linux-kernel - Re: device namespaces

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Date:   Wed, 9 Jun 2021 09:54:05 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        gregkh@...uxfoundation.org, containers@...ts.linux.dev,
        linux-kernel@...r.kernel.org, lkml@...ux.net
Subject: Re: device namespaces

On 6/9/21 9:21 AM, Christian Brauner wrote:
> On Wed, Jun 09, 2021 at 09:02:36AM +0200, Hannes Reinecke wrote:
>> On 6/9/21 8:38 AM, Christian Brauner wrote:
>>> On Tue, Jun 08, 2021 at 12:16:43PM -0500, Eric W. Biederman wrote:
>>>> Hannes Reinecke <hare@...e.de> writes:
>>>>
>>>>> On 6/8/21 4:29 PM, Christian Brauner wrote:
>>>>>> On Tue, Jun 08, 2021 at 04:10:08PM +0200, Hannes Reinecke wrote:
>> [ .. ]
>>>>> Granted, modifying sysfs layout is not something for the faint-hearted,
>>>>> and one really has to look closely to ensure you end up with a
>>>>> consistent layout afterwards.
>>>>>
>>>>> But let's see how things go; might well be that it turns out to be too
>>>>> complex to consider. Can't tell yet.
>>>>
>>>> I would suggest aiming for something like devptsfs without the
>>>> complication of /dev/ptmx.
>>>>
>>>> That is a pseudo filesystem that has a control node and virtual block
>>>> devices that were created using that control node.
>>>
>>> Also see android/binder/binderfs.c
>>>
>> Ah. Will have a look.
> 
> I implemented this a few years back and I think it should've made it
> onto Android by default now. So that approach does indeed work well, it
> seems:
> https://chromium.googlesource.com/aosp/platform/system/core/+/master/rootdir/init.rc#257
> 
> This should be easier to follow than the devpts case because you don't
> need to wade through the {t,p}ty layer.
> 
>>
>>>>
>>>> That is the cleanest solution I know and is not strictly limited to use
>>>> with containers so it can also gain greater traction.  The interaction
>>>> with devtmpfs should be simply having devtmpfs create a mount point for
>>>> that filesystem.
>>>>
>>>> This could be a new cleaner api for things like loopback devices.
>>>
>>> I sent a patchset that implemented this last year.
>>>
>> Do you have a pointer/commit hash for this?
> 
> Yes, sure:
> https://lore.kernel.org/linux-block/20200424162052.441452-1-christian.brauner@ubuntu.com/
> 
> You can also just pull my branch. I think it's still based on v5.7 or sm:
> https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=loopfs
> 
> I'm happy to collaborate on this too.
>
How _very_ curious. 'kernfs: handle multiple namespace tags' and 'loop:
preserve sysfs backwards compability' are essentially the same patches I
did for my block namespaces prototyp; I named it 'KOBJ_NS_TYPE_BLK', not
'KOBJ_NS_TYPE_USER', though :-)

Guess we really should cooperate.

Speaking of which: why did you name it 'user' namespace?
There already is a generic 'user_namespace' in
include/linux/user_namespace.h, serving as a container for all
namespaces; as such it probably should include this 'user' namespace,
leading to quite some confusion.

Or did I misunderstood something here?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@...e.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer