Function lf_add_edge

freebsd/kern/kern_lockf.c:905–935

* Attempt to record an edge from lock x to lock y. Return EDEADLK if * the new edge would cause a cycle in the owner graph. */

 * the new edge would cause a cycle in the owner graph.
 */
static int
lf_add_edge(struct lockf_entry *x, struct lockf_entry *y)
{
	struct owner_graph *g = &lf_owner_graph;
	struct lockf_edge *e;
	int error;

#ifdef DIAGNOSTIC
	LIST_FOREACH(e, &x->lf_outedges, le_outlink)
		KASSERT(e->le_to != y, ("adding lock edge twice"));
#endif

	/*
	 * Make sure the two owners have entries in the owner graph.
	 */
	lf_alloc_vertex(x);
	lf_alloc_vertex(y);

	error = graph_add_edge(g, x->lf_owner->lo_vertex,
	    y->lf_owner->lo_vertex);
	if (error)
		return (error);

	e = lf_alloc_edge();
	LIST_INSERT_HEAD(&x->lf_outedges, e, le_outlink);
	LIST_INSERT_HEAD(&y->lf_inedges, e, le_inlink);
	e->le_from = x;
	e->le_to = y;

	return (0);
}

/*
 * Remove an edge from the lock graph.