netdev - Re: [RFC 04/20] RDMA/irdma: Add driver framework definitions

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Date:   Fri, 04 Oct 2019 17:46:15 -0700
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Mustafa Ismail <mustafa.ismail@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Shiraz Saleem <shiraz.saleem@...el.com>
Subject: Re: [RFC 04/20] RDMA/irdma: Add driver framework definitions

On Fri, 2019-10-04 at 23:45 +0000, Jason Gunthorpe wrote:
> On Fri, Oct 04, 2019 at 01:12:22PM -0700, Jeff Kirsher wrote:
> 
> > > > +	if (ldev->version.major != I40E_CLIENT_VERSION_MAJOR ||
> > > > +	    ldev->version.minor != I40E_CLIENT_VERSION_MINOR) {
> > > > +		pr_err("version mismatch:\n");
> > > > +		pr_err("expected major ver %d, caller specified
> > > > major
> > > > ver %d\n",
> > > > +		       I40E_CLIENT_VERSION_MAJOR, ldev-
> > > > >version.major);
> > > > +		pr_err("expected minor ver %d, caller specified
> > > > minor
> > > > ver %d\n",
> > > > +		       I40E_CLIENT_VERSION_MINOR, ldev-
> > > > >version.minor);
> > > > +		return -EINVAL;
> > > > +	}
> > > 
> > > This is can't be in upstream code, we don't support out-of-tree
> > > modules,
> > > everything else will have proper versions.
> > 
> > Who is the "we" in this context?
> 
> Upstream sensibility - if we start doing stuff like this then we will
> end up doing it everwhere.

I see you cut out the part of my response about Linux distributions
disagreeing with this stance.

> 
> > you support out-of-tree drivers, they do exist and this code would
> > ensure that if a "out-of-tree" driver is loaded, the driver will do a
> > sanity check to ensure the RDMA driver will work.
> 
> I don't see how this is any different from any of the other myriad of
> problems out of tree modules face. 
> 
> Someone providing out of tree modules has to provide enough parts of
> their driver so that it only consumes the stable ABI from the distro
> kernel.
> 
> Pretty normal stuff really.

Your right, if the dependency was reversed and the out-of-tree (OOT) driver
was dependent upon the RDMA driver, but in this case it is not.  The LAN
driver does not "need" the RDMA driver to work.  So the RDMA driver should
at least check that the LAN driver loaded has the required version to work.

This line of thinking, "marries" the in-kernel RDMA driver with the in-
kernel LAN driver(s) so the end users and Linux distro's can not choose to
upgrade or use any other driver than what comes with the kernel.  I totally
agree that any out-of-tree (OOT) driver needs to make sure they have all
kernel ABI's figured out for whatever kernel they are being installed on. 
But what is the problem with the in-kernel RDMA driver to do it's own
checks to ensure the driver it is dependent upon meets its minimum
requirements?

Similar checks are done in the Intel LAN driver to ensure the firmware is
of a certain level, which is no different than what is being done here.

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