memory: Create proper types for v4l2 buffer memory

Signed-off-by: Christopher N. Hesse <raymanfx@gmail.com>

src/io/mmap/arena.rs

@@ -4,7 +4,7 @@ use v4l2_sys::{v4l2_buffer, v4l2_requestbuffers};
 
 use crate::buffer;
 use crate::device::Handle;
-use crate::memory::Memory;
+use crate::memory::{Memory, Mmap};
 use crate::v4l2;
 
 /// Manage mapped buffers
@@ -13,7 +13,7 @@ use crate::v4l2;
 /// In case of errors during unmapping, we panic because there is memory corruption going on.
 pub struct Arena<'a> {
     handle: Arc<Handle>,
-    pub bufs: Vec<&'a mut [u8]>,
+    pub bufs: Vec<Mmap<'a>>,
     pub buf_type: buffer::Type,
 }
 
@@ -87,20 +87,14 @@ impl<'a> Arena<'a> {
 
                 let slice =
                     slice::from_raw_parts_mut::<u8>(ptr as *mut u8, v4l2_buf.length as usize);
-                self.bufs.push(slice);
+                self.bufs.push(Mmap(slice));
             }
         }
 
         Ok(v4l2_reqbufs.count)
     }
 
     pub fn release(&mut self) -> io::Result<()> {
-        for buf in &self.bufs {
-            unsafe {
-                v4l2::munmap(buf.as_ptr() as *mut core::ffi::c_void, buf.len())?;
-            }
-        }
-
         // free all buffers by requesting 0
         let mut v4l2_reqbufs = v4l2_requestbuffers {
             count: 0,

src/io/userptr/arena.rs

@@ -4,15 +4,15 @@ use v4l2_sys::{v4l2_format, v4l2_requestbuffers};
 
 use crate::buffer;
 use crate::device::Handle;
-use crate::memory::Memory;
+use crate::memory::{Memory, UserPtr};
 use crate::v4l2;
 
 /// Manage user allocated buffers
 ///
 /// All buffers are released in the Drop impl.
 pub struct Arena {
     handle: Arc<Handle>,
-    pub bufs: Vec<Vec<u8>>,
+    pub bufs: Vec<UserPtr>,
     pub buf_type: buffer::Type,
 }
 
@@ -76,12 +76,10 @@ impl Arena {
         }
 
         // allocate the new user buffers
-        self.bufs.resize(v4l2_reqbufs.count as usize, Vec::new());
-        for i in 0..v4l2_reqbufs.count {
-            let buf = &mut self.bufs[i as usize];
-            unsafe {
-                buf.resize(v4l2_fmt.fmt.pix.sizeimage as usize, 0);
-            }
+        for _ in 0..v4l2_reqbufs.count {
+            let size = unsafe { v4l2_fmt.fmt.pix.sizeimage };
+            let buf = vec![0u8; size as usize];
+            self.bufs.push(UserPtr(buf));
         }
 
         Ok(v4l2_reqbufs.count)

src/memory.rs

@@ -1,4 +1,9 @@
-use std::fmt;
+use std::{
+    fmt,
+    ops::{Deref, DerefMut},
+};
+
+use crate::v4l2;
 
 /// Memory used for buffer exchange
 #[allow(clippy::unreadable_literal)]
@@ -21,3 +26,57 @@ impl fmt::Display for Memory {
         }
     }
 }
+
+/// Memory-mapped region
+///
+/// The backing memory is usually located somewhere on the camera hardware itself. It is mapped
+/// into RAM so data can be copied. In case of capture devices, the (virtual) memory can be read.
+/// In case of output devices, it can be written.
+///
+/// The destructor automatically unmaps the memory.
+#[derive(Debug)]
+pub struct Mmap<'a>(pub(crate) &'a mut [u8]);
+
+impl Drop for Mmap<'_> {
+    fn drop(&mut self) {
+        unsafe {
+            // ignore errors
+            let _ = v4l2::munmap(self.0.as_mut_ptr() as *mut core::ffi::c_void, self.0.len());
+        }
+    }
+}
+
+impl Deref for Mmap<'_> {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+
+impl DerefMut for Mmap<'_> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.0
+    }
+}
+
+/// Userspace memory
+///
+/// This memory type can be used to directly make the camera hardware write its data into the
+/// user-provided buffer (which lives in userspace).
+#[derive(Clone, Debug)]
+pub struct UserPtr(pub(crate) Vec<u8>);
+
+impl Deref for UserPtr {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for UserPtr {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}