linux-kernel - Re: [PATCH] add POWER Virtual Management Channel driver

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Date:	Wed, 17 Feb 2016 14:31:41 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Steven Royer <seroyer@...ux.vnet.ibm.com>
Cc:	Jonathan Corbet <corbet@....net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Arnd Bergmann <arnd@...db.de>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Steven Royer <seroyer@...ibm.com>
Subject: Re: [PATCH] add POWER Virtual Management Channel driver

On Wed, Feb 17, 2016 at 03:18:26PM -0600, Steven Royer wrote:
> On 2016-02-16 16:18, Greg Kroah-Hartman wrote:
> >On Tue, Feb 16, 2016 at 02:43:13PM -0600, Steven Royer wrote:
> >>From: Steven Royer <seroyer@...ibm.com>
> >>
> >>The ibmvmc driver is a device driver for the POWER Virtual Management
> >>Channel virtual adapter on the PowerVM platform.  It is used to
> >>communicate with the hypervisor for virtualization management.  It
> >>provides both request/response and asynchronous message support through
> >>the /dev/ibmvmc node.
> >
> >What is the protocol for that device node?
> The protocol is not currently published.  I am pushing on getting it
> published, but that process will take time.  If you have a PowerVM system
> with NovaLink, it would not be hard to reverse engineer it...  If you don't
> have a PowerVM system, then this driver isn't interesting anyway...

You can't just expect us to review this code without at least having a
clue as to how it is supposed to work?

> >Where is the documentation here?  Why does this have to be a character
> >device?  Why can't it fit in with other drivers of this type?
> This is a character device for historical reasons.  The short version is
> that this driver is a clean-room rewrite of an AIX driver which made it a
> character device.  The user space application was ported from AIX to Linux
> and it is convenient to have the AIX and Linux drivers match behavior where
> possible.

Note that we don't let random userspace applications dictate kernel api
decisions, please make the best choice for this interface without being
influenced by AIX.

> >>+/*
> >>+ * IBM Power Systems Virtual Management Channel Support.
> >>+ *
> >>+ * Copyright (c) 2004, 2016 IBM Corp.
> >>+ *   Dave Engebretsen engebret@...ibm.com
> >>+ *   Steven Royer seroyer@...ux.vnet.ibm.com
> >>+ *   Adam Reznechek adreznec@...ux.vnet.ibm.com
> >>+ *
> >>+ * This program is free software; you can redistribute it and/or
> >>+ * modify it under the terms of the GNU General Public License
> >>+ * as published by the Free Software Foundation; either version 2
> >>+ * of the License, or (at your option) any later version.
> >
> >I have to ask, but do you really mean "or any later version"?
> This actually matches closely to other similar PowerVM virtual device
> drivers, like ibmvscsi or ibmveth.

That did not answer the question, picking a license in a cargo-cult
manner is not a wise decision :(