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

[Alex Bennée]

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?

--
Alex Bennée