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

- From: Andrew Vagin \<hidden\>
- Date: 2016-07-21 21:06:50 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/07/109879
- Thread: https://ratatoskr.run/linux-api/2016/07/109882/t.md

```text
On Thu, Jul 21, 2016 at 04:41:12PM +0200, Michael Kerrisk (man-pages) wrote:
> Hi Andrey,
> 
> On 07/14/2016 08:20 PM, Andrey Vagin wrote:

<snip>

> 
> Could you add here an of the API in detail: what do these FDs refer to,
> and how do you use them to solve the use case? And could you you add
> that info to the commit messages please.

Hi Michael,

A patch for man-pages is attached. It adds the following text to
namespaces(7).

Since  Linux 4.X, the following ioctl(2) calls are supported for names‐
pace file descriptors.  The correct syntax is:

      fd = ioctl(ns_fd, ioctl_type);

where ioctl_type is one of the following:

NS_GET_USERNS
      Returns a file descriptor that refers to an owning  user  names‐
      pace.

NS_GET_PARENT
      Returns  a  file  descriptor  that refers to a parent namespace.
      This ioctl(2) can be used for pid and user namespaces. For  user
      namespaces,  NS_GET_PARENT and NS_GET_USERNS have the same mean‐
      ing.

In addition to generic ioctl(2) errors, the following specific ones can
occur:

EINVAL NS_GET_PARENT was called for a nonhierarchical namespace.

EPERM  The  requested  namespace  is  outside  of the current namespace
      scope.

ENOENT ns_fd refers to the init namespace.

Thanks,
Andrew

> 
> Thanks,
> 
> Michael
> 
> 
> > [1] https://lkml.org/lkml/2016/7/6/158
> > [2] https://lkml.org/lkml/2016/7/9/101
> > 
> > Cc: "Eric W. Biederman" <redacted>
> > Cc: James Bottomley <redacted>
> > Cc: "Michael Kerrisk (man-pages)" <redacted>
> > Cc: "W. Trevor King" <redacted>
> > Cc: Alexander Viro <redacted>
> > Cc: Serge Hallyn <redacted>
> > 
> > --
> > 2.5.5
> > 
> > 
> 
> 
> -- 
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
```

## Attachments

- [0001-namespace.7-descirbe-NS\_GET\_USERNS-and-NS\_GET-PARENT.patch](https://ratatoskr.run/linux-api/2016/07/109879/attachment/0) (text/plain, 1797 bytes)
- [(unnamed)](https://ratatoskr.run/linux-api/2016/07/109879/attachment/1) (text/plain, 205 bytes)