Virtualization - Apr 2018 - [RFC PATCH 2/3] netdev: kernel-only IFF_HIDDEN netdevice

Wed, Apr 04, 2018 at 03:04:26AM CEST, dsahern at gmail.com
wrote:
>On 4/3/18 9:42 AM, Jiri Pirko wrote:
>>>
>>> There are other use cases that want to hide a device from
userspace. I
>> 
>> What usecases do you have in mind?
>
>As mentioned in a previous response some kernel drivers create control
>netdevs. Just as in this case users should not be mucking with it, and
virtio_net. Any other drivers?

>S/W like lldpd should ignore it.
It's just a matter of identification of the netdevs, so the user knows
what to do.

>
>> 
>>> would prefer a better solution than playing games with name
prefixes and
>>> one that includes an API for users to list all devices -- even ones
>>> hidden by default.
>> 
>> Netdevice hiding feels a bit scarry for me. This smells like a
workaround
>> for userspace issues. Why can't the netdevice be visible always and
>> userspace would know what is it and what should it do with it?
>> 
>> Once we start with hiding, there are other things related to that which
>> appear. Like who can see what, levels of visibility etc...
>> 
>
>I would not advocate for any API that does not allow users to have full
>introspection. The intent is to hide the netdev by default but have an
>option to see it.
As an administrator, I want to see all by default. I think it is
reasonable requirements. Again, this awfully smells like a workaround...

On Tue, Apr 3, 2018 at 11:19 PM, Jiri Pirko <jiri at resnulli.us>
wrote:
> Wed, Apr 04, 2018 at 03:04:26AM CEST, dsahern at gmail.com wrote:
>>On 4/3/18 9:42 AM, Jiri Pirko wrote:
>>>>
>>>> There are other use cases that want to hide a device from
userspace. I
>>>
>>> What usecases do you have in mind?
>>
>>As mentioned in a previous response some kernel drivers create control
>>netdevs. Just as in this case users should not be mucking with it, and
>
> virtio_net. Any other drivers?
netvsc if factoring out virtio_bypass to a common driver.
>
>
>>S/W like lldpd should ignore it.
>
> It's just a matter of identification of the netdevs, so the user knows
> what to do.
>
>
>>
>>>
>>>> would prefer a better solution than playing games with name
prefixes and
>>>> one that includes an API for users to list all devices -- even
ones
>>>> hidden by default.
>>>
>>> Netdevice hiding feels a bit scarry for me. This smells like a
workaround
>>> for userspace issues. Why can't the netdevice be visible always
and
>>> userspace would know what is it and what should it do with it?
>>>
>>> Once we start with hiding, there are other things related to that
which
>>> appear. Like who can see what, levels of visibility etc...
>>>
>>
>>I would not advocate for any API that does not allow users to have full
>>introspection. The intent is to hide the netdev by default but have an
>>option to see it.
>
> As an administrator, I want to see all by default. I think it is
> reasonable requirements. Again, this awfully smells like a workaround...
If the requirement is just for dumping the link info i.e. perform
read-only operation on the hidden netdev, it's completely fine.
However, I am not a big fan of creating a weird mechanism to allow
user deliberately manipulate the visibility (hide/unhide) of a netdev
in any case at any time. This is subject to becoming a slippery slope
to work around any software issue that should get fixed in the right
place.

Let's treat IFF_HIDDEN as a means to hide auto-managed netdevices. If
it's just the name is misleading, I can get it renamed to something
like IFF_AUTO_MANAGED which might reflect its nature more properly.

Thanks,
-Siwei