netdev - Re: [PATCH net] failover: eliminate callback hell

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Date:   Tue, 5 Jun 2018 16:52:22 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, davem@...emloft.net,
        netdev@...r.kernel.org, Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH net] failover: eliminate callback hell

On 6/5/2018 2:52 PM, Stephen Hemminger wrote:
> On Tue, 5 Jun 2018 22:38:43 +0300
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
>
>>> See:
>>>     https://patchwork.ozlabs.org/patch/851711/
>> Let me try to summarize that:
>>
>> 	You wanted to speed up the delayed link up.  You had an idea to
>> 	additionally take link up when userspace renames the interface (standby
>> 	one which is also the failover for netvsc).
>>
>> 	But userspace might not do any renames, in which case there will
>> 	still be the delay, and so this never got applied.
>>
>> 	Is this a good summary?
>>
>> Davem said delay should go away completely as it's not robust, and I
>> think I agree.  So I don't think we should make all failover users use
>> delay. IIUC failover kept a delay option especially for netvsc to
>> minimize the surprise factor. Hopefully we can come up with
>> something more robust and drop that option completely.
> The timeout was the original solution to how to complete setup after
> userspace has had a chance to rename the device. Unfortunately, the whole network
> device initialization (cooperation with udev and userspace) is a a mess because
> there is no well defined specification, and there are multiple ways userspace
> does this in old and new distributions.  The timeout has its own issues
> (how long, handling errors during that window, what if userspace modifies other
> device state); and open to finding a better solution.
>
> My point was that if name change can not be relied on (or used) by netvsc,
> then we can't allow it for net_failover either.

I think the push back was with the usage of the delay, not bringing up the primary/standby
device in the name change event handler.
Can't netvsc use this mechanism instead of depending on the delay?