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

- List: linux-api
- 3 messages, 3 authors
- Page: https://ratatoskr.run/linux-api/2016/07/110699/t

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

- From: Michael Kerrisk (man-pages) \<hidden\>
- Date: 2016-07-22 06:48:03 
- Message: https://ratatoskr.run/linux-api/2016/07/110699.md

```text
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" <redacted>
>>> Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
>>> Cc: "Michael Kerrisk (man-pages)" <redacted>
>>> Cc: "W. Trevor King" <redacted>
>>> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
>>> 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/


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
_______________________________________________
Containers mailing list
Containers@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/containers
```

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

- From: Andrey Vagin \<hidden\>
- Date: 2016-07-22 18:25:41 
- Message: https://ratatoskr.run/linux-api/2016/07/109878.md

```text
On Thu, Jul 21, 2016 at 11:48 PM, Michael Kerrisk (man-pages)
[ref] wrote:
> 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.)

I'm sorry, but I am not sure that I understand what you ask.

Here are the origin questions:
Someone else then asked me a question that led me to wonder about
generally introspecting on the parental relationships between user
namespaces and the association of other namespaces types with user
namespaces. One use would be visualization, in order to understand the
running system. Another would be to answer the question I already
mentioned: what capability does process X have to perform operations
on a resource governed by namespace Y?

Here is an example which shows how we can get the owning namespace
inode number by using these ioctl-s.

$ ls -l /proc/13929/ns/pid
lrwxrwxrwx 1 root root 0 Jul 22 21:03 /proc/13929/ns/pid -> 'pid:[4026532228]'

$ ./nsowner /proc/13929/ns/pid
user:[4026532227]

The owning user namespace for pid:[4026532228] is user:[4026532227].

The nsowner  tool is cimpiled from this code:

int main(int argc, char *argv[])
{
        char buf[128], path[] = "/proc/self/fd/0123456789";
        int ns, uns, ret;

        ns = open(argv[1], O_RDONLY);
        if (ns < 0)
                return 1;

        uns = ioctl(ns, NS_GET_USERNS);
        if (uns < 0)
                return 1;

        snprintf(path, sizeof(path), "/proc/self/fd/%d", uns);
        ret = readlink(path, buf, sizeof(buf) - 1);
        if (ret < 0)
                return 1;
        buf[ret] = 0;

        printf("%s\n", buf);

        return 0;
}

Does this example answer to the origin question? If it isn't, could
you eloborate what you expect to see here.

And I wrote one more example which show all relationships between
namespaces. It enumirates all processes in a system, collects all
namespaces and determins parent and owning namespaces for each of
them, then it constructs a namespace tree and shows it.

Here is a code: https://gist.github.com/avagin/db805f95e15ffb0af7e559dbb8de4418

Here is an example of output for my test system:
[root@fc24 nsfs]# ./nstree
user:[4026531837]
 \__  mnt:[4026532203]
 \__  ipc:[4026531839]
 \__  user:[4026532224]
     \__  user:[4026532226]
         \__  user:[4026532227]
             \__  pid:[4026532228]
     \__  pid:[4026532225]
         \__  pid:[4026532228]
 \__  user:[4026532221]
     \__  pid:[4026532222]
     \__  user:[4026532223]
 \__  mnt:[4026532211]
 \__  uts:[4026531838]
 \__  cgroup:[4026531835]
 \__  pid:[4026531836]
     \__  pid:[4026532225]
         \__  pid:[4026532228]
     \__  pid:[4026532222]
 \__  mnt:[4026531857]
 \__  mnt:[4026531840]
 \__  net:[4026531957]

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 <James.Bottomley@HansenPartnership.com>
>>>> Cc: "Michael Kerrisk (man-pages)" <redacted>
>>>> Cc: "W. Trevor King" <redacted>
>>>> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
>>>> 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/
>
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/containers
_______________________________________________
Containers mailing list
Containers@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/containers
```

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

- From: Michael Kerrisk (man-pages) \<hidden\>
- Date: 2016-07-25 11:48:03 
- Message: https://ratatoskr.run/linux-api/2016/07/109870.md

```text
Hi Andrey,

On 07/22/2016 08:25 PM, Andrey Vagin wrote:
> On Thu, Jul 21, 2016 at 11:48 PM, Michael Kerrisk (man-pages)
> [ref] wrote:
>> 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.

For each of the above, I think it is worth mentioning that the
close-on-exec flag is set for the returned file descriptor.

>>>
>>> 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.

Perhaps add "and the caller does not have CAP_SYS_ADMIN" in the initial
user namespace"?

>>>
>>> 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.)
>
> I'm sorry, but I am not sure that I understand what you ask.
>
> Here are the origin questions:
> Someone else then asked me a question that led me to wonder about
> generally introspecting on the parental relationships between user
> namespaces and the association of other namespaces types with user
> namespaces. One use would be visualization, in order to understand the
> running system. Another would be to answer the question I already
> mentioned: what capability does process X have to perform operations
> on a resource governed by namespace Y?
>
> Here is an example which shows how we can get the owning namespace
> inode number by using these ioctl-s.
>
> $ ls -l /proc/13929/ns/pid
> lrwxrwxrwx 1 root root 0 Jul 22 21:03 /proc/13929/ns/pid -> 'pid:[4026532228]'
>
> $ ./nsowner /proc/13929/ns/pid
> user:[4026532227]
>
> The owning user namespace for pid:[4026532228] is user:[4026532227].
>
> The nsowner  tool is cimpiled from this code:
>
> int main(int argc, char *argv[])
> {
>         char buf[128], path[] = "/proc/self/fd/0123456789";
>         int ns, uns, ret;
>
>         ns = open(argv[1], O_RDONLY);
>         if (ns < 0)
>                 return 1;
>
>         uns = ioctl(ns, NS_GET_USERNS);
>         if (uns < 0)
>                 return 1;
>
>         snprintf(path, sizeof(path), "/proc/self/fd/%d", uns);
>         ret = readlink(path, buf, sizeof(buf) - 1);
>         if (ret < 0)
>                 return 1;
>         buf[ret] = 0;
>
>         printf("%s\n", buf);
>
>         return 0;
> }

So, from my point of view, the important piece that was missing from
your commit message was the note to use readlink("/proc/self/fd/%d")
on the returned FDs. I think that detail needs to be part of the
commit message (and also the man page text). I think it even be
helpful to include the above program as part of the commit message:
it helps people more quickly grasp the API.

> Does this example answer to the origin question?

Yes.

>If it isn't, could
> you eloborate what you expect to see here.
>
> And I wrote one more example which show all relationships between
> namespaces. It enumirates all processes in a system, collects all
> namespaces and determins parent and owning namespaces for each of
> them, then it constructs a namespace tree and shows it.
>
> Here is a code: https://gist.github.com/avagin/db805f95e15ffb0af7e559dbb8de4418

That's great! Thanks!
 
> Here is an example of output for my test system:
> [root@fc24 nsfs]# ./nstree
> user:[4026531837]
>  \__  mnt:[4026532203]
>  \__  ipc:[4026531839]
>  \__  user:[4026532224]
>      \__  user:[4026532226]
>          \__  user:[4026532227]
>              \__  pid:[4026532228]
>      \__  pid:[4026532225]
>          \__  pid:[4026532228]
>  \__  user:[4026532221]
>      \__  pid:[4026532222]
>      \__  user:[4026532223]
>  \__  mnt:[4026532211]
>  \__  uts:[4026531838]
>  \__  cgroup:[4026531835]
>  \__  pid:[4026531836]
>      \__  pid:[4026532225]
>          \__  pid:[4026532228]
>      \__  pid:[4026532222]
>  \__  mnt:[4026531857]
>  \__  mnt:[4026531840]
>  \__  net:[4026531957]

Cheers,

Michael

>>>>> [1] https://lkml.org/lkml/2016/7/6/158
>>>>> [2] https://lkml.org/lkml/2016/7/9/101

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