netdev - Re: [RFC PATCH 2/3] netdev: kernel-only IFF

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Date:   Wed, 4 Apr 2018 01:01:37 -0700
From:   Siwei Liu <loseweigh@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     David Ahern <dsahern@...il.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        David Miller <davem@...emloft.net>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        Jakub Kicinski <kubakici@...pl>,
        Jason Wang <jasowang@...hat.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org
Subject: Re: [RFC PATCH 2/3] netdev: kernel-only IFF_HIDDEN netdevice

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