netdev - Re: [RFC PATCH v3 0/3] Enable virtio_net to act as a backup for a passthru device

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Date:   Tue, 27 Feb 2018 09:27:18 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jakub Kicinski <kubakici@...pl>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Jason Wang <jasowang@...hat.com>,
        Siwei Liu <loseweigh@...il.com>
Subject: Re: [RFC PATCH v3 0/3] Enable virtio_net to act as a backup for a
 passthru device

Tue, Feb 27, 2018 at 02:18:12AM CET, mst@...hat.com wrote:
>On Mon, Feb 26, 2018 at 05:02:18PM -0800, Stephen Hemminger wrote:
>> On Mon, 26 Feb 2018 08:19:24 +0100
>> Jiri Pirko <jiri@...nulli.us> wrote:
>> 
>> > Sat, Feb 24, 2018 at 12:59:04AM CET, stephen@...workplumber.org wrote:
>> > >On Thu, 22 Feb 2018 13:30:12 -0800
>> > >Alexander Duyck <alexander.duyck@...il.com> wrote:
>> > >  
>> > >> > Again, I undertand your motivation. Yet I don't like your solution.
>> > >> > But if the decision is made to do this in-driver bonding. I would like
>> > >> > to see it baing done some generic way:
>> > >> > 1) share the same "in-driver bonding core" code with netvsc
>> > >> >    put to net/core.
>> > >> > 2) the "in-driver bonding core" will strictly limit the functionality,
>> > >> >    like active-backup mode only, one vf, one backup, vf netdev type
>> > >> >    check (so noone could enslave a tap or anything else)
>> > >> > If user would need something more, he should employ team/bond.    
>> > >
>> > >Sharing would be good, but netvsc world would really like to only have
>> > >one visible network device.  
>> > 
>> > Why do you mind? All would be the same, there would be just another
>> > netdevice unused by the vm user (same as the vf netdev).
>> > 
>> 
>> I mind because our requirement is no changes to userspace.
>> No special udev rules, no bonding script, no setup.
>
>Agreed. It is mostly fine from this point of view, except that you need
>to know to skip the slaves.  Maybe we could look at some kind of
>trick e.g. pretending link is down for slaves?

:O Another hack. Please, don't.


>
>> Things like cloudinit running on current distro's expect to see a single
>> eth0.  The VF device show up can also be an issue because distro's have
>> stupid rules like Network Manager trying to start DHCP on every interface.
>> We deal with that now by doing stuff like udev rules to get it to stop
>> but that is still causing user errors.

So that means that with an extra netdev for "virtio_net bypass" you will
face exactly the same problems. Should not be an issue for you then.


>
>So the ideal of a single net device isn't achieved by netvsc.
>
>Since you have scripts to skip the PT device, can't they
>hind the PV slave too? How do they identify the device to skip?
>
>I agree it would be nice to have a way to hide the extra netdev
>from userspace.

"A hidden netdevice", hmm. I believe that instead of doing hacks like
this, we should fix userspace to treat particular netdevices correctly.


>
>The benefit of the separation is that each slave device can
>be configured with e.g. its own native ethtool commands for
>optimum performance.
>
>-- 
>MST