buffer: Merge metadata and memory into single Buffer struct

v4l2 users coming from other languages will be used to all the data being
in one place, which is what the C API mandates anyways. Let's stick to the
original data layout for simplicity.

Signed-off-by: Christopher N. Hesse <[email protected]>

examples/glium.rs

@@ -134,12 +134,13 @@ fn main() -> io::Result<()> {
             Stream::<Mmap>::with_buffers(&dev, Type::VideoCapture, buffer_count).unwrap();
 
         loop {
-            let (buf, _) = stream.next().unwrap();
+            let buf = stream.next().unwrap();
             let data = match &format.fourcc.repr {
                 b"RGB3" => buf.to_vec(),
                 b"MJPG" => {
                     // Decode the JPEG frame to RGB
-                    let mut decoder = jpeg::Decoder::new(buf);
+                    let slice: &[u8] = buf;
+                    let mut decoder = jpeg::Decoder::new(slice);
                     decoder.decode().expect("failed to decode JPEG")
                 }
                 _ => panic!("invalid buffer pixelformat"),

examples/stream_capture_mmap.rs

@@ -33,7 +33,7 @@ fn main() -> io::Result<()> {
     let mut megabytes_ps: f64 = 0.0;
     for i in 0..count {
         let t0 = Instant::now();
-        let (buf, meta) = stream.next()?;
+        let buf = stream.next()?;
         let duration_us = t0.elapsed().as_micros();
 
         let cur = buf.len() as f64 / 1_048_576.0 * 1_000_000.0 / duration_us as f64;
@@ -47,9 +47,9 @@ fn main() -> io::Result<()> {
         }
 
         println!("Buffer");
-        println!("  sequence  : {}", meta.sequence);
-        println!("  timestamp : {}", meta.timestamp);
-        println!("  flags     : {}", meta.flags);
+        println!("  sequence  : {}", buf.sequence);
+        println!("  timestamp : {}", buf.timestamp);
+        println!("  flags     : {}", buf.flags);
         println!("  length    : {}", buf.len());
     }
 

examples/stream_capture_userptr.rs

@@ -33,7 +33,7 @@ fn main() -> io::Result<()> {
     let mut megabytes_ps: f64 = 0.0;
     for i in 0..count {
         let t0 = Instant::now();
-        let (buf, meta) = stream.next()?;
+        let buf = stream.next()?;
         let duration_us = t0.elapsed().as_micros();
 
         let cur = buf.len() as f64 / 1_048_576.0 * 1_000_000.0 / duration_us as f64;
@@ -47,9 +47,9 @@ fn main() -> io::Result<()> {
         }
 
         println!("Buffer");
-        println!("  sequence  : {}", meta.sequence);
-        println!("  timestamp : {}", meta.timestamp);
-        println!("  flags     : {}", meta.flags);
+        println!("  sequence  : {}", buf.sequence);
+        println!("  timestamp : {}", buf.timestamp);
+        println!("  flags     : {}", buf.flags);
         println!("  length    : {}", buf.len());
     }
 

examples/stream_forward_mmap.rs

@@ -59,18 +59,18 @@ fn main() -> io::Result<()> {
     let mut megabytes_ps: f64 = 0.0;
     for i in 0..count {
         let t0 = Instant::now();
-        let (buf_in, buf_in_meta) = CaptureStream::next(&mut cap_stream)?;
-        let (buf_out, buf_out_meta) = OutputStream::next(&mut out_stream)?;
+        let buf_in = CaptureStream::next(&mut cap_stream)?;
+        let buf_out = OutputStream::next(&mut out_stream)?;
 
         // Output devices generally cannot know the exact size of the output buffers for
         // compressed formats (e.g. MJPG). They will however allocate a size that is always
         // large enough to hold images of the format in question. We know how big a buffer we need
         // since we control the input buffer - so just enforce that size on the output buffer.
-        let buf_out = &mut buf_out[0..buf_in.len()];
+        let slice_out = &mut buf_out[0..buf_in.len()];
 
-        buf_out.copy_from_slice(buf_in);
-        buf_out_meta.field = 0;
-        buf_out_meta.bytesused = buf_in_meta.bytesused;
+        slice_out.copy_from_slice(buf_in);
+        buf_out.field = 0;
+        buf_out.bytesused = buf_in.bytesused;
         let duration_us = t0.elapsed().as_micros();
 
         let cur = buf_in.len() as f64 / 1_048_576.0 * 1_000_000.0 / duration_us as f64;
@@ -84,12 +84,12 @@ fn main() -> io::Result<()> {
         }
 
         println!("Buffer");
-        println!("  sequence   [in] : {}", buf_in_meta.sequence);
-        println!("  sequence  [out] : {}", buf_out_meta.sequence);
-        println!("  timestamp  [in] : {}", buf_in_meta.timestamp);
-        println!("  timestamp [out] : {}", buf_out_meta.timestamp);
-        println!("  flags      [in] : {}", buf_in_meta.flags);
-        println!("  flags     [out] : {}", buf_out_meta.flags);
+        println!("  sequence   [in] : {}", buf_in.sequence);
+        println!("  sequence  [out] : {}", buf_out.sequence);
+        println!("  timestamp  [in] : {}", buf_in.timestamp);
+        println!("  timestamp [out] : {}", buf_out.timestamp);
+        println!("  flags      [in] : {}", buf_in.flags);
+        println!("  flags     [out] : {}", buf_out.flags);
         println!("  length     [in] : {}", buf_in.len());
         println!("  length    [out] : {}", buf_out.len());
     }

src/buffer.rs

@@ -1,4 +1,7 @@
-use std::fmt;
+use std::{
+    fmt,
+    ops::{Deref, DerefMut},
+};
 
 use crate::timestamp::Timestamp;
 
@@ -98,8 +101,10 @@ impl fmt::Display for Flags {
 }
 
 /// Buffer metadata, mostly used not to convolute the main buffer structs
-#[derive(Copy, Clone, Default)]
-pub struct Metadata {
+#[derive(Debug)]
+pub struct Buffer<T> {
+    /// Backing memory
+    pub memory: T,
     /// Number of bytes occupied by the data in the buffer
     pub bytesused: u32,
     /// Buffer flags
@@ -111,3 +116,30 @@ pub struct Metadata {
     /// Sequence number, counting the frames
     pub sequence: u32,
 }
+
+impl<T> Buffer<T> {
+    pub(crate) fn new(memory: T) -> Self {
+        Buffer {
+            memory,
+            bytesused: 0,
+            flags: Flags::from(0),
+            field: 0,
+            timestamp: Timestamp::default(),
+            sequence: 0,
+        }
+    }
+}
+
+impl<T> Deref for Buffer<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.memory
+    }
+}
+
+impl<T> DerefMut for Buffer<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.memory
+    }
+}

src/io/mod.rs

@@ -11,7 +11,7 @@ use std::{
 
 use v4l2_sys::{v4l2_buffer, v4l2_format, v4l2_requestbuffers};
 
-use crate::buffer::{Metadata, Type};
+use crate::buffer::{Buffer, Type};
 use crate::device::{Device, Handle};
 use crate::io::traits::{CaptureStream, OutputStream, Stream as StreamTrait};
 use crate::memory::{Memory, Mmap, UserPtr};
@@ -23,7 +23,7 @@ use crate::v4l2;
 /// In case of errors during unmapping, we panic because there is memory corruption going on.
 pub(crate) struct Arena<T> {
     handle: Arc<Handle>,
-    pub bufs: Vec<T>,
+    pub bufs: Vec<Buffer<T>>,
     pub buf_mem: Memory,
     pub buf_type: Type,
 }
@@ -119,7 +119,8 @@ impl<'a> Arena<Mmap<'a>> {
 
                 let slice =
                     slice::from_raw_parts_mut::<u8>(ptr as *mut u8, v4l2_buf.length as usize);
-                self.bufs.push(Mmap(slice));
+                let buf = Buffer::new(Mmap(slice));
+                self.bufs.push(buf);
             }
         }
 
@@ -171,8 +172,8 @@ You may want to use this crate with the raw v4l2 FFI bindings instead!\n"
         let count = self.request(count)?;
         for _ in 0..count {
             let size = unsafe { v4l2_fmt.fmt.pix.sizeimage };
-            let buf = vec![0u8; size as usize];
-            self.bufs.push(UserPtr(buf));
+            let buf = Buffer::new(UserPtr(vec![0u8; size as usize]));
+            self.bufs.push(buf);
         }
 
         Ok(count)
@@ -187,7 +188,6 @@ pub struct Stream<T> {
     arena: Arena<T>,
     arena_index: usize,
     buf_type: Type,
-    buf_meta: Vec<Metadata>,
     timeout: Option<i32>,
 
     active: bool,
@@ -220,16 +220,13 @@ impl<'a> Stream<Mmap<'a>> {
 
     pub fn with_buffers(dev: &Device, buf_type: Type, buf_count: u32) -> io::Result<Self> {
         let mut arena = Arena::<Mmap<'a>>::new(dev.handle(), buf_type);
-        let count = arena.allocate(buf_count)?;
-        let mut buf_meta = Vec::new();
-        buf_meta.resize(count as usize, Metadata::default());
+        let _count = arena.allocate(buf_count)?;
 
         Ok(Stream {
             handle: dev.handle(),
             arena,
             arena_index: 0,
             buf_type,
-            buf_meta,
             active: false,
             timeout: None,
         })
@@ -263,16 +260,13 @@ impl Stream<UserPtr> {
 
     pub fn with_buffers(dev: &Device, buf_type: Type, buf_count: u32) -> io::Result<Self> {
         let mut arena = Arena::<UserPtr>::new(dev.handle(), buf_type);
-        let count = arena.allocate(buf_count)?;
-        let mut buf_meta = Vec::new();
-        buf_meta.resize(count as usize, Metadata::default());
+        let _count = arena.allocate(buf_count)?;
 
         Ok(Stream {
             handle: dev.handle(),
             arena,
             arena_index: 0,
             buf_type,
-            buf_meta,
             active: false,
             timeout: None,
         })
@@ -323,7 +317,7 @@ impl<T> Drop for Stream<T> {
 }
 
 impl<T> StreamTrait for Stream<T> {
-    type Item = [u8];
+    type Item = Buffer<T>;
 
     fn start(&mut self) -> io::Result<()> {
         unsafe {
@@ -394,18 +388,17 @@ where
         }
         self.arena_index = v4l2_buf.index as usize;
 
-        self.buf_meta[self.arena_index] = Metadata {
-            bytesused: v4l2_buf.bytesused,
-            flags: v4l2_buf.flags.into(),
-            field: v4l2_buf.field,
-            timestamp: v4l2_buf.timestamp.into(),
-            sequence: v4l2_buf.sequence,
-        };
+        let buf = &mut self.arena.bufs[self.arena_index];
+        buf.bytesused = v4l2_buf.bytesused;
+        buf.flags = v4l2_buf.flags.into();
+        buf.field = v4l2_buf.field;
+        buf.timestamp = v4l2_buf.timestamp.into();
+        buf.sequence = v4l2_buf.sequence;
 
         Ok(self.arena_index)
     }
 
-    fn next(&'a mut self) -> io::Result<(&Self::Item, &Metadata)> {
+    fn next(&'a mut self) -> io::Result<&Self::Item> {
         if !self.active {
             // Enqueue all buffers once on stream start
             for index in 0..self.arena.bufs.len() {
@@ -421,9 +414,7 @@ where
 
         // The index used to access the buffer elements is given to us by v4l2, so we assume it
         // will always be valid.
-        let bytes = &self.arena.bufs[self.arena_index];
-        let meta = &self.buf_meta[self.arena_index];
-        Ok((bytes, meta))
+        Ok(&self.arena.bufs[self.arena_index])
     }
 }
 
@@ -442,8 +433,8 @@ where
             // MetaData.bytesused is initialized to 0. For an output device, when bytesused is
             // set to 0 v4l2 will set it to the size of the plane:
             // https://www.kernel.org/doc/html/v4.15/media/uapi/v4l/buffer.html#struct-v4l2-plane
-            v4l2_buf.bytesused = self.buf_meta[index].bytesused;
-            v4l2_buf.field = self.buf_meta[index].field;
+            v4l2_buf.bytesused = self.arena.bufs[index].bytesused;
+            v4l2_buf.field = self.arena.bufs[index].field;
 
             if self
                 .handle
@@ -476,18 +467,17 @@ where
         }
         self.arena_index = v4l2_buf.index as usize;
 
-        self.buf_meta[self.arena_index] = Metadata {
-            bytesused: v4l2_buf.bytesused,
-            flags: v4l2_buf.flags.into(),
-            field: v4l2_buf.field,
-            timestamp: v4l2_buf.timestamp.into(),
-            sequence: v4l2_buf.sequence,
-        };
+        let buf = &mut self.arena.bufs[self.arena_index];
+        buf.bytesused = v4l2_buf.bytesused;
+        buf.flags = v4l2_buf.flags.into();
+        buf.field = v4l2_buf.field;
+        buf.timestamp = v4l2_buf.timestamp.into();
+        buf.sequence = v4l2_buf.sequence;
 
         Ok(self.arena_index)
     }
 
-    fn next(&'a mut self) -> io::Result<(&mut Self::Item, &mut Metadata)> {
+    fn next(&'a mut self) -> io::Result<&mut Self::Item> {
         let init = !self.active;
         if !self.active {
             self.start()?;
@@ -503,8 +493,6 @@ where
 
         // The index used to access the buffer elements is given to us by v4l2, so we assume it
         // will always be valid.
-        let bytes = &mut self.arena.bufs[self.arena_index];
-        let meta = &mut self.buf_meta[self.arena_index];
-        Ok((bytes, meta))
+        Ok(&mut self.arena.bufs[self.arena_index])
     }
 }

src/io/traits.rs

@@ -1,7 +1,5 @@
 use std::io;
 
-use crate::buffer::Metadata;
-
 /// Streaming I/O
 pub trait Stream {
     type Item: ?Sized;
@@ -22,7 +20,7 @@ pub trait CaptureStream<'a>: Stream {
 
     /// Fetch a new frame by first queueing and then dequeueing.
     /// First time initialization is performed if necessary.
-    fn next(&'a mut self) -> io::Result<(&Self::Item, &Metadata)>;
+    fn next(&'a mut self) -> io::Result<&Self::Item>;
 }
 
 pub trait OutputStream<'a>: Stream {
@@ -34,5 +32,5 @@ pub trait OutputStream<'a>: Stream {
 
     /// Dump a new frame by first queueing and then dequeueing.
     /// First time initialization is performed if necessary.
-    fn next(&'a mut self) -> io::Result<(&mut Self::Item, &mut Metadata)>;
+    fn next(&'a mut self) -> io::Result<&mut Self::Item>;
 }

src/lib.rs

@@ -56,12 +56,12 @@
 //!     Stream::<Mmap>::with_buffers(&mut dev, Type::VideoCapture, 4).expect("Failed to create buffer stream");
 //!
 //! loop {
-//!     let (buf, meta) = stream.next().unwrap();
+//!     let buf = stream.next().unwrap();
 //!     println!(
 //!         "Buffer size: {}, seq: {}, timestamp: {}",
-//!        buf.len(),
-//!        meta.sequence,
-//!        meta.timestamp
+//!        buf.memory.len(),
+//!        buf.sequence,
+//!        buf.timestamp
 //!    );
 //!}
 //!```