docs: add documentation on rutabaga_gfx

The people have demanded it.

BUG=b:291606715
TEST=build docs + view

Change-Id: I22db2fc62d8a09343842d3a7b06dfbd35052e458
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4691162
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Commit-Queue: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Dennis Kempin <denniskempin@google.com>

docs/book/src/SUMMARY.md

@@ -46,6 +46,7 @@ ______________________________________________________________________
   - [Seccomp](./appendix/seccomp.md)
   - [Memory Layout](./appendix/memory_layout.md)
   - [Minijail](./appendix/minijail.md)
+  - [Rutabaga](./appendix/rutabaga_gfx.md)
 
 ______________________________________________________________________
 

docs/book/src/appendix/rutabaga_gfx.md

@@ -0,0 +1,67 @@
+# Rutabaga Virtual Graphics Interface
+
+The Rutabaga Virtual Graphics Interface (VGI) is a cross-platform abstraction for GPU and display
+virtualization. The virtio-gpu
+[context type](https://www.phoronix.com/news/VirtIO-Linux-5.16-Ctx-Type) feature is used to dispatch
+commands between various Rust, C++, and C implementations. The diagram below does not exhaustively
+depict all available context types.
+
+<!-- Image from https://goto.google.com/crosvm-rutabaga-diagram -->
+
+![rutabaga diagram](images/rutabaga_gfx.png)
+
+## Rust API
+
+Although hosted in the crosvm repository, the Rutabaga VGI is designed to be portable across VMM
+implementations. The Rust API is available on [crates.io](https://crates.io/crates/rutabaga_gfx).
+
+## Rutabaga C API
+
+The following documentation shows how to build Rutabaga's C API with gfxstream enabled, which is the
+common use case.
+
+### Build dependencies
+
+```sh
+sudo apt-get install libdrm
+sudo apt-get install libglm-dev
+sudo apt-get install libstb-dev
+```
+
+### Build AEMU base
+
+```sh
+git clone https://android.googlesource.com/platform/hardware/google/aemu
+cmake -DAEMU_COMMON_GEN_PKGCONFIG=ON -DAEMU_COMMON_BUILD_CONFIG=gfxstream
+          -DENABLE_VKCEREAL_TESTS=OFF . ../
+make -j && sudo make install
+```
+
+### Build gfxstream
+
+```sh
+git clone https://android.googlesource.com/platform/hardware/google/gfxstream
+meson -Ddefault_library=static amd64-build/
+ninja -C amd64-build
+sudo ninja -C amd64-build/ install
+```
+
+### Build FFI bindings to Rutabaga
+
+```sh
+cd $(crosvm_dir)/rutabaga_gfx/ffi/
+sudo make install
+```
+
+### Guest-side gfxstream libraries
+
+If your VMM boots to a Linux guest, it's possible to run gfxstream with that.
+
+```sh
+git clone https://android.googlesource.com/device/generic/goldfish-opengl
+cd goldfish-opengl
+meson amd64-build/
+ninja -C amd64-build/ install
+```
+
+Headless Vulkan tests (`deqp-vk`, `vulkaninfo`) should work after that.