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

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Message-Id: <BB2B938F-D2F0-47F8-B651-70EC8A19BC6B@oracle.com>
Date:   Thu, 21 Mar 2019 14:47:50 +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 21 Mar 2019, at 14:37, Michael S. Tsirkin <mst@...hat.com> wrote:
> 
> On Thu, Mar 21, 2019 at 12:07:57PM +0200, Liran Alon wrote:
>>>>>> 2) It brings non-intuitive customer experience. For example, a customer may attempt to analyse connectivity issue by checking the connectivity
>>>>>> on a net-failover slave (e.g. the VF) but will see no connectivity when in-fact checking the connectivity on the net-failover master netdev shows correct connectivity.
>>>>>> 
>>>>>> The set of changes I vision to fix our issues are:
>>>>>> 1) Hide net-failover slaves in a different netns created and managed by the kernel. But that user can enter to it and manage the netdevs there if wishes to do so explicitly.
>>>>>> (E.g. Configure the net-failover VF slave in some special way).
>>>>>> 2) Match the virtio-net and the VF based on a PV attribute instead of MAC. (Similar to as done in NetVSC). E.g. Provide a virtio-net interface to get PCI slot where the matching VF will be hot-plugged by hypervisor.
>>>>>> 3) Have an explicit virtio-net control message to command hypervisor to switch data-path from virtio-net to VF and vice-versa. Instead of relying on intercepting the PCI master enable-bit
>>>>>> as an indicator on when VF is about to be set up. (Similar to as done in NetVSC).
>>>>>> 
>>>>>> Is there any clear issue we see regarding the above suggestion?
>>>>>> 
>>>>>> -Liran
>>>>> 
>>>>> The issue would be this: how do we avoid conflicting with namespaces
>>>>> created by users?
>>>> 
>>>> This is kinda controversial, but maybe separate netns names into 2 groups: hidden and normal.
>>>> To reference a hidden netns, you need to do it explicitly. 
>>>> Hidden and normal netns names can collide as they will be maintained in different namespaces (Yes I’m overloading the term namespace here…).
>>> 
>>> Maybe it's an unnamed namespace. Hidden until userspace gives it a name?
>> 
>> This is also a good idea that will solve the issue. Yes.
>> 
>>> 
>>>> Does this seems reasonable?
>>>> 
>>>> -Liran
>>> 
>>> Reasonable I'd say yes, easy to implement probably no. But maybe I
>>> missed a trick or two.
>> 
>> BTW, from a practical point of view, I think that even until we figure out a solution on how to implement this,
>> it was better to create an kernel auto-generated name (e.g. “kernel_net_failover_slaves")
>> that will break only userspace workloads that by a very rare-chance have a netns that collides with this then
>> the breakage we have today for the various userspace components.
>> 
>> -Liran
> 
> It seems quite easy to supply that as a module parameter. Do we need two
> namespaces though? Won't some userspace still be confused by the two
> slaves sharing the MAC address?

That’s one reasonable option.
Another one is that we will indeed change the mechanism by which we determine a VF should be bonded with a virtio-net device.
i.e. Expose a new virtio-net property that specify the PCI slot of the VF to be bonded with.

The second seems cleaner but I don’t have a strong opinion on this. Both seem reasonable to me and your suggestion is faster to implement from current state of things.

-Liran

> 
> -- 
> MST