Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces

On Sat, 2016-07-23 at 14:14 -0700, W. Trevor King wrote:

On Thu, Jul 14, 2016 at 11:20:14AM -0700, Andrey Vagin wrote:

quoted

Pid and user namepaces are hierarchical. There is no way to 
discover parent-child relationships too.

It bothers me that network namespaces are not hierarchical too ;).

Well, there's a reason for that: mapping namespaces need to be be
hierarchical because the mapping may be remapped; The initial point for
creating a new namespace is the mapped endpoint of the old one.  Label
based namespaces don't really have any need to be.

namespaces(7) and clone(2) both have:

  When a network namespace is freed (i.e., when the last process in
  the namespace terminates), its physical network devices are moved
  back to the initial network namespace (not to the parent of the
  process).

So the initial network namespace (the head of net_namespace_list?) is
special [1].  To understand how physical network devices will be
handled, it seems like we want to treat network devices as a depth-1
tree, with all non-initial net namespaces as children of the initial
net namespace.  Can we extend this series' NS_GET_PARENT to return:

* EPERM for an unprivileged caller (like this series currently does
  for PID namespaces),
* ENOENT when called on net_namespace_list, and
* net_namespace_list when called on any other net namespace.

What's the practical application of this?  independent net namespaces
are managed by the ip netns command.  It pins them by a bind mount in a
flat fashion; if we make them hierarchical the tool would probably need
updating to reflect this, so we're going to need a reason to give the
network people.  Just having the interfaces not go back to root when
you do an ip netns delete doesn't seem very compelling.

James