On Tue, Feb 19, 2019 at 10:52 PM Gerd Hoffmann <kraxel@redhat.com> wrote:

>   Hi,
>
> > However, dma-buf seems to require either a Linux kernel or a Linux host.
>
> Sure.  They allow passing buffers from one linux driver to another
> without copying the data.
>
> > Dma-bufs aren't also 1:1 with Vulkan host visible memory pointers,
> > or v4l2 codec buffers, or ffmpeg codec buffers, etc.
>
> Some v4l2 drivers have dma-buf support, so you can pass buffers from
> v4l2 to (for example) gpu drivers that way.
>
> > The proposed device would be able to expose memory for direct access in a
> > way that
> > does not couple to dma-buf which is highly desirable for our use case.
> > Using the ping/event messages, even win32 handles and general opaque fds
> > can be passed from host to guest and back.
> >
> > You can think of the proposed device as a 'virtio-dmabuf' that
> > tries to expose shareable memory in a way that disregards implementation
> > details of
> > guest and host kernels.
>
> That would probably look alot like virtio-gpu with only the resource
> handling.  virtio-gpu fundamentally are just buffers.
>
>
This plus new transport makes me wonder if we can have something like a
transport/device pair
where the transport makes it easy to work directly off host memory pci bar,
and the device is virtio-gpu except really just buffers.
We'd really like to go for something like this.

Also virtio-dmabuf would be a pretty bad name.  dma-bufs are not a
> virtio concept, they are a linux concept.  They can be used by linux
> guests, to pass buffers from/to virtio-gpu (note: I'm still busy adding
> driver support for that).  They can be used by linux hosts, to pass
> buffers (with udmabuf help) from qemu to other processes/devices
> (details are still to be hashed out).
>
>
Got it, that sounds pretty interesting.


> Non-linux systems obviously need something else for the job.  The
> guest/host implementation details don't affect the virtio-gpu specs
> though.


While we're talking about this: what is your plan for virtio-gpu
implementations for non-Linux guests/hosts?


>
>
cheers,
>   Gerd
>
>