Merge pull request #129 from Naostage/fix-arena-buffer-usage-v4l

🐛 v4l: fix perf issue introduce by disabled arena buffer

Cargo.toml

@@ -25,6 +25,11 @@ decoding = ["nokhwa-core/mjpeg"]
 input-avfoundation = ["nokhwa-bindings-macos"]
 input-msmf = ["nokhwa-bindings-windows"]
 input-v4l = ["nokhwa-bindings-linux"]
+# Disable arena buffer on v4l
+# This should fix crash on Raspberry Pi that have faulty v4l driver.
+# WARNING: This create a performance regression, half of the frames will be dropped
+# You shouldn't enable this unless you have to.
+input-v4l-no-arena-buffer = ["nokhwa-bindings-linux/no-arena-buffer"]
 input-native = ["input-avfoundation", "input-v4l", "input-msmf"]
 # Re-enable it once soundness has been proven + mozjpeg is updated to 0.9.x
 # input-uvc = ["uvc", "uvc/vendor", "usb_enumeration", "lazy_static"]

nokhwa-bindings-linux/Cargo.toml

@@ -8,6 +8,11 @@ description = "The V4L2 bindings crate for `nokhwa`"
 keywords = ["v4l", "v4l2", "linux", "capture", "webcam"]
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[features]
+# Disable arena buffer of v4l2 for the crate to work on raspberry pi with faulty v4l2 driver
+# https://github.com/l1npengtul/nokhwa/pull/121
+no-arena-buffer = []
+
 [dependencies]
 
 [dependencies.nokhwa-core]

nokhwa-bindings-linux/src/lib.rs

@@ -853,12 +853,17 @@ mod internal {
         }
 
         fn open_stream(&mut self) -> Result<(), NokhwaError> {
+            // Disable mut warning, since mut is only required when not using arena buffers
+            #[allow(unused_mut)]
             let mut stream =
                 match MmapStream::new(&*self.lock_device()?, v4l::buffer::Type::VideoCapture) {
                     Ok(s) => s,
                     Err(why) => return Err(NokhwaError::OpenStreamError(why.to_string())),
                 };
+
             // Explicitly start now, or won't work with the RPi. As a consequence, buffers will only be used as required.
+            // WARNING: This will cause drop of half of the frames
+            #[cfg(feature = "no-arena-buffer")]
             match stream.start() {
                 Ok(s) => s,
                 Err(why) => return Err(NokhwaError::OpenStreamError(why.to_string())),