It's just a parameter to let the Android OS know that it's running in an emulated environment as opposed to running natively on a physical device.
For example, the GPU stack has to be somehow emulated using a custom OpenGL driver (in this case `mesa3d`). There's software emulation (swiftshader) and host GPU mode (GLES).
For performance reasons when using the host GPU, the GLES commands from the guest have to be serialized and sent over a kernel pipe to the QEMU and to the host OS. The commands are deserialized on the host and executed on the physical host GPU through the Shader Translator library (taken from the Google ANGLE project). The Google's QEMU fork (aka Android Emulator) usually loads this library and then takes care of proper rendering, such that users can see the rendering output of the emulated OS properly inside the emulator window on the host machine. You can do the same for the docker, otherwise you'd have to implement some other trick to share the GPU. `virtio-gpu` is a Linux kernel facility that is meant to replace QEMU pipe in the future.
Yeah not reading anywhere in the docs that it works without qemu. Also the need for kennel modules to be available on the host and passed through makes it less portable than most containers.
Those kernel modules (`ashmem` and `hwbinder`) are standard when building the Linux kernel for Android and they are already part of the upstream Linux kernel tree [1][2]. Because this solution uses containers (which share the same kernel with the host OS), these additional modules are needed.
From the ReDroid kernel modules readme:
>Custom Kernel
>If use custom kernel (5.0+), you can enable binderfs and ashmem configs; So the kernel modules in this repo are not needed any more.
