Date:   Fri, 8 Jun 2018 15:54:38 -0700
From:   Siwei Liu <loseweigh@...il.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>, kys@...rosoft.com,
        haiyangz@...rosoft.com, David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH net] failover: eliminate callback hell

On Wed, Jun 6, 2018 at 2:54 PM, Samudrala, Sridhar
<sridhar.samudrala@...el.com> wrote:
>
>
> On 6/6/2018 2:24 PM, Stephen Hemminger wrote:
>>
>> On Wed, 6 Jun 2018 15:30:27 +0300
>> "Michael S. Tsirkin" <mst@...hat.com> wrote:
>>
>>> On Wed, Jun 06, 2018 at 09:25:12AM +0200, Jiri Pirko wrote:
>>>>
>>>> Tue, Jun 05, 2018 at 05:42:31AM CEST, stephen@...workplumber.org wrote:
>>>>>
>>>>> The net failover should be a simple library, not a virtual
>>>>> object with function callbacks (see callback hell).
>>>>
>>>> Why just a library? It should do a common things. I think it should be a
>>>> virtual object. Looks like your patch again splits the common
>>>> functionality into multiple drivers. That is kind of backwards attitude.
>>>> I don't get it. We should rather focus on fixing the mess the
>>>> introduction of netvsc-bonding caused and switch netvsc to 3-netdev
>>>> model.
>>>
>>> So it seems that at least one benefit for netvsc would be better
>>> handling of renames.
>>>
>>> Question is how can this change to 3-netdev happen?  Stephen is
>>> concerned about risk of breaking some userspace.
>>>
>>> Stephen, this seems to be the usecase that IFF_HIDDEN was trying to
>>> address, and you said then "why not use existing network namespaces
>>> rather than inventing a new abstraction". So how about it then? Do you
>>> want to find a way to use namespaces to hide the PV device for netvsc
>>> compatibility?
>>>
>> Netvsc can't work with 3 dev model. MS has worked with enough distro's and
>> startups that all demand eth0 always be present. And VF may come and go.
>> After this history, there is a strong motivation not to change how kernel
>> behaves. Switching to 3 device model would be perceived as breaking
>> existing userspace.
>
>
> I think it should be possible for netvsc to work with 3 dev model if the
> only
> requirement is that eth0 will always be present. With net_failover, you will
> see eth0 and eth0nsby OR with older distros eth0 and eth1.  It may be an
> issue
> if somehow there is userspace requirement that there can be only 2 netdevs,
> not 3
> when VF is plugged.
>
> eth0 will be the net_failover device and eth0nsby/eth1 will be the netvsc
> device
> and the IP address gets configured on eth0. Will this be an issue?
>
Did you realize that the eth0 name in the current 3-netdev code can't
be consistently persisted across reboot, if you have more than one VFs
to pair with? On one boot it got eth0/eth0nsby, on the next it may get
eth1/eth1nsby on the same interface.

It won't be useable by default until you add some custom udev rules.

-Siwei

>
>
>>
>> With virtio you can  work it out with the distro's yourself.
>> There is no pre-existing semantics to deal with.
>>
>> For the virtio, I don't see the need for IFF_HIDDEN.
>> With 3-dev model as long as you mark the PV and VF devices
>> as slaves, then userspace knows to leave them alone. Assuming userspace
>> is already able to deal with team and bond devices.
>> Any time you introduce new UAPI behavior something breaks.
>>
>> On the rename front, I really don't care if VF can be renamed. And for
>> netvsc want to allow the PV device to be renamed. Udev developers want
>> that
>> but have not found a stable/persistent value to expose to userspace
>> to allow it.
>
>

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