netdev - Re: [PATCH net] failover: eliminate callback hell

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Message-ID: <CAKgT0UcJ=pbAjK6CoL8wbbqBdgeUP4xhs6uwZ0-i7X8+0Suwng@mail.gmail.com>
Date:   Thu, 7 Jun 2018 07:17:51 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <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 3:25 PM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> On Wed, 6 Jun 2018 14:54:04 -0700
> "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?
>
> DPDK drivers in 18.05 depend on 2 device model. Yes it is a bit of mess
> but that is the way it is.

Why would DPDK care what we do in the kernel? Isn't it just slapping
vfio-pci on the netdevs it sees?