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

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Date:	Thu, 21 Jul 2016 14:06:50 -0700
From:	Andrew Vagin <avagin@...tuozzo.com>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
CC:	Andrey Vagin <avagin@...nvz.org>, <linux-kernel@...r.kernel.org>,
	<linux-api@...r.kernel.org>,
	<containers@...ts.linux-foundation.org>, <criu@...nvz.org>,
	<linux-fsdevel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	"W. Trevor King" <wking@...mily.us>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships
 between namespaces

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" <ebiederm@...ssion.com>
> > Cc: James Bottomley <James.Bottomley@...senPartnership.com>
> > Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
> > Cc: "W. Trevor King" <wking@...mily.us>
> > Cc: Alexander Viro <viro@...iv.linux.org.uk>
> > Cc: Serge Hallyn <serge.hallyn@...onical.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/

View attachment "0001-namespace.7-descirbe-NS_GET_USERNS-and-NS_GET-PARENT.patch" of type "text/plain" (1740 bytes)