Re: [PATCH 5/8] standard-headers: Add virtio_video.h

[Peter Maydell]

On Thu, 9 Dec 2021 at 15:03, Peter Griffin <peter.griffin@linaro.org> wrote:
>
> Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
> ---
>  include/standard-headers/linux/virtio_video.h | 483 ++++++++++++++++++
>  1 file changed, 483 insertions(+)
>  create mode 100644 include/standard-headers/linux/virtio_video.h

As MST notes, content in include/standard-headers/ is from
upstream Linux, and it gets into QEMU by:

 (1) getting it into the Linux kernel tree
 (2) changing QEMU's scripts/update-linux-headers.sh to know that
     it wants this new header file
 (3) running the script to create a patch which updates the headers
     to match a new enough mainline Linux kernel that has the file

This is important because files in standard-headers are used
by QEMU on all host OSes, not just Linux. Things like:

> +#include <linux/virtio_config.h>

or

> +       __le32 version;

won't compile on BSD. The update-linux-headers.sh script takes
care of sanitizing this kind of Linuxism when it copies the
header into the QEMU tree.

The process also ensures that we don't accidentally bring in
support for a kernel feature until its userspace ABI is finalized.

Where a new feature is being worked on on both the kernel and the
QEMU side of things, you can post QEMU RFC patchsets which
temporarily have ad-hoc header file updates (eg created from
a kernel tree that has the not-yet-upstream kernel patches), but
these should be clearly marked as RFCs and we don't take the
QEMU patches until the kernel side is upstream and the QEMU
headers can be cleanly generated from a mainline kernel commit.

thanks
-- PMM