Andrey Vagin [off-list ref] writes:

Hello,

I forgot to add --cc-cover for git send-email, so everyone who is in
Cc got only a cover letter. All messages were sent in mail lists.

Sorry for inconvenience.

Mostly the code looked sensible.  But I had a couple of issues.
Resend this in September (when the merge window is closed and I am back
from vacation) and I will give this a thorough review and get this
merged.  Or possibly next week if Linus releases another -rc

On Thu, Jul 14, 2016 at 11:20 AM, Andrey Vagin [off-list ref] wrote:

quoted

Each namespace has an owning user namespace and now there is not way
to discover these relationships.

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

Why we may want to know relationships between namespaces?

One use would be visualization, in order to understand the running system.
Another would be to answer the question: what capability does process X have to
perform operations on a resource governed by namespace Y?

One more use-case (which usually called abnormal) is checkpoint/restart.
In CRIU we age going to dump and restore nested namespaces.

There [1] was a discussion about which interface to choose to determing
relationships between namespaces.

Eric suggested to add two ioctl-s [2]:

quoted

Grumble, Grumble.  I think this may actually a case for creating ioctls
for these two cases.  Now that random nsfs file descriptors are bind
mountable the original reason for using proc files is not as pressing.

One ioctl for the user namespace that owns a file descriptor.
One ioctl for the parent namespace of a namespace file descriptor.

Here is an implementaions of these ioctl-s.

[1] https://lkml.org/lkml/2016/7/6/158
[2] https://lkml.org/lkml/2016/7/9/101

Cc: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: James Bottomley <James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>
Cc: "Michael Kerrisk (man-pages)" <redacted>
Cc: "W. Trevor King" <redacted>
Cc: Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: Serge Hallyn <redacted>

Eric