Running two virtio-sound devices on top of virtio-loopback on AGL Reference Hardware platform (RefHw)
An overview
This guide contains instructions and sources/binaries to manually compile, test and experiment virtio-loopback with two vhost-user sound devices on **AGL reference hardware**. This initial multi-device support was developed to demonstrate the flexibility of virtio-loopback, but it is by no means stable and optimized. The yocto integration of virtio-loopback and vhost-user-sound in AGL is ongoing and is targeting single device support only. Future work idea is to properly support multi-devices in 2024. This work was presented at OSS Japan by Virtual Open Systems (https://ossjapan2023.sched.com/event/1TvYP/virtio-loopback-the-agl-hardware-abstraction-layer-for-non-virtualized-environments-michele-paolino-virtual-open-systems). The code of this demo diverges a bit from the single-device that is targeting upstream in AGL. For instance, it contains makefiles to build two identical virtio-loopback-drivers with different names. For this reason, we placed all the sources/binaries in a temporary public repository available here: https://git.virtualopensystems.com/virtio-loopback/docs/-/tree/multi-sound-guide.
Description of two virtio-sound device running on top of virtio-loopback architecture*
Components
The architecture we want to put in place is composed by the following components:
- [Virtio Loopback Transport](https://git.virtualopensystems.com/virtio-loopback/loopback_driver/-/tree/multi-sound-demo), a Linux module which acts as a transport for the virtio-devices and redirects the virtio messages to the user-space (virtio-loopback-adapter).
- [Virtio Loopback Adapter](https://git.virtualopensystems.com/virtio-loopback/adapter_app/-/tree/multi-sound-demo) is a user-space application which is the intermediate between virtio-loopback-transport and vhost-user-rng device and bridges the communication between them.
- [vhost-device-sound](https://github.com/rust-vmm/vhost-device.git) is the upstream vhost-user-sound device # Instructions for reproducing the VOSYS OSS23 demo
1. Prerequisites
Before start compiling and running the components of the architecture you need:
- **RefHw Linux kernel** dependencies:
+ The following configuration flags need to be enabled: *CONFIG_VIRTIO*, *CONFIG_SND_VIRTIO* -
**RefHw filesystem** dependencies:
+ **alsa-utils** so to use *aplay* command, in order to feed audio stream to a sound device of the system
- **Host system** dependencies + **git** to fetch the sources and patch them before compilation Since RefHw current kernel version is older than v5.13, the virtio-sound driver is not available in the kernel. In that case, patches provided in the virtio_snd_patches subdirectory of the current repo should be applied to the kernel sources. Please find more information about that in the next section (3.1).
2. Build virtio-loopback components
This section focuses on the steps need to be followed in order all the required components of the architecture be compiled. **NOTE**: For simplicity, we will consider to execute all the operations in "$HOME/virtio-loopback-test".
2.1 Backport virtio-sound on kernel v5.10
Patches which backport the virtio-sound driver on kernel v5.10 (used by AGL reference HW) can be found under "virtio_snd_patches/" of the current repo. To apply them to the target kernel (assuming you have sources in the "linux_kernel_source" folder) the following steps are required:
- `cd linux_kernel_source`
- `git am $HOME/virtio-loopback-test/virtio_loopback_guide/virtio_snd_patches/000*`
- `make sound/virtio/virtio_snd.ko`
- For cross-compile please use: `make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- sound/virtio/virtio_snd.ko` >
**NOTE:** A **prebuilt** virtio_snd.ko module can be found under "[prebuilt_binaries](https://git.virtualopensystems.com/virtio-loopback/docs/-/tree/multi-sound-guide/prebuilt_binaries)" directory.
2.2 virtio-loopback driver
The loopback driver is one of two core components of the presented design. It is a kernel module responsible of re-routing virtio messages to the user-space and provides a way to user-space applications to access the vrings. The instructions about how to clone the corresponding repository and build it are the following:
Clone and build loopback driver by executing the following commands:
- `cd $HOME/virtio-loopback-test`
- `git clone git@git.virtualopensystems.com:virtio-loopback/loopback_driver.git`
- `git checkout multi-sound-demo`
- `cd loopback_driver/`
- `./make_loopback.sh` or `./make_loopback.sh 1` for enabling logs
>More in details, the `make` command (used inside the make_loopback.sh script) takes as an argument:
>- 'DEBUG=1' which defines if the driver is going to print logs.
**Note:** Please update the variable *LINUX_DIR* in the "Makefile", pointing to the target linux sources.
> A prebuilt version of loopback modules can be found under "[prebuilt_binaries](https://git.virtualopensystems.com/virtio-loopback/docs/-/tree/multi-sound-guide/prebuilt_binaries)":
> - loopback_driver0.ko, *logs disabled*
> - loopback_driver1.ko, *logs disabled*
> - loopback_driver0_logs.ko
> - loopback_driver1_logs.ko
The kernel side component of the virtio-loopback architecture is now ready to be used. Before proceeding, let's build the user-space component virtio-loopback adapter.
2.3 virtio-loopback adapter
The adapter is the second important component of the presented design and it is responsible of bridging the communication between the vhost-user-device (user-space) and the loopback driver (described in the previous section).
Instructions to clone and build this component are the following:
- `cd $HOME/virtio-loopback-test`
- `git clone git@git.virtualopensystems.com:virtio-loopback/adapter_app.git`
- `git checkout multi-sound-demo`
- `cd adapter_app/`
- `make ARCH=arm64`
More in details, the `make` command takes as an argument:
- 'DEBUG=1' which defines if the adapter is going to print logs.
>**NOTE:** A prebuilt version of adapter's binary can be found under "[prebuilt_binaries](https://git.virtualopensystems.com/virtio-loopback/docs/-/tree/multi-sound-guide/prebuilt_binaries)" directory:
> - adapter, *logs disabled*
> - adapter_logs
Next step is to compile vhost-user-sound device to be able to test the architecture.
2.4 Vhost-user-sound
The third component of the virtio-loopback architecture is the vhost-user-device. Vhost-user-device is the component with whom virtio driver communicates via the path "loopback driver" <-> "adapter". Essentially, it is a user-space driver which virtio tries communicate with.
Instructions to clone and build this modified version are the following:
- `cd $HOME/`
- `git clone https://github.com/rust-vmm/vhost-device.git`
- `cd ./vhost-device/staging/`
- `cargo build --bin vhost-device-sound`
>**NOTE:** A prebuilt version of vhost-device-sound can be found under "[prebuilt_binaries/vhost-device/](https://git.virtualopensystems.com/virtio-loopback/docs/-/tree/multi-sound-guide/prebuilt_binaries/vhost-device)" directory:
> - vhost-device-sound
> - vhost-device-sound.d
>
>Both files needs to be in the same directory
After the above process is completed we should be able to locate vhost-device-sound to the following paths:
- $HOME/vhost-device/staging/target/debug/vhost-device-sound
2.5 Application plays audio stream to a sound system device
In order to perform the multi-virtio-sound demo, we need a simple user-space application that plays a sound stream to a sound device. This application is "aplay" command included in the Pike rootfs with target agl-demo-platform. Also sound samples played during that demo can be found in the subdirectory *sound-samples/*.
3. Run the demonstration
At this point all the components required to start the demo should have been downloaded or built.
System Initialization
This section is an example of how to run two vhost-user-sound on top of the virtio-loopback architecture. It consists of three steps:
- Insert the virtio-sound and virtio-loopback-transport drivers into the kernel
- `insmod` the *virtio_snd.ko* binary
- `insmod $HOME/loopback_driver/virtio-loopback0.ko`
- `insmod $HOME/loopback_driver/virtio-loopback1.ko`
> By using insmod `virtio-loopback*_logs.ko` prebuilt modules, driver's logs can be seen with `dmesg` but this **will** affect performance.
As a result of that process we can see that two new virtio-loopback-driver has been registered in the kernel. This can be verified by running:
```
$ ls /dev/| grep "loopback-"
loopback-X
loopback-Y
```
> X and Y are used to discriminate the two virtio-loopback driver instances.
- Run the vhost-user-devices
- `$HOME/vhost-device/staging/target/debug/vhost-device-sound --socket $HOME/sound.sock0 --backend pipewire`
- `$HOME/vhost-device/staging/target/debug/vhost-device-sound --socket $HOME/sound.sock1 --backend pipewire`
> The "vhost-device-sound" has two arguments "`--socket-path=`" and "`--backend`". The socket argument is the connection between and instance of the vhost-user-device and the virtio-loopback-adapter. Lastly, the backend can be one of the three choices: "null", "alsa", "pipewire". The current demo focuses on "pipewire".
>
> By using `RUST_LOG=trace` you will be able to see vhost-device-sound's logs but this might affect performance.
- Start two instances of virtio-loopback-adapter
- `$HOME/adapter_app/adapter -s /home/root/agl/sound.sock0 -d vhusnd -l X`
- `$HOME/adapter_app/adapter -s /home/root/agl/sound.sock1 -d vhusnd -l Y`
> By using `adapter_logs` prebuilt binary, adapter's logs can be seen in the same terminal but this might affect performance.
After executing those steps, two new virtio-sound devices should appear in the system. We can verify that and find their names by running:
```
$ aplay -l
card 1: SoundCard [VirtIO SoundCard], device 0: virtio-snd [VirtIO PCM 0]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 2: SoundCard_1 [VirtIO SoundCard], device 0: virtio-snd [VirtIO PCM 0]
Subdevices: 1/1
Subdevice #0: subdevice #0
```
Playing audio on Speakers
All the virtio-loopback infrastructure is now in place. Every request to the virtio-sound driver in kernel space, will be forwarded through virtio-loopback driver and adapter components to the vhost-device-sound device running in user space. At last the vhost-device-sound device via "pipewire" and "ALSA" outputs the audio on speakers.
Playing audio to the speakers is done via two simple commands:
- `aplay -D sysdefault:CARD=SoundCard $HOME/sound-pacthes/agl_demo.wav`
+ Playing sound to the speakers via virtio-sound first instance (SoundCard)
- `aplay -D sysdefault:CARD=SoundCard_1 $HOME/sound-pacthes/agl_ic.wav`
+ Playing sound to the speakers via virtio-sound second instance (SoundCard_1)