Re: [RFC PATCH 00/13] gfxstream + rutabaga_gfx: a surprising delight or startling epiphany?

[Gurchetan Singh]

On Fri, Apr 21, 2023 at 9:02 AM Stefan Hajnoczi <stefanha@gmail.com> wrote:
>
> On Thu, 20 Apr 2023 at 21:13, Gurchetan Singh
> <gurchetansingh@chromium.org> wrote:
> >
> > From: Gurchetan Singh <gurchetansingh@google.com>
> >
> > Rationale:
> >
> > - gfxstream [a] is good for the Android Emulator/upstream QEMU
> >   alignment
> > - Wayland passhthrough [b] via the cross-domain context type is good
> >   for Linux on Linux display virtualization
> > - rutabaga_gfx [c] sits on top of gfxstream, cross-domain and even
> >   virglrenderer
> > - This series ports rutabaga_gfx to QEMU
>
> What rutabaga_gfx and gfxstream? Can you explain where they sit in the
> stack and how they build on or complement virtio-gpu and
> virglrenderer?

rutabaga_gfx and gfxstream are both libraries that implement the
virtio-gpu protocol.  There's a document available in the Gitlab issue
to see where they fit in the stack [a].

gfxstream grew out of the Android Emulator's need to virtualize
graphics for app developers.  There's a short history of gfxstream in
patch 10.  It complements virglrenderer in that it's a bit more
cross-platform and targets different use cases -- more detail here
[b].  The ultimate goal is ditch out-of-tree kernel drivers in the
Android Emulator and adopt virtio, and porting gfxstream to QEMU would
speed up that transition.

rutabaga_gfx is a much smaller Rust library that sits on top of
gfxstream and even virglrenderer, but does a few extra things.  It
implements the cross-domain context type, which provides Wayland
passthrough.  This helps virtio-gpu by providing more modern display
virtualization.  For example, Microsoft for WSL2 also uses a similar
technique [c], but I believe it is not virtio-based nor open-source.
With this, we can have the same open-source Wayland passthrough
solution on crosvm, QEMU and even Fuchsia [d].  Also, there might be
an additional small Rust context type for security-sensitive use cases
in the future -- rutabaga_gfx wouldn't compile its gfxstream bindings
(since it's C++ based) in such cases.

Both gfxstream and rutabaga_gfx are a part of the virtio spec [e] now too.

[a] https://gitlab.com/qemu-project/qemu/-/issues/1611
[b] https://lists.gnu.org/archive/html/qemu-devel/2023-03/msg04271.html
[c] https://www.youtube.com/watch?v=EkNBsBx501Q
[d] https://fuchsia-review.googlesource.com/c/fuchsia/+/778764
[e] 
https://github.com/oasis-tcs/virtio-spec/blob/master/device-types/gpu/description.tex#L533

>
> Stefan