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

[Kevin Wolf]

Am 13.03.2013 um 19:19 hat Markus Armbruster geschrieben:
> Kevin Wolf <address@hidden> writes:
> 
> > Am 12.03.2013 um 06:01 hat Wenchao Xia geschrieben:
> >>   Oops, Since it belongs to block layer I hope it can be LGPL2. Do you
> >> know how to contact Fabrice Bellard to ask for a change?
> >
> > Fabrice is not the only copyright owner of this file.
> >
> > Just copy the license as it is, changing licenses is always a nasty
> > thing and as I'm not a lawyer I prefer to stay on the safe side. The MIT
> > license works well enough, there's no real reason to change it.
> 
> *Relicensing* a file is indeed "nasty" in the sense that it's a huge
> hassle: you have to track down all copyright holders and get their
> permission.
> 
> But this isn't relicensing.  This is exercising your *right* to
> incorporate permissively-licensed stuff into work covered by a
> compatible, stronger license.  That right was irrevocably granted to you
> by the copyright holders.  You don't have to ask anyone to exercise it.

But you have to do it right. This specific patch would introduce a
copyright violation. It's really not that hard to conform to the terms
of the MIT license, but that doesn't mean that you can ignore it. There
is exactly one requirement and it reads like this:

  The above copyright notice and this permission notice shall be
  included in all copies or substantial portions of the Software.

(I'm still waiting for a patch to blockdev.c, for which you did it
wrong, by the way)

> Of course, the stronger license still has to be compatible with GPLv2,
> so we can accept the result into QEMU.
> 
> If a subsystem has additional requirements on licenses, its maintainers
> will explain them to you.  For what it's worth, substantial parts of the
> block layer are already GPLv2+.

What parts exactly? As long as there are plans for a libqblock and as
long as it doesn't seem completely impossible to have it under LGPL, I
will ask to use either MIT or LGPL for block layer code (this doesn't
apply to qemu-only code that isn't used in the tools - in this sense,
things like blockdev.c are not part of the block layer)

> You don't *have* to switch to a stronger license, of course.  It's your
> choice.  Myself, I prefer to protect any substantial work I do with a
> strong copyleft license such as GPLv2+.

And it's my choice if I accept a patch that does nothing except moving
code and switching to a stronger license. It feels wrong to do this,
even though it may be legal. If you want to change the license for
whatever reason, you should at least add substantial code of your own to
justify this.

Kevin