Function request_buffers

rustcv-camera/src/backend/linux/sys.rs:259–268

Request mmap buffers from the kernel (VIDIOC_REQBUFS). 向内核申请 mmap 缓冲区（VIDIOC_REQBUFS）。 The kernel may allocate fewer buffers than requested. Check `reqbufs.count` for the actual number. 内核可能分配比请求更少的缓冲区。检查 `reqbufs.count` 获取实际数量。

(fd: RawFd, count: u32)

/// Check `reqbufs.count` for the actual number.
/// 内核可能分配比请求更少的缓冲区。检查 `reqbufs.count` 获取实际数量。
pub fn request_buffers(fd: RawFd, count: u32) -> io::Result<v4l2_requestbuffers> {
    let mut req: v4l2_requestbuffers = unsafe { std::mem::zeroed() };
    req.count = count;
    req.type_ = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;
    unsafe {
        v4l2_ioctl(fd, VIDIOC_REQBUFS, &mut req as *mut _ as *mut libc::c_void)?;
    }
    Ok(req)
}

/// Query a single buffer's offset and length (VIDIOC_QUERYBUF).
/// 查询单个缓冲区的偏移量和大小（VIDIOC_QUERYBUF）。