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

[Alex Bennée]

Laszlo Ersek <address@hidden> writes:

> On 11/05/15 13:32, Peter Maydell wrote:
>> On 5 November 2015 at 12:13, Gerd Hoffmann <address@hidden> 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.

Surely the kernel uapi includes is that textual format. Once stuff is
accepted into the master kernel tree there is your stable API.

FWIW the few bits I've done that involve syncing headers I basically
carry a [DEV] patch in my QEMU tree until the feature is finally merged
in the kernel and then I do my final re-base against the official tree
state.

-- 
Alex Bennée