chore: vendor trimmed v4l2r capture crate

libs/v4l2r/src/ioctl/mmap.rs

@@ -0,0 +1,117 @@
+use core::num::NonZeroUsize;
+use std::{
+    cmp::{max, min},
+    ops::Deref,
+    ptr::NonNull,
+    slice,
+};
+use std::{ops::DerefMut, os::unix::io::AsFd};
+
+use log::error;
+use nix::{errno::Errno, libc::off_t, sys::mman};
+use thiserror::Error;
+
+pub struct PlaneMapping {
+    // A mapping remains valid until we munmap it, that is, until the
+    // PlaneMapping object is deleted. Hence the static lifetime.
+    pub data: &'static mut [u8],
+
+    start: usize,
+    end: usize,
+}
+
+impl PlaneMapping {
+    pub fn size(&self) -> usize {
+        self.end - self.start
+    }
+
+    pub fn restrict(mut self, start: usize, end: usize) -> Self {
+        self.start = max(self.start, start);
+        self.end = min(self.end, end);
+
+        self
+    }
+}
+
+impl AsRef<[u8]> for PlaneMapping {
+    fn as_ref(&self) -> &[u8] {
+        &self.data[self.start..self.end]
+    }
+}
+
+impl AsMut<[u8]> for PlaneMapping {
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.data[self.start..self.end]
+    }
+}
+
+impl Deref for PlaneMapping {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        &self.data[self.start..self.end]
+    }
+}
+
+impl DerefMut for PlaneMapping {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.data[self.start..self.end]
+    }
+}
+
+impl Drop for PlaneMapping {
+    fn drop(&mut self) {
+        // Safe because the pointer and length were constructed in mmap() and
+        // are always valid.
+        unsafe {
+            mman::munmap(
+                NonNull::new_unchecked(self.data.as_mut_ptr().cast()),
+                self.data.len(),
+            )
+        }
+        .unwrap_or_else(|e| {
+            error!("Error while unmapping plane: {}", e);
+        });
+    }
+}
+
+#[derive(Debug, Error)]
+pub enum MmapError {
+    #[error("provided length was 0")]
+    ZeroLength,
+    #[error("ioctl error: {0}")]
+    IoctlError(#[from] Errno),
+}
+
+impl From<MmapError> for Errno {
+    fn from(err: MmapError) -> Self {
+        match err {
+            MmapError::ZeroLength => Errno::EINVAL,
+            MmapError::IoctlError(e) => e,
+        }
+    }
+}
+
+// TODO should be unsafe because the mapping can be used after a buffer is queued?
+// Or not, since this cannot cause a crash...
+pub fn mmap(fd: &impl AsFd, mem_offset: u32, length: u32) -> Result<PlaneMapping, MmapError> {
+    let non_zero_length = NonZeroUsize::new(length as usize).ok_or(MmapError::ZeroLength)?;
+    let data = unsafe {
+        mman::mmap(
+            None,
+            non_zero_length,
+            mman::ProtFlags::PROT_READ | mman::ProtFlags::PROT_WRITE,
+            mman::MapFlags::MAP_SHARED,
+            fd,
+            mem_offset as off_t,
+        )
+    }?;
+
+    Ok(PlaneMapping {
+        // Safe because we know the pointer is valid and has enough data mapped
+        // to cover the length.
+        data: unsafe { slice::from_raw_parts_mut(data.as_ptr().cast(), length as usize) },
+        start: 0,
+        end: length as usize,
+    })
+}