netdev - Re: [PATCH net-next 0/2] Enable virtio to act as a master for a passthru device

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Date:   Tue, 2 Jan 2018 18:16:03 -0800
From:   Jakub Kicinski <kubakici@...pl>
To:     jesse.brandeburg@...el.com
Cc:     Sridhar Samudrala <sridhar.samudrala@...el.com>, mst@...hat.com,
        stephen@...workplumber.org, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org,
        Alexander Duyck <alexander.h.duyck@...el.com>
Subject: Re: [PATCH net-next 0/2] Enable virtio to act as a master for a
 passthru device

On Tue,  2 Jan 2018 16:35:36 -0800, Sridhar Samudrala wrote:
> This patch series enables virtio to switch over to a VF datapath when a VF
> netdev is present with the same MAC address. It allows live migration of a VM
> with a direct attached VF without the need to setup a bond/team between a
> VF and virtio net device in the guest.
> 
> The hypervisor needs to unplug the VF device from the guest on the source
> host and reset the MAC filter of the VF to initiate failover of datapath to
> virtio before starting the migration. After the migration is completed, the
> destination hypervisor sets the MAC filter on the VF and plugs it back to
> the guest to switch over to VF datapath.
> 
> It is based on netvsc implementation and it may be possible to make this code 
> generic and move it to a common location that can be shared by netvsc and virtio.
> 
> This patch series is based on the discussion initiated by Jesse on this thread.
> https://marc.info/?l=linux-virtualization&m=151189725224231&w=2

How does the notion of a device which is both a bond and a leg of a
bond fit with Alex's recent discussions about feature propagation?
Which propagation rules will apply to VirtIO master?  Meaning of the
flags on a software upper device may be different.  Why muddy the
architecture like this and not introduce a synthetic bond device?