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SubjectRe: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces
Hi Andrey,

On 07/14/2016 08:20 PM, Andrey Vagin 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.
> 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.

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.



> [1]
> [2]
> Cc: "Eric W. Biederman" <>
> Cc: James Bottomley <>
> Cc: "Michael Kerrisk (man-pages)" <>
> Cc: "W. Trevor King" <>
> Cc: Alexander Viro <>
> Cc: Serge Hallyn <>
> --
> 2.5.5

Michael Kerrisk
Linux man-pages maintainer;
Linux/UNIX System Programming Training:

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