Re: [Qemu-devel] TCG plugins and the GPL (was: [PATCH v4 00/54] plugins for TCG)

[Daniel P . Berrangé]

On Thu, Sep 12, 2019 at 11:07:07AM +0100, Alex Bennée wrote:
> 
> Peter Maydell <address@hidden> writes:
> 
> > On Thu, 12 Sep 2019 at 10:03, Alex Bennée <address@hidden> wrote:
> >>
> >> Well the first thing will be we are not intending to offer a guaranteed
> >> ABI. While we don't want to be changing it at a whim there shouldn't be
> >> an expectation that the plugin interface will maintain backwards
> >> compatibility (unlike the command line interface ;-). There should be an
> >> expectation that plugins will likely need to be rebuilt against the
> >> current source tree from time to time.
> >
> > Wait, what? From my perspective the whole point of the plugin
> > interface is that it should be stable, in that at least there's
> > a good chance that a plugin you built will work against multiple
> > versions of QEMU, and if it doesn't then it should fail with
> > a reasonable error message telling you to update. I'm not
> > sure we should be landing the plugins infrastructure if we
> > don't have that much stability.
> 
> There is a big fat blurry line between "set in stone" and "not requiring
> you to re-engineer the plugin every QEMU release". I'm saying we should
> reserve the right to extend and change the plugin API as required but
> the expectation would be the plugins will continue to work the same way
> but maybe with tweaks to the API hooks to support additional features.
> 
> It's also a pretty young interface so I would expect some evolution once
> it is released into the field.
> 
> One problem with the anti-license circumvention measures being suggested
> is it will mean having to recompile plugins for any given release. This
> isn't a problem for plugins we write but it does add an extra step for
> out of tree plugins. Maybe being forced to re-compile (but not change
> the source) is a hurdle we are willing to accept?

I can understand & totally support not wishing to break the compilation
of plugins for every release, by having a reasonably stable API.

I think forcing recompile for each release is reasonable protection
to make it less atttractive to create license violating closed source
plugins.

Regards,
Daniel
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