[U-Boot] [PATCH 2/4] Add safe vsnprintf and snprintf library functions

[Graeme Russ]

Hi Sonny,

On Thu, Sep 29, 2011 at 9:26 AM, Sonny Rao <sonnyrao at chromium.org> wrote:
> On Fri, Sep 23, 2011 at 4:56 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
>> Hi Simon,
>>
>> On 24/09/11 03:38, Simon Glass wrote:
>>> From: Sonny Rao <sonnyrao at chromium.org>
>>>
>>> From: Sonny Rao <sonnyrao at chromium.org>
>>>
>>> These functions are useful in U-Boot because they allow a graceful failure
>>> rather than an unpredictable stack overflow when printf() buffers are
>>> exceeded.
>>>
>>> Mostly copied from the Linux kernel. I copied vscnprintf and
>>> scnprintf so we can change printf and vprintf to use the safe
>>> implementation but still return the correct values.
>>
>> Have you checked for license compatibility? U-Boot is GPLv2+ and (most) of
>> Linux is GPLv2 - You may not be legally permitted to do this
>
> According to the FSF site,  GPLv2 is compatible with GPLv3, see:
> http://www.gnu.org/licenses/quick-guide-gplv3.html
>
> So it's fine to distribute them together.

Not so fast:

"GPLv2 is compatible with GPLv3 if the program allows you to choose "any
later version" of the GPL, which is the case for most software released
under this license"

'most', not 'all'

The key phrase is "any later version" - If this is not in the GPLv2
license text for the code your copying, you cannot license the derivative
work under GPLv3 (or GPLv2+)

> In reality though, this code in U-boot was already copied from the
> same file in an older version of the kernel.  The license (GPLv2 only)
> hasn't changed on that file, so U-boot is already distributing what is
> GPLv2 only code alongside GPLv2+ code -- which as I mentioned above is
> fine.

As long as you are not incorporating GPLv2 code into a file licensed under
GPLv2+ and distributing the result as GPLv2+ or GPLv3.

> The code here is derived from a later version of that same file, so I
> don't believe integrating this patch into U-boot actually changes
> anything with respect to licensing of this code.

I think U-Boot will have great difficulty going past GPLv2 due to the
large volume of Linus code already in U-Boot - We would need to either get
the original code relicensed GPLv2+ or rewrite it

And from the COPYING file in the Linux source:

Also note that the only valid version of the GPL as far as the kernel
is concerned is _this_ particular version of the license (ie v2, not
v2.2 or v3.x or whatever), unless explicitly otherwise stated.

and linux/lib/vsprintf.c:

/*
 *  linux/lib/vsprintf.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/* vsprintf.c -- Lars Wirzenius & Linus Torvalds. */
/*
 * Wirzenius wrote this portably, Torvalds fucked it up :-)
 */

/*
 * Fri Jul 13 2001 Crutcher Dunnavant <crutcher+kernel at datastacks.com>
 * - changed to provide snprintf and vsnprintf functions
 * So Feb  1 16:51:32 CET 2004 Juergen Quade <quade at hsnr.de>
 * - scnprintf and vscnprintf
 */

No 'any later version'

Now U-Boot COPYING has:

U-Boot is Free Software.  It is copyrighted by Wolfgang Denk and
many others who contributed code (see the actual source code for
details).  You can redistribute U-Boot and/or modify it under the
terms of version 2 of the GNU General Public License as published by
the Free Software Foundation.  Most of it can also be distributed,
                               -----------------------------------
at your option, under any later version of the GNU General Public
-----------------------------------------------------------------
License -- see individual files for exceptions.
-----------------------------------------------

So U-Boot is also GPLv2, but parts (like Linux) are GPLv2+

My point was there is a long term 'vision' for U-Boot to go GPLv3, and
part of that vision is to reject any future GPLv2 only licensed code
submitted. If we want the vision to be realised, I think we need to
look at how we build new GPLv2+ code in new files rather than tying new
code into GPLv2 only files which may, potentially, lock that code down.
Although as the writer and copyright holder of a modification you may be
free to move it over at a later date anyway - I don't know, and I think
that's in the 'ask a lawyer' territory.

So yes, you are right - In terms of license compliance, we are OK as
U-Boot is currently GPLv2 - In terms of U-Boot going to GPLv3, we are
digging a bigger hole :)

Regards,

Graeme