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Subject: Re: [RFC PATCH 2/3] netdev: kernel-only IFF_HIDDEN netdevice

On Tue, Apr 3, 2018 at 11:19 PM, Jiri Pirko <jiri@resnulli.us> wrote:
> Wed, Apr 04, 2018 at 03:04:26AM CEST, dsahern@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

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.


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