Re: [Qemu-devel] [PATCH] Support for loading devices as dynamic libraries

[Stefan Hajnoczi <stefanha@gmail.com>]

On Sat, Aug 25, 2012 at 6:06 PM, Dominik Żeromski <dzeromsk@gmail.com> wrote:
> 2012/8/25 Stefan Hajnoczi <stefanha@gmail.com>
>>
>> On Sat, Aug 25, 2012 at 12:10 PM, Dominik Żeromski <dzeromsk@gmail.com>
>> wrote:
>> > Adding support for loading DSO with -device option.
>> >
>> > Example Makefile for out of tree modules:
>>
>> QEMU does not have a stable ABI for devices.  There is a lot of device
>> model refactoring happening right now for multithreaded MMIO/PIO
>> dispatch and taking advantage of QEMU Object Model.  A stable ABI
>> hinders those kinds of improvements.
>>
>> Send device model patches upstream.  That way you avoid the
>> maintenance overhead of out-of-tree modules and the QEMU community
>> doesn't need to provide a stable ABI.
>>
>
> I think that QEMU is a great tool, not only for server virtualization
> but also for embedded software and hardware development.
>
> I agree that it would be hard to maintain stable ABI, but this is a
> usability feature for device developers, not QEMU developers. I can
> imagine use cases where one team works on a hardware emulator and
> wants to share it with driver team. Driver team doesn't care about how
> QEMU works, how to configure, compile it and then use it. They
> probably use qemu-kvm and libvirt provided by some Linux distribution.
> The distro qemu-kvm does not change much so it wouldn't be a problem
> for emulator team to fix eventual ABI problems. Distributing device as
> dynamic library is simply easier for both teams.

The hardware team can provide a qemu-custom-board binary instead of a
bunch of .so files to the driver team.  That way the whole emulator
can be tested and will never have ABI issues.  Device model plugins
don't improve this scenario.

Stefan