Re: [RFC][PATCH 0/20] Multiple instances of the process id namespace

[Hubertus Franke <frankeh@watson.ibm.com>]

Eric W. Biederman wrote:
> There have been several discussions in the past month about how
> to do a good job of implementing a subset of user space that
> looks like it has the system to itself.  Essentially making
> chroot everything it could be.  This is my take on what
> the implementation of a pid namespace should look like.
> 

Eric, this looks very good. The pspace internal implementation
is very similar to what I was working on objectifying the pidmap
etc. I was pursuing the same route in using find_pid()
functions as the means to distinguish pspaces rather then
actually virtualizing them.

But this code already goes so much further in many many aspects.
Kudos to you.
I am still going through some of the details, but this is an
excellent starting position.

> 
> What follows is a real patch set that is sufficiently complete
> to be used and useful in it's own right.  There are a few areas
> of the kernel where the patchset does not reach, mostly these
> cause the compile to fail.  In addition a good thorough review
> still needs to be done.  This patchset does paint a picture
> of how I think things should look.
> 
> From the kernel community at large I am asking:
>   Does the code look generally sane?

Yes, but I have one question for you...
Large parts of the patch are adding the pspace argument
to find_task_by_pid() and in many cases that argument is
current->pspace.
It might bring down the size of the patch if you
have

find_task_by_pid( pid )  {  return find_task_pidspace_by_pid ( current->pspace, pid ); }

and then only deal with the exceptional cases using find_task_pidspace_by_pid
when the pidspace is different..

> 
>   Does the use of clone to create a new namespace instance look
>   like the sane approach?
> 

At he surface it looks OK .. how does this work in a multi-threaded
process which does cloen ( CLONE_NPSPACE ) ?
We discussed at some point that exec is the right place to do it,
but what I get is that because this is the container_init task
we are OK !
A bit clarification would help here ...

> Hopefully this code is sufficiently comprehensible to allow a good
> discussion to come out of this.
> 

Yes

> Thanks for your time,
> 
> Eric

-- Hubertus