Hi,
On 14 July 2016 at 20:20, Andrey Vagin <avagin@xxxxxxxxxx> wrote:
> 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.
This looks interesting to me because I am interested in representing
in a graphical way the relationship between different mounts in
different mount namespaces (showing the ID, the parent-children
relationships, mount peer groups, the master-slave relationships etc),
specially for containers. The first idea was to take both
/proc/1/mountinfo and /proc/$OTHER_PID/mountinfo and I can correlate
the "shared:" and "master:" fields in the mountinfo files.
But I cannot read the /proc/$pid/mountinfo of mount namespaces when
there are no processes in those mount namespaces. For example, if
those mount namespaces stay alive only because they contain
"shared&slave" mounts between master mounts and slave mounts that I
can see in /proc/$pid/mountinfo. Fictional example:
# mntns 1, mountinfo 1 (visible via /proc/1/mountinfo)
61 0 253:1 / / rw shared:1
# mntns 2, mountinfo 2 (not visible via any /proc/$pid/mountinfo)
731 569 0:75 / / rw master:1 shared:42
# mntns 3, mountinfo 3 (not visible via any /proc/${container_pid}/mountinfo)
762 597 0:82 / / rw master:42 shared:76
As far as I understand, I cannot get a reference to the mntns2 fd
because mnt namespaces are not hierarchical, and I cannot get its
/proc/???/mountinfo because no processes live inside.
Is there a way around it? Should this use case be handled together?
Thanks!
Alban
> 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]:
>> 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@xxxxxxxxxxxx>
> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx>
> Cc: "W. Trevor King" <wking@xxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
>
> --
> 2.5.5
>
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