Re: [PATCH] [RFC] c/r: Add UTS support

[Mike Waychison <mikew-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>]

Serge E. Hallyn wrote:
> Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org):
>> Ok.  I see what you are trying to accomplish with this and honestly I
>> think it is silly.
>>
>> We should start the threads we need in the kernel, and if we need to
>> run clone_pid fine.  I am not comfortable exporting clone_with_pid to
>> user space.
> 
> Even if we create the task tree in userspace, I don't see why we
> can't have the parent of each nested pid_ns pass CLONE_NEWPID to
> clone_with_pid() instead of doing clone first and then unsharing
> the pidns?
> 
> As for clone_with_pid(), I don't particularly like the semantics,
> but as was discussed over IRC, we could have clone_with_pid()
> return -EINVAL unless it is called while it is called from a task
> inside a restarting container.  (and -EPERM if setting a pid in
> a pid_ns which was not created as part of the container)  Eric
> do you dislike that any less?

Wouldn't this mean the kernel would have to track which namespaces are 
part of a restart and which aren't?   Seems a little kludgy to me.

> 
>> As for the implementation of allocating a struct pid with a certain
>> set of pid values.  I expect we can do that easily enough by
>> refactoring the pid allocator to be passed in the min/max pid to
>> allocate from, and have a special case that passes in a different set
>> of min/max values so we can allocate just the pid we need.
> 
> What is wrong with Alexey's patch, which simply passes in the values
> themselves?  Do you have another use in mind for the min/max pid
> values?
> 
>> If the primary use for a userspace interface is restart I feel we are
>> doing it wrong.
> 
> I think that's a good guideline, bad rule.  Certainly possible
> that you're right that this is just pointing to in-kernel
> recreation of process tree as the way to go.  I was getting
> that feeling myself, but then there are still very good reasons
> not to do that, as there are things which each task should do
> before completing sys_restart() which are best done in userspace.
> These include for instance creating virtual nics, and calling
> Oren's suggested 'cr_advise()' system calls.
> 
> -serge