netdev - Re: [PATCH net-next v10 2/4] net: Introduce generic failover module

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Message-ID: <d4b8dcae-3d21-3b8b-5881-1fc15617d18a@intel.com>
Date:   Mon, 7 May 2018 17:11:21 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     mst@...hat.com, davem@...emloft.net, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl, jasowang@...hat.com,
        loseweigh@...il.com, jiri@...nulli.us, aaron.f.brown@...el.com
Subject: Re: [PATCH net-next v10 2/4] net: Introduce generic failover module

On 5/7/2018 4:59 PM, Stephen Hemminger wrote:
> On Mon,  7 May 2018 15:10:44 -0700
> Sridhar Samudrala <sridhar.samudrala@...el.com> wrote:
>
>> +	if (netif_running(failover_dev)) {
>> +		err = dev_open(slave_dev);
>> +		if (err && (err != -EBUSY)) {
>> +			netdev_err(failover_dev, "Opening slave %s failed err:%d\n",
>> +				   slave_dev->name, err);
>> +			goto err_dev_open;
>> +		}
>> +	}
>> +
>> +	netif_addr_lock_bh(failover_dev);
>> +	dev_uc_sync_multiple(slave_dev, failover_dev);
>> +	dev_uc_sync_multiple(slave_dev, failover_dev);
>> +	netif_addr_unlock_bh(failover_dev);
>> +
> The order of these is backwards, you want to sync addresses before bringing up.
> Also, doing it this way does not allow udev/systemd the chance to rename VF devices.

During my testing, i noticed that dev_open() may fail with EBUSY in certain scenarios,
If so, the opening of the slave is handled after the rename via the NETDEV_CHANGENAME
event handler.

>
> The complexity of this whole failover mechanism does not make life easier,
> more reliable, or safer for netvsc. I though that was the whole reason for having
> common code.

netvsc doesn't go through this code.

	if (nfo_ops && nfo_ops->slave_register)
                 return nfo_ops->slave_register(slave_dev, failover_dev);

So there is no change in event handling for netvsc 2-netdev model.