video: add v4l2-decoder backend

Add new v4l2-decoder backend, that
uses v4l2r [1] for interactions with the
video device in the host. Specialized for
Linux systems.

[1] - https://github.com/Gnurou/v4l2r

Signed-off-by: Albert Esteve <[email protected]>

Author: aesteve-rh

Cargo.lock

@@ -11,7 +11,8 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-default = []
+default = ["v4l2-decoder"]
+v4l2-decoder = ["v4l2r", "nix"]
 
 [dependencies]
 bitflags = "2.3.3"
@@ -29,7 +30,12 @@ virtio-bindings = "0.2.1"
 virtio-queue = "0.9"
 vm-memory = "0.12"
 vmm-sys-util = "0.11"
+nix = { version = "0.27.1", optional = true }
+v4l2r = { git =  "https://github.com/Gnurou/v4l2r", rev = "532c316", optional = true }
 
 [dev-dependencies]
+assert_matches = "1.5"
+rstest = "0.18.2"
+tempfile = "3.8.0"
 virtio-queue = { version = "0.9", features = ["test-utils"] }
 vm-memory = { version = "0.12", features = ["backend-mmap", "backend-atomic"] }

crates/video/Cargo.toml

@@ -103,6 +103,8 @@ impl convert::From<VuVideoError> for io::Error {
 pub(crate) enum BackendType {
     #[default]
     Null,
+    #[cfg(feature = "v4l2-decoder")]
+    V4L2Decoder,
 }
 
 /// Virtio Video Configuration

crates/video/src/vhu_video.rs

@@ -2,7 +2,12 @@
 
 mod null;
 
+#[cfg(feature = "v4l2-decoder")]
+mod v4l2_decoder;
+
 use self::null::NullBackend;
+#[cfg(feature = "v4l2-decoder")]
+use self::v4l2_decoder::V4L2Decoder;
 
 use crate::stream::{ResourcePlane, Stream};
 use crate::vhu_video::{BackendType, Result, VuVideoError};
@@ -78,9 +83,14 @@ pub(crate) fn alloc_video_backend(
     backend: BackendType,
     video_path: &Path,
 ) -> Result<Box<dyn VideoBackend + Sync + Send>> {
-    match backend {
-        BackendType::Null => Ok(Box::new(
-            NullBackend::new(video_path).map_err(|_| VuVideoError::AccessVideoDeviceFile)?,
-        )),
+    macro_rules! build_backend {
+        ($type:ident) => {
+            Box::new($type::new(video_path).map_err(|_| VuVideoError::AccessVideoDeviceFile)?)
+        };
     }
+    Ok(match backend {
+        BackendType::Null => build_backend!(NullBackend),
+        #[cfg(feature = "v4l2-decoder")]
+        BackendType::V4L2Decoder => build_backend!(V4L2Decoder),
+    })
 }