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

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Date:   Thu, 21 Mar 2019 15:04:37 +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 14:57, Michael S. Tsirkin <mst@...hat.com> wrote:
> 
> On Thu, Mar 21, 2019 at 02:47:50PM +0200, Liran Alon wrote:
>> 
>> 
>>> 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
> 
> OK. Now what happens if master is moved to another namespace? Do we need
> to move the slaves too?

No. Why would we move the slaves? The whole point is to make most customer ignore the net-failover slaves and remain them “hidden” in their dedicated netns.
We won’t prevent customer from explicitly moving the net-failover slaves out of this netns, but we will not move them out of there automatically.

> 
> Also siwei's patch is then kind of extraneous right?
> Attempts to rename a slave will now fail as it's in a namespace…

I’m not sure actually. Isn't udev/systemd netns-aware?
I would expect it to be able to provide names also to netdevs in netns different than default netns.
If that’s the case, Si-Wei patch to be able to rename a net-failover slave when it is already open is still required. As the race-condition still exists.

-Liran

> 
>>> 
>>> -- 
>>> MST