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Re: [Qemu-devel] [PATCH V9 01/14] block: move bdrv_snapshot_find() to bl


From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH V9 01/14] block: move bdrv_snapshot_find() to block/snapshot.c
Date: Wed, 13 Mar 2013 19:08:04 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux)

Eric Blake <address@hidden> writes:

> On 03/11/2013 05:23 AM, Wenchao Xia wrote:
>>   This patch adds block/snapshot.c and then moves the function
>> there. It also fixes small code style errors reported by check script.
>> 
>> Signed-off-by: Wenchao Xia <address@hidden>
>> ---
>>  block/Makefile.objs      |    1 +
>>  block/snapshot.c         |   37 +++++++++++++++++++++++++++++++++++++
>>  include/block/snapshot.h |   26 ++++++++++++++++++++++++++
>>  savevm.c                 |   23 +----------------------
>>  4 files changed, 65 insertions(+), 22 deletions(-)
>>  create mode 100644 block/snapshot.c
>>  create mode 100644 include/block/snapshot.h
>
>> +++ b/block/snapshot.c
>> @@ -0,0 +1,37 @@
>> +/*
>> + * Snapshot related functions.
>> + *
>> + * Copyright IBM, Corp. 2013
>
> Technically, since you are moving code from savevm.c, you should also
> preserve the copyright on that moved code:
>
>  * Copyright (c) 2003-2008 Fabrice Bellard
>
>> + *
>> + * Authors:
>> + *  Wenchao Xia   <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU LGPL, version 2 or 
>> later.
>
> Furthermore, the code you are moving was under BSD license, so by moving
> the code, you have changed its license to something more restrictive.
> Personally, I like LGPL better than BSD, but as I'm not the copyright
> holder of the original code, and neither are you, I'm not sure that
> either of us is qualified to make that change.  Therefore, I'm unwilling
> to add my Reviewed-by, even though the code motion itself is correct,
> without a maintainer chiming in on whether your licensing is appropriate
> or needs an adjustment.

Code motion from a single file to a new file is the simplest case.  You
can't go wrong by preserving the license notice exactly then.

Things get a bit messy when you move code to an existing file that
already has a different license notice.  Whether that's even possible
depends on the licenses.

An important special case is adding copyrightable GPL'ed modifications
to a permissively-licensed file.  This need not be just code motion, it
could also happen when you start with a bit of code moved out of a
permissively- licensed file, then add copyrightable code of your own,
which you want protected by the GPL.

For how to do that properly, check out the Software Freedom Law Center's
white paper "Maintaining Permissive-Licensed Files in a GPL-Licensed
Project: Guidelines for Developers"[*] section 2.2 "Adding GPL’d
modifications to permissive-licensed files".

An in-tree example is hw/hd-geometry.c, which I rewrote substantially
after moving it out of block.c,

[*] 
https://www.softwarefreedom.org/resources/2007/gpl-non-gpl-collaboration.html



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