netdev - Re: [net-next] i40iw/i40e: Remove link dependency on i40e

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Message-ID: <20180522213334.GE7502@mellanox.com>
Date:   Tue, 22 May 2018 15:33:34 -0600
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     davem@...emloft.net, dledford@...hat.com,
        Sindhu Devale <sindhu.devale@...el.com>,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com,
        Shiraz Saleem <shiraz.saleem@...el.com>
Subject: Re: [net-next] i40iw/i40e: Remove link dependency on i40e

On Tue, May 22, 2018 at 02:04:06PM -0700, Jeff Kirsher wrote:
> On Tue, 2018-05-22 at 14:56 -0600, Jason Gunthorpe wrote:
> > On Tue, May 22, 2018 at 01:38:31PM -0700, Jeff Kirsher wrote:
> > > From: Sindhu Devale <sindhu.devale@...el.com>
> > > 
> > > Currently i40iw is dependent on i40e symbols
> > > i40e_register_client and i40e_unregister_client due to
> > > which i40iw cannot be loaded without i40e being loaded.
> > > 
> > > This patch allows RDMA driver to build and load without
> > > linking to LAN driver and without LAN driver being loaded
> > > first. Once the LAN driver is loaded, the RDMA driver
> > > is notified through the netdevice notifiers to register
> > > as client to the LAN driver. Add function pointers to IDC
> > > register/unregister in the private VSI structure. This
> > > allows a RDMA driver to build without linking to i40e.
> > 
> > Why would you want to do this? The rdma driver is non-functional
> > without the ethernet driver, so why on earth would we want to defeat
> > the module dependency mechanism?
> 
> This change is driven by the OSV's like Red Hat, where customer's were
> updating the i40e driver, which in turn broke i40iw.

So that isn't a reason to put something into the main line kernel, and
I'm deeply skeptical this change is even sane.

It has been a while since I've looked at RH's kernel, but AFAIK,
breakage should only happen if the ABIs around
i40e_unregister_client/etc change..

So if the i40e module updates breaks the ABI, then stuffing that same
broken ABI through a function pointer is *totally* wrong.

Looks like a NAK for the RDMA side.

Jason