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

[Michael Kerrisk (man-pages)]

Hi Andrey,

On 07/21/2016 11:06 PM, Andrew Vagin wrote:
> 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 for this. But still part of the question remains unanswered.
How do we (in user-space) use the file descriptors to answer any of
the questions that this patch series was designed to solve? (This
info should be in the commit message and the man-pages patch.)

Thanks,

Michael


>>> [1] https://lkml.org/lkml/2016/7/6/158
>>> [2] https://lkml.org/lkml/2016/7/9/101
>>>
>>> Cc: "Eric W. Biederman" <ebiederm at xmission.com>
>>> Cc: James Bottomley <James.Bottomley at HansenPartnership.com>
>>> Cc: "Michael Kerrisk (man-pages)" <mtk.manpages at gmail.com>
>>> Cc: "W. Trevor King" <wking at tremily.us>
>>> Cc: Alexander Viro <viro at zeniv.linux.org.uk>
>>> Cc: Serge Hallyn <serge.hallyn at canonical.com>
>>>
>>> --
>>> 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/


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/