netdev - Re: Shepherd request (P83): Multipath TCP: Present Use Cases and an Upstream Future

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Date:   Tue, 22 May 2018 18:46:21 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     "Samudrala, Sridhar" <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: Shepherd request (P83): Multipath TCP: Present Use Cases and an
 Upstream Future

On Tue, May 22, 2018 at 05:36:14PM +0200, Jiri Pirko wrote:
> Tue, May 22, 2018 at 05:28:42PM CEST, sridhar.samudrala@...el.com wrote:
> >
> >On 5/22/2018 2:08 AM, 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.
> >
> >Based on Stephen's feedback on earlier patches, i tried to minimize the changes to
> >netvsc and only commonize the notifier and the main event handler routine.
> >Another complication is that netvsc does part of registration in a delayed workqueue.
> 
> :( This kind of degrades the whole efford of having single solution
> in "failover" module. I think that common parts, as
> netdev_rx_handler_register() and others certainly is should be inside
> the common module. This is not a good time to minimize changes. Let's do
> the thing properly and fix the netvsc mess now.
> 
> 
> >
> >It should be possible to move some of the code from net_failover.c to generic
> >failover.c in future if Stephen is ok with it.
> >
> >
> >> > 
> >> 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.
> >
> >Not sure which code you are referring to.  I only set IFF_FAILOVER_SLAVE
> >in patch 3.
> 
> The existing netvsc driver.

We really can't change netvsc's flags now, even if it's interface is
messy, it's being used in the field. We can add a flag that makes netvsc
behave differently, and if this flag also allows enhanced functionality
userspace will gradually switch.

Anything breaking userspace I fully expect Stephen to nack and
IMO with good reason.

-- 
MST