[Devel] Re: [RFC] [PATCH 0/3] containers: introduction

[Serge E. Hallyn]

Quoting Eric W. Biederman (ebiederm at xmission.com):
> "Serge E. Hallyn" <serue at us.ibm.com> writes:
> 
> > Following is a small patchset implementing what I was describing
> > about earlier, namely semantics for a hierarchical container
> > naming scheme.
> >
> > What works:
> >
> > 	1.  ls -l /proc/$$/container
> > 	  shows the full hierarchical name of the container;
> >
> > 	2.  mount -t containerfs none /container
> > 	  results in a file tree under /container representing the
> > 	  full container hierarchy
> >
> > 	3.  cd /proc/$$/container; ls
> > 	  results in a listing of child containers
> >
> > What doesn't work:
> > 	1. The /proc/$$/container link always appears dead (red
> > 	in bash on my fedora test system) because it points
> > 	into a kern_mounted fs.
> 
> Just a quick comment.  I am not at all comfortable exporting
> internal kernel mounts without something explicit happening.
> I played with that in one of my earlier patches and the corner cases
> are just extremely weird and mess with the usual unix guarantees
> about the namespace.  Two specific examples are that .. fails to work properly,
> as does sys_getcwd.
> 
> My gut feel is that we need something like union mounts so we can
> glue these kinds of things but that will mount and unmount as
> a unit.  So we can preserve backwards compatibility with existing
> filesystems.  I haven't had a chance to look at what it would
> take to implement this kind of hidden union mount though.

Or we could go ahead and fully implement it in procfs.  As you'd said
earlier, that really maps best into what we want.  Containerfs was
just much simpler and quicker to implement for demonstrating the semantics.

> With the mount tree cloning code I believe we are quite close (at least
> if we don't need the union property).
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