick grep through the binaries on my system and I could not
> find anything using /proc/sys/random/boot_id.
> 
> That suggests to me that the proper solution is to actually just remove
> boot_id.
> 
> Hmm.  And then there is other interesting detail.  What should boot_id
> return after the processes have migrated from one system to another.
> 

Since this would be a per-boot id, this clearly has to be carried over
with migration, along with all the tons of data we already carry.