Function dequeue_buffer

rustcv-camera/src/backend/linux/sys.rs:318–326

Dequeue a buffer — retrieve a filled buffer from the driver (VIDIOC_DQBUF). 将缓冲区出队 —— 从驱动取回已写满数据的缓冲区（VIDIOC_DQBUF）。 This call **blocks** until a frame is ready. No `poll()`/`select()` is used, which saves one syscall per frame compared to the `v4l` crate's approach. 此调用会**阻塞**直到帧就绪。不使用 `poll()`/`select()`， 相比 `v4l` crate 的做法每帧节省一次系统调用。 The returned `v4l2_buffer` contains: - `index`: which buffer

(fd: RawFd)

/// - `sequence`：驱动分配的帧序号（用于丢帧检测）
/// - `timestamp`：内核时间戳
pub fn dequeue_buffer(fd: RawFd) -> io::Result<v4l2_buffer> {
    let mut buf: v4l2_buffer = unsafe { std::mem::zeroed() };
    buf.type_ = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    unsafe {
        v4l2_ioctl(fd, VIDIOC_DQBUF, &mut buf as *mut _ as *mut libc::c_void)?;
    }
    Ok(buf)
}

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