Re: [Qemu-devel] virtio-gpu doesn't build if you do a linux-headers update from kvm/next

[Laszlo Ersek <lersek@redhat.com>]

On 11/05/15 13:32, Peter Maydell wrote:
> On 5 November 2015 at 12:13, Gerd Hoffmann <kraxel@redhat.com> wrote:
>>> etc, because all the virtio_gpu definitions disappear from
>>> include/standard-headers/linux/virtio_gpu.h.
>>
>> Updates not yet in mainline, they are sitting in drm-next and should
>> land during the merge window (i.e. 4.4-rc1 should have them).
>>
>> I'd suggest to exclude virtio_gpu.h changes when updating linux headers
>> for the time being.
> 
> I would strongly prefer it if we could get to a point where
> we can say "kernel headers must only be updated from this tree"
> and be guaranteed that it always works. This used to be true
> with the tree in question being kvm/next, but it doesn't seem
> to be so now. If it's going to be common that we have header
> changes that don't go via kvm/next, maybe we need to coordinate
> a tree that merges together the abi-guaranteed-stable changes
> from different places before they hit mainline?

I've always frowned upon importing headers from one project to another
project. First, they can have different coding styles. (Case in point.)
Second, not everything that needs to be defined for the original project
is useful to the receiving project, and I find such cruft in the
receiving project very annoying. Third, in some cases it might even
raise licensing questions.

If it is an ABI, it should be specified in text format somewhere, and
then the projects can have their independent type definitions, macros
etc that implement the spec.

Laszlo