vhost-device-sound: Add GStreamer audio backend support

Add gstreamer backend.

Add gstreamer-related crates used in the vhost-device-sound
module

This affects only the vhost-device-sound module, and updates the
following dependencies:

- dependency-name: gstreamer
  dependency-version: 0.24.2
- dependency-name: gstreamer-app
  dependency-version: 0.24.2
- dependency-name: gstreamer-audio
  dependency-version: 0.24.2

Signed-off-by: nicholasdezai <nicholasdezai@gmail.com>

vhost-device-sound/CHANGELOG.md

@@ -3,6 +3,7 @@
 
 ### Added
 
+- [[#876]](https://github.com/rust-vmm/vhost-device/pull/876) Add GStreamer audio backend support
 - [[#806]](https://github.com/rust-vmm/vhost-device/pull/806) Add controls field in VirtioSoundConfig
 - [[#746]](https://github.com/rust-vmm/vhost-device/pull/746) Add new sampling rates 12000Hz and 24000Hz
 
@@ -14,6 +15,10 @@
 - [[#808]](https://github.com/rust-vmm/vhost-device/pull/808) pipewire: Fix rand module imports
 - [[#884]](https://github.com/rust-vmm/vhost-device/pull/884) vhost-device-sound/pipewire: fix wrong format
 
+### Limitations
+
+- GStreamer backend: 20-bit PCM formats (VIRTIO_SND_PCM_FMT_S20/U20) are not directly supported by GStreamer and are automatically converted to 24/32-bit formats
+
 ### Deprecated
 
 ## v0.2.0

vhost-device-sound/Cargo.toml

@@ -12,9 +12,10 @@ edition = "2021"
 
 [features]
 xen = ["vm-memory/xen", "vhost/xen", "vhost-user-backend/xen"]
-default = ["alsa-backend", "pw-backend"]
+default = ["alsa-backend", "pw-backend", "gst-backend"]
 alsa-backend = ["dep:alsa"]
 pw-backend = ["pw"]
+gst-backend = ["dep:gst", "dep:gst-app", "dep:gst-audio"]
 
 [dependencies]
 clap = { version = "4.5", features = ["derive"] }
@@ -32,6 +33,9 @@ vmm-sys-util = "0.14"
 [target.'cfg(target_env = "gnu")'.dependencies]
 alsa = { version = "0.10", optional = true }
 pw = { package = "pipewire", version = "0.9.2", optional = true }
+gst = { package = "gstreamer", version = "0.24.2", optional = true, features = ["v1_24"] }
+gst-app = { package = "gstreamer-app", version = "0.24.2", optional = true, features = ["v1_24"] }
+gst-audio = {package = "gstreamer-audio", version = "0.24.2", optional = true, features = ["v1_24"] }
 
 [dev-dependencies]
 rstest = "0.26.1"

vhost-device-sound/README.md

@@ -16,7 +16,7 @@ generated with help2man target/debug/vhost-device-sound |mandoc
             vhost-user Unix domain socket path
 
      --backend <BACKEND>
-            audio backend to be used [possible values: null, pipewire, alsa]
+            audio backend to be used [possible values: null, pipewire, alsa, gstreamer]
 
      -h, --help
             Print help

vhost-device-sound/src/args.rs

@@ -25,4 +25,7 @@ pub enum BackendType {
     Pipewire,
     #[cfg(all(feature = "alsa-backend", target_env = "gnu"))]
     Alsa,
+    #[cfg(all(feature = "gst-backend", target_env = "gnu"))]
+    #[value(name = "gstreamer")]
+    GStreamer,
 }

vhost-device-sound/src/audio_backends.rs

@@ -8,10 +8,15 @@ mod null;
 #[cfg(all(feature = "pw-backend", target_env = "gnu"))]
 mod pipewire;
 
+#[cfg(all(feature = "gst-backend", target_env = "gnu"))]
+mod gstreamer;
+
 use std::sync::{Arc, RwLock};
 
 #[cfg(all(feature = "alsa-backend", target_env = "gnu"))]
 use self::alsa::AlsaBackend;
+#[cfg(all(feature = "gst-backend", target_env = "gnu"))]
+use self::gstreamer::GStreamerBackend;
 use self::null::NullBackend;
 #[cfg(all(feature = "pw-backend", target_env = "gnu"))]
 use self::pipewire::PwBackend;
@@ -61,6 +66,12 @@ pub fn alloc_audio_backend(
         }
         #[cfg(all(feature = "alsa-backend", target_env = "gnu"))]
         BackendType::Alsa => Ok(Box::new(AlsaBackend::new(streams))),
+        #[cfg(all(feature = "gst-backend", target_env = "gnu"))]
+        BackendType::GStreamer => {
+            Ok(Box::new(GStreamerBackend::new(streams).map_err(|err| {
+                crate::Error::UnexpectedAudioBackendError(err.into())
+            })?))
+        }
     }
 }
 

vhost-device-sound/src/audio_backends/gstreamer/test_utils.rs

@@ -0,0 +1,68 @@
+use std::env;
+
+use tempfile::TempDir;
+
+/// A test harness that sets up an isolated environment for GStreamer tests.
+/// Unlike PipeWire, GStreamer is a library and doesn't need a daemon.
+/// We only need to isolate runtime dirs and registry files.
+pub struct GStreamerTestHarness {
+    _runtime_dir: TempDir,
+    old_runtime_dir: Option<String>,
+    old_gst_registry: Option<String>,
+    old_gst_debug: Option<String>,
+}
+
+impl GStreamerTestHarness {
+    /// Create a new isolated GStreamer test environment.
+    pub fn new() -> Self {
+        let tmpdir = tempfile::tempdir().expect("Failed to create temp dir for GStreamer");
+
+        let old_runtime_dir = env::var("XDG_RUNTIME_DIR").ok();
+        let old_gst_registry = env::var("GST_REGISTRY").ok();
+        let old_gst_debug = env::var("GST_DEBUG").ok();
+
+        log::debug!("old_runtime_dir: {:?}", old_runtime_dir);
+        log::debug!("old_gst_registry: {:?}", old_gst_registry);
+        log::debug!("old_gst_debug: {:?}", old_gst_debug);
+
+        env::set_var("XDG_RUNTIME_DIR", tmpdir.path());
+        env::set_var("GST_REGISTRY", tmpdir.path().join("gst-registry.bin"));
+        env::set_var("GST_DEBUG", "ERROR");
+
+        log::debug!(
+            "Started isolated GStreamer test environment at {:?}",
+            tmpdir.path()
+        );
+
+        Self {
+            _runtime_dir: tmpdir,
+            old_runtime_dir,
+            old_gst_registry,
+            old_gst_debug,
+        }
+    }
+}
+
+impl Drop for GStreamerTestHarness {
+    fn drop(&mut self) {
+        if let Some(val) = &self.old_runtime_dir {
+            env::set_var("XDG_RUNTIME_DIR", val);
+        } else {
+            env::remove_var("XDG_RUNTIME_DIR");
+        }
+
+        if let Some(val) = &self.old_gst_registry {
+            env::set_var("GST_REGISTRY", val);
+        } else {
+            env::remove_var("GST_REGISTRY");
+        }
+
+        if let Some(val) = &self.old_gst_debug {
+            env::set_var("GST_DEBUG", val);
+        } else {
+            env::remove_var("GST_DEBUG");
+        }
+
+        log::debug!("Isolated GStreamer environment cleaned up");
+    }
+}

vhost-device-sound/src/main.rs

@@ -55,6 +55,10 @@ mod tests {
         all(feature = "alsa-backend", target_env = "gnu"),
         case::alsa("alsa", BackendType::Alsa)
     )]
+    #[cfg_attr(
+        all(feature = "gst-backend", target_env = "gnu"),
+        case::gstreamer("gstreamer", BackendType::GStreamer)
+    )]
     fn test_cli_backend_arg(#[case] backend_name: &str, #[case] backend: BackendType) {
         let args: SoundArgs = Parser::parse_from([
             "",

vhost-device-sound/src/stream.rs

@@ -29,6 +29,12 @@ pub enum Error {
     DescriptorWriteFailed,
     #[error("Could not disconnect stream")]
     CouldNotDisconnectStream,
+    #[cfg(feature = "gst-backend")]
+    #[error("Could not start stream")]
+    CouldNotStartStream,
+    #[cfg(feature = "gst-backend")]
+    #[error("Could not stop stream")]
+    CouldNotStopStream,
 }
 
 type Result<T> = std::result::Result<T, Error>;
@@ -323,7 +329,8 @@ impl Request {
     }
 
     #[inline]
-    /// Returns the length of the sound data [`virtio_queue::desc::RawDescriptor`].
+    /// Returns the length of the sound data
+    /// [`virtio_queue::desc::RawDescriptor`].
     pub const fn len(&self) -> usize {
         self.len
     }