Function sys_splice 

pub fn sys_splice(
    locked: &mut Locked<Unlocked>,
    current_task: &CurrentTask,
    fd_in: FdNumber,
    off_in: OffsetPtr,
    fd_out: FdNumber,
    off_out: OffsetPtr,
    len: usize,
    flags: u32,
) -> Result<usize, Errno>