Function tty_wait_background

freebsd/kern/tty.c:423–501

}

int
tty_wait_background(struct tty *tp, struct thread *td, int sig)
{
	struct proc *p;
	struct pgrp *pg;
	ksiginfo_t ksi;
	int error;

	MPASS(sig == SIGTTIN || sig == SIGTTOU);
	tty_assert_locked(tp);

	p = td->td_proc;
	for (;;) {
		pg = p->p_pgrp;
		PGRP_LOCK(pg);
		PROC_LOCK(p);

		/*
		 * pg may no longer be our process group.
		 * Re-check after locking.
		 */
		if (p->p_pgrp != pg) {
			PROC_UNLOCK(p);
			PGRP_UNLOCK(pg);
			continue;
		}

		/*
		 * The process should only sleep, when:
		 * - This terminal is the controlling terminal
		 * - Its process group is not the foreground process
		 *   group
		 * - The parent process isn't waiting for the child to
		 *   exit
		 * - the signal to send to the process isn't masked
		 */
		if (!tty_is_ctty(tp, p) || p->p_pgrp == tp->t_pgrp) {
			/* Allow the action to happen. */
			PROC_UNLOCK(p);
			PGRP_UNLOCK(pg);
			return (0);
		}

		if (SIGISMEMBER(p->p_sigacts->ps_sigignore, sig) ||
		    SIGISMEMBER(td->td_sigmask, sig)) {
			/* Only allow them in write()/ioctl(). */
			PROC_UNLOCK(p);
			PGRP_UNLOCK(pg);
			return (sig == SIGTTOU ? 0 : EIO);
		}

		if ((p->p_flag & P_PPWAIT) != 0 ||
		    (pg->pg_flags & PGRP_ORPHANED) != 0) {
			/* Don't allow the action to happen. */
			PROC_UNLOCK(p);
			PGRP_UNLOCK(pg);
			return (EIO);
		}