On Tue, Mar 02, 2021 at 11:54:02AM +0100, Arnd Bergmann wrote:
> On Tue, Mar 2, 2021 at 10:51 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > On Tue, Mar 02, 2021 at 10:42:06AM +0800, Jie Deng wrote:
> > > > > +/*
> > > > > + * Definitions for virtio I2C Adpter
> > > > > + *
> > > > > + * Copyright (c) 2021 Intel Corporation. All rights reserved.
> > > > > + */
> > > > > +
> > > > > +#ifndef _UAPI_LINUX_VIRTIO_I2C_H
> > > > > +#define _UAPI_LINUX_VIRTIO_I2C_H
> > > > Why is this a uapi header? Can't this all be moved into the driver
> > > > itself?
> >
> > Linux VIRTIO drivers provide a uapi header with structs and constants
> > that describe the device interface. This allows other software like
> > QEMU, other operating systems, etc to reuse these headers instead of
> > redefining everything.
> >
> > These files should contain:
> > 1. Device-specific feature bits (VIRTIO_<device>_F_<feature>)
> > 2. VIRTIO Configuration Space layout (struct virtio_<device>_config)
> > 3. Virtqueue request layout (struct virtio_<device>_<req/resp>)
> >
> > For examples, see <linux/virtio_net.h> and <linux/virtio_blk.h>.
> 
> Ok, makes sense. So it's not strictly uapi but just helpful for
> virtio applications to reference these. I suppose it is slightly harder
> when building qemu on other operating systems though, how does
> it get these headers on BSD or Windows?

qemu.git imports Linux headers from time to time and can use them
instead of system headers:

  https://gitlab.com/qemu-project/qemu/-/blob/master/scripts/update-linux-headers.sh

Stefan