holdfp_fdp
fp = holdfp_fdp(scred->scr_td->td_proc->p_fd, fd, FREAD|FWRITE);
struct file *holdfp_fdp (struct filedesc *fdp, int fd, int flag);
file = holdfp_fdp(curthread->td_proc->p_fd, args.fd, FREAD | FWRITE);