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

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Message-ID: <20180223223802.GA2010@nanopsycho>
Date:   Fri, 23 Feb 2018 23:38:02 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Siwei Liu <loseweigh@...il.com>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jakub Kicinski <kubakici@...pl>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        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>
Subject: Re: [RFC PATCH v3 0/3] Enable virtio_net to act as a backup for a
 passthru device

Fri, Feb 23, 2018 at 11:22:36PM CET, loseweigh@...il.com wrote:

[...]

>>>
>>> No, that's not what I was talking about of course. I thought you
>>> mentioned the upgrade scenario this patch would like to address is to
>>> use the bypass interface "to take the place of the original virtio,
>>> and get udev to rename the bypass to what the original virtio_net
>>> was". That is one of the possible upgrade paths for sure. However the
>>> upgrade path I was seeking is to use the bypass interface to take the
>>> place of original VF interface while retaining the name and network
>>> configs, which generally can be done simply with kernel upgrade. It
>>> would become limiting as this patch makes the bypass interface share
>>> the same virtio pci device with virito backup. Can this bypass
>>> interface be made general to take place of any pci device other than
>>> virtio-net? This will be more helpful as the cloud users who has
>>> existing setup on VF interface don't have to recreate it on virtio-net
>>> and VF separately again.

How that could work? If you have the VF netdev with all configuration
including IPs and routes and whatever - now you want to do migration
so you add virtio_net and do some weird in-driver bonding with it. But
then, VF disappears and the VF netdev with that and also all
configuration it had.
I don't think this scenario is valid.


>>
>>
>> Yes. This sounds interesting. Looks like you want an existing VM image with
>> VF only configuration to get transparent live migration support by adding
>> virtio_net with BACKUP feature.  We may need another feature bit to switch
>> between these 2 options.
>
>Yes, that's what I was thinking about. I have been building something
>like this before, and would like to get back after merging with your
>patch.