Function lf_add_outgoing

freebsd/kern/kern_lockf.c:985–1047

* Walk the list of locks for the file and create an out-going edge * from lock to each blocking lock. */

 * from lock to each blocking lock.
 */
static int
lf_add_outgoing(struct lockf *state, struct lockf_entry *lock)
{
	struct lockf_entry *overlap;
	int error;

	LIST_FOREACH(overlap, &state->ls_active, lf_link) {
		/*
		 * We may assume that the active list is sorted by
		 * lf_start.
		 */
		if (overlap->lf_start > lock->lf_end)
			break;
		if (!lf_blocks(lock, overlap))
			continue;

		/*
		 * We've found a blocking lock. Add the corresponding
		 * edge to the graphs and see if it would cause a
		 * deadlock.
		 */
		error = lf_add_edge(lock, overlap);

		/*
		 * The only error that lf_add_edge returns is EDEADLK.
		 * Remove any edges we added and return the error.
		 */
		if (error) {
			lf_remove_outgoing(lock);
			return (error);
		}
	}

	/*
	 * We also need to add edges to sleeping locks that block
	 * us. This ensures that lf_wakeup_lock cannot grant two
	 * mutually blocking locks simultaneously and also enforces a
	 * 'first come, first served' fairness model. Note that this
	 * only happens if we are blocked by at least one active lock
	 * due to the call to lf_getblock in lf_setlock below.
	 */
	LIST_FOREACH(overlap, &state->ls_pending, lf_link) {
		if (!lf_blocks(lock, overlap))
			continue;
		/*
		 * We've found a blocking lock. Add the corresponding
		 * edge to the graphs and see if it would cause a
		 * deadlock.
		 */
		error = lf_add_edge(lock, overlap);

		/*
		 * The only error that lf_add_edge returns is EDEADLK.
		 * Remove any edges we added and return the error.
		 */
		if (error) {
			lf_remove_outgoing(lock);
			return (error);