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SubjectRe: RFC: Multiple instances of kernel namespaces.
On Sat, Jan 21, 2006 at 03:04:16AM -0700, Eric W. Biederman wrote:
> "Serge E. Hallyn" <serue@us.ibm.com> writes:
>
> > Quoting Eric W. Biederman (ebiederm@xmission.com):
> >>
> >> At this point I have to confess I have been working on something
> >> similar, to IBM's pid virtualization work. But I have what is at
> >> least for me a unifying concept, that makes things easier to think
> >> about.
> >>
> >> The idea is to think about things in terms of namespaces. Currently
> >> in the kernel we have the fs/mount namespace already implemented.
> >>
> >> Partly this helps on what the interface for creating a new namespace
> >> instance should be. 'clone(CLONE_NEW<NAMESPACE_TYPE>)', and how
> >> it should be managed from the kernel data structures.
> >>
> >> Partly thinking of things as namespaces helps me scope the problem.
> >>
> >> Does this sound like a sane approach?
> >
> > And a bonus of this is that for security and vserver-type applications,
> > the CLONE_NEWPID and CLONE_NEWFS will often happen at the same time.
> >
> > How do you (or do you?) address naming namespaces? This would be
> > necessary for transitioning into an existing namespace, performing
> > actions on existing namespaces (i.e. checkpoint, migrate to another
> > machine, enter the namespace and kill pid 521), and would just be
> > useful for accounting purposes, i.e. how else do you have a
> > "ps --all-namespaces" specify a process' namespace?
>
> So I address naming indirectly. The last thing I want to have
> is to add yet another namespace to the kernel for naming namespaces.
> We have enough namespaces already.
>
> In any sane context for a pid-namespace we need a pid that
> we can call waitpid on, so we don't break the process tree.
> Which means at least the init process has 2 pids, one
> that it's parent sees, and another (1) that it and it's
> children see.
>
> So I name pidspaces like we do sessions of process groups
> and sessions by the pid of the leader.
>
> So in the simple case I have names like:
> 1178/1632

which is a new namespace in itself, but it doesn't matter
as long as it uniquely and persistently identifies the
namespace for the time it exists ... just leaves the
question how to retrieve a list of all namespaces :)

> > Doubt we want to add an argument to clone(), so do we just add a new
> > proc, sysfs, or syscall for setting a pid-namespace name?
>
> That shouldn't be necessary.
>
> > Do we need a new syscall for transitioning into an existing namespace?
>
> That is a good question. The FS namespaces that we already have
> has much the same problem. A completely different solution to
> this problem seems to have been implemented but I don't grasp it
> yet.
>
> Inherently transitioning to an existing namespace is something
> that is straight forward to implement, so it is worth thinking
> about.
>
> If I want a guest that can keep secrets from the host sysadmin I don't
> want transitioning into a guest namespace to come too easily.

which can easily be achieved by 'marking' the namespace
as private and/or applying certain rules/checks to the
'enter' procedure ...

best,
Herbert

> Currently I can always just create an extra child of pid 1
> that I will be my slave. The problem is that this is an extra
> process laying around.
>
> Eric
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