netdev - Re: [PATCH net-next v11 2/5] netvsc: refactor notifier/event handling code to use the failover framework

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Message-ID: <20180522154501.GL2149@nanopsycho>
Date:   Tue, 22 May 2018 17:45:01 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Sridhar Samudrala <sridhar.samudrala@...el.com>,
        stephen@...workplumber.org, 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, aaron.f.brown@...el.com,
        anjali.singhai@...el.com
Subject: Re: [PATCH net-next v11 2/5] netvsc: refactor notifier/event
 handling code to use the failover framework

Tue, May 22, 2018 at 05:32:30PM CEST, mst@...hat.com wrote:
>On Tue, May 22, 2018 at 05:13:43PM +0200, Jiri Pirko wrote:
>> Tue, May 22, 2018 at 03:39:33PM CEST, mst@...hat.com wrote:
>> >On Tue, May 22, 2018 at 03:26:26PM +0200, Jiri Pirko wrote:
>> >> Tue, May 22, 2018 at 03:17:37PM CEST, mst@...hat.com wrote:
>> >> >On Tue, May 22, 2018 at 03:14:22PM +0200, Jiri Pirko wrote:
>> >> >> Tue, May 22, 2018 at 03:12:40PM CEST, mst@...hat.com wrote:
>> >> >> >On Tue, May 22, 2018 at 11:08:53AM +0200, Jiri Pirko wrote:
>> >> >> >> Tue, May 22, 2018 at 11:06:37AM CEST, jiri@...nulli.us wrote:
>> >> >> >> >Tue, May 22, 2018 at 04:06:18AM CEST, sridhar.samudrala@...el.com wrote:
>> >> >> >> >>Use the registration/notification framework supported by the generic
>> >> >> >> >>failover infrastructure.
>> >> >> >> >>
>> >> >> >> >>Signed-off-by: Sridhar Samudrala <sridhar.samudrala@...el.com>
>> >> >> >> >
>> >> >> >> >In previous patchset versions, the common code did
>> >> >> >> >netdev_rx_handler_register() and netdev_upper_dev_link() etc
>> >> >> >> >(netvsc_vf_join()). Now, this is still done in netvsc. Why?
>> >> >> >> >
>> >> >> >> >This should be part of the common "failover" code.
>> >> >> >> >
>> >> >> >> 
>> >> >> >> Also note that in the current patchset you use IFF_FAILOVER flag for
>> >> >> >> master, yet for the slave you use IFF_SLAVE. That is wrong.
>> >> >> >> IFF_FAILOVER_SLAVE should be used.
>> >> >> >
>> >> >> >Or drop IFF_FAILOVER_SLAVE and set both IFF_FAILOVER and IFF_SLAVE?
>> >> >> 
>> >> >> No. IFF_SLAVE is for bonding.
>> >> >
>> >> >What breaks if we reuse it for failover?
>> >> 
>> >> This is exposed to userspace. IFF_SLAVE is expected for bonding slaves.
>> >> And failover slave is not a bonding slave.
>> >
>> >That does not really answer the question.  I'd claim it's sufficiently
>> >like a bond slave for IFF_SLAVE to make sense.
>> >
>> >In fact you will find that netvsc already sets IFF_SLAVE, and so
>> 
>> netvsc does the whole failover thing in a wrong way. This patchset is
>> trying to fix it.
>
>Maybe, but we don't need gratuitous changes either, especially if they
>break userspace.

What do you mean by the "break"? It was a mistake to reuse IFF_SLAVE at
the first place, lets fix it. If some userspace depends on that flag, it
is broken anyway.


>
>> >does e.g. the eql driver.
>> >
>> >The advantage of using IFF_SLAVE is that userspace knows to skip it.  If
>> 
>> The userspace should know how to skip other types of slaves - team,
>> bridge, ovs, etc.
>> The "master link" should be the one to look at.
>> 
>
>How should existing userspace know which ones to skip and which one is
>the master?  Right now userspace seems to assume whatever does not have
>IFF_SLAVE should be looked at. Are you saying that's not the right thing

Why do you say so? What do you mean by "looked at"? Certainly not.
IFLA_MASTER is the attribute that should be looked at, nothing else.


>to do and userspace should be fixed? What should userspace do in
>your opinion that will be forward compatible with future kernels?
>
>> 
>> >we don't set IFF_SLAVE existing userspace tries to use the lowerdev.
>> 
>> Each master type has a IFF_ master flag and IFF_ slave flag.
>
>Could you give some examples please?

enum netdev_priv_flags {
        IFF_EBRIDGE                     = 1<<1,
        IFF_BRIDGE_PORT                 = 1<<9,
        IFF_OPENVSWITCH                 = 1<<20,
        IFF_OVS_DATAPATH                = 1<<10,
	IFF_L3MDEV_MASTER               = 1<<18,
        IFF_L3MDEV_SLAVE                = 1<<21,
        IFF_TEAM                        = 1<<22,
        IFF_TEAM_PORT                   = 1<<13,
};


>
>> In private
>> flag. I don't see no reason to break this pattern here.
>
>Other masters are setup from userspace, this one is set up automatically
>by kernel. So the bar is higher, we need an interface that existing
>userspace knows about.  We can't just say "oh if userspace set this up
>it should know to skip lowerdevs".
>
>Otherwise multiple interfaces with same mac tend to confuse userspace.

No difference, really.
Regardless who does the setup, and independent userspace deamon should
react accordingly.