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

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Date:   Wed, 6 Jun 2018 15:25:16 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>, kys@...rosoft.com,
        haiyangz@...rosoft.com, davem@...emloft.net,
        netdev@...r.kernel.org, Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH net] failover: eliminate callback hell

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.