sound: add AudioBackend trait

crates/sound/src/audio_backends.rs

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: Apache-2.0 or BSD-3-Clause
+
+use crate::{Error, Result, SoundRequest};
+
+pub trait AudioBackend {
+    fn write(&self, req: &SoundRequest) -> Result<()>;
+
+    fn read(&self, req: &mut SoundRequest) -> Result<()>;
+}
+
+pub fn allocate_audio_backend(name: String) -> Result<Box<dyn AudioBackend + Send + Sync>> {
+    match name.as_str() {
+        _ => Err(Error::AudioBackendNotSupported),
+    }
+}

crates/sound/src/lib.rs

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0 or BSD-3-Clause
 
+mod audio_backends;
 mod vhu_sound;
 mod virtio_sound;
 
@@ -10,7 +11,7 @@ use log::{info, warn};
 use thiserror::Error as ThisError;
 use vhost::{vhost_user, vhost_user::Listener};
 use vhost_user_backend::VhostUserDaemon;
-use vm_memory::{GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{GuestMemoryAtomic, GuestMemoryMmap, VolatileSlice};
 
 use crate::vhu_sound::VhostUserSoundBackend;
 
@@ -25,6 +26,10 @@ pub enum Error {
     HandleUnknownEvent,
     #[error("Failed to create a new EventFd")]
     EventFdCreate(IoError),
+    #[error("Request missing data buffer")]
+    SoundReqMissingData,
+    #[error("Audio backend not supported")]
+    AudioBackendNotSupported,
 }
 
 impl std::convert::From<Error> for IoError {
@@ -41,6 +46,8 @@ pub struct SoundConfig {
     socket: String,
     /// use multiple threads to hanlde the virtqueues
     multi_thread: bool,
+    /// audio backend name
+    audio_backend_name: String,
 }
 
 impl SoundConfig {
@@ -50,6 +57,7 @@ impl SoundConfig {
         Self {
             socket,
             multi_thread,
+            audio_backend_name: "null".to_string(),
         }
     }
 
@@ -60,6 +68,19 @@ impl SoundConfig {
     }
 }
 
+pub type SoundBitmap = ();
+
+#[derive(Debug)]
+pub struct SoundRequest<'a> {
+    data_slice: Option<VolatileSlice<'a, SoundBitmap>>,
+}
+
+impl<'a> SoundRequest<'a> {
+    pub fn data_slice(&self) -> Option<&VolatileSlice<'a, SoundBitmap>> {
+        self.data_slice.as_ref()
+    }
+}
+
 /// This is the public API through which an external program starts the
 /// vhost-user-sound backend server.
 pub fn start_backend_server(config: SoundConfig) {
@@ -69,7 +90,7 @@ pub fn start_backend_server(config: SoundConfig) {
     let mut daemon = VhostUserDaemon::new(
         String::from("vhost-user-sound"),
         backend.clone(),
-        GuestMemoryAtomic::new(GuestMemoryMmap::new()),
+        GuestMemoryAtomic::new(GuestMemoryMmap::<SoundBitmap>::new()),
     )
     .unwrap();
 

crates/sound/src/vhu_sound.rs

@@ -1,9 +1,11 @@
 // SPDX-License-Identifier: Apache-2.0 or BSD-3-Clause
 
+use crate::audio_backends::{allocate_audio_backend, AudioBackend};
 use crate::virtio_sound::*;
 use crate::{Error, Result, SoundConfig};
 
-use std::{io::Result as IoResult, sync::RwLock, u16, u32, u64, u8};
+use std::sync::RwLock;
+use std::{io::Result as IoResult, u16, u32, u64, u8};
 use vhost::vhost_user::message::{VhostUserProtocolFeatures, VhostUserVirtioFeatures};
 use vhost_user_backend::{VhostUserBackend, VringRwLock};
 use virtio_bindings::bindings::{
@@ -86,6 +88,7 @@ pub struct VhostUserSoundBackend {
     threads: Vec<RwLock<VhostUserSoundThread>>,
     virtio_cfg: VirtioSoundConfig,
     exit_event: EventFd,
+    _audio_backend: RwLock<Box<dyn AudioBackend + Send + Sync>>,
 }
 
 impl VhostUserSoundBackend {
@@ -108,6 +111,8 @@ impl VhostUserSoundBackend {
             ])?)]
         };
 
+        let audio_backend = allocate_audio_backend(config.audio_backend_name)?;
+
         Ok(Self {
             threads,
             virtio_cfg: VirtioSoundConfig {
@@ -116,6 +121,7 @@ impl VhostUserSoundBackend {
                 chmpas: 0.into(),
             },
             exit_event: EventFd::new(EFD_NONBLOCK).map_err(Error::EventFdCreate)?,
+            _audio_backend: RwLock::new(audio_backend),
         })
     }