do_splice
ret = do_splice(in, __off_in, out, __off_out, len, flags);
ssize_t do_splice(struct file *in, loff_t *off_in, struct file *out,
ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);
err = do_splice(peerfd, outfd, size, winfo);
err = do_splice(infd, peerfd, size, winfo);
err = do_splice(infd, peerfd, size, winfo);
err = do_splice(peerfd, outfd, size, winfo);