On 09/04/2012 07:25 PM, Serge Hallyn wrote: > Quoting Glauber Costa (glommer@xxxxxxxxxxxxx): >> On 09/04/2012 06:44 PM, Serge Hallyn wrote: >>> Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx): >>>> Glauber Costa <glommer@xxxxxxxxxxxxx> writes: >>>> >>>>> On 08/31/2012 04:13 AM, Eric W. Biederman wrote: >>>>>> "Daniel P. Berrange" <berrange@xxxxxxxxxx> writes: >>>>>> >>>>>>> On Thu, Aug 30, 2012 at 03:15:17PM -0700, Eric W. Biederman wrote: >>>>>>>> "Daniel P. Berrange" <berrange@xxxxxxxxxx> 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. >>>> >>>> The twist of course is what does a boot mean. If we are really after >>>> machine boots than the current behavior is correct. >>>> >>>> Looking back in the archives the desired behavior appears to be a value >>>> that can be used to see if a pid value must be stale. >>>> >>>> As a stale pid detector boot_id is pretty lousy. Pids can still be >>>> reused. >>>> >>>> Still a role as a stale pid detector makes it clear which namespace >>>> boot_id should be in and how we should treat boot_id upon migration. >>>> >>>> You can only serve as a stale pid detector if you are in the pid >>>> namespace. >>>> >>>> So at this point patches are welcome. Hopefully with a summary >>>> of the discussion. >>> >>> I don't understand why this should be provided by the kernel. Especially >>> given that we've proven that everyone really wants this to be per-container >>> as well. >>> >>> So why not just have init, on startup, create a /run/boot_id file, perhaps >>> by sha1summing the time at which it started perhaps plus some nonce? >>> >> Why shouldn't it provided by the kernel?, is the real question > > Because it's not the right place. The origin of this thread proves that > people want a per-init, not per-kernel, value. > Not all files provided by the kernel are "per-kernel". /proc/self is full of per-namespace stuff. >> The way I see it, every file we need to setup from the outside is a >> hassle. Among many other things, it is just asking for duplication of >> efforts among multiple userspaces. >> >> netns does this for its proc files. The only reason we don't do it for >> cgroups-driven file, is that the semantics is very ill-defined. For this >> file, it doesn't seem to be the case. > > But it is the case. How do you intend to have the kernel decide what > value to put in there for a process in a container, or in a chroot? > one value per pidns. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
