netdev - Re: [summary] virtio network device failover writeup

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Message-Id: <79F5D7C0-BBAA-4F78-9039-27A444970002@oracle.com>
Date:   Wed, 20 Mar 2019 01:25:58 +0200
From:   Liran Alon <liran.alon@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jakub Kicinski <kubakici@...pl>, Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        boris.ostrovsky@...cle.com, vijay.balakrishna@...cle.com,
        jfreimann@...hat.com, ogerlitz@...lanox.com, vuhuong@...lanox.com
Subject: Re: [summary] virtio network device failover writeup



> On 19 Mar 2019, at 23:19, Michael S. Tsirkin <mst@...hat.com> wrote:
> 
> On Tue, Mar 19, 2019 at 08:46:47AM -0700, Stephen Hemminger wrote:
>> On Tue, 19 Mar 2019 14:38:06 +0200
>> Liran Alon <liran.alon@...cle.com> wrote:
>> 
>>> b.3) cloud-init: If configured to perform network-configuration, it attempts to configure all available netdevs. It should avoid however doing so on net-failover slaves.
>>> (Microsoft has handled this by adding a mechanism in cloud-init to blacklist a netdev from being configured in case it is owned by a specific PCI driver. Specifically, they blacklist Mellanox VF driver. However, this technique doesn’t work for the net-failover mechanism because both the net-failover netdev and the virtio-net netdev are owned by the virtio-net PCI driver).
>> 
>> Cloud-init should really just ignore all devices that have a master device.
>> That would have been more general, and safer for other use cases.
> 
> Given lots of userspace doesn't do this, I wonder whether it would be
> safer to just somehow pretend to userspace that the slave links are
> down? And add a special attribute for the actual link state.

I think this may be problematic as it would also break legit use case of userspace attempt to set various config on VF slave.
In general, lying to userspace usually leads to problems. If we reach to a scenario where we try to avoid userspace issues generically and not
on a userspace component basis, I believe the right path should be to hide the net-failover slaves such that explicit action is required
to actually manipulate them (As described in blog-post). E.g. Automatically move net-failover slaves by kernel to a different netns.

-Liran

> 
> -- 
> MST