Function lf_split

freebsd/kern/kern_lockf.c:1808–1859

* Split an the existing 'lock1', based on the extent of the lock * described by 'lock2'. The existing lock should cover 'lock2' * entirely. * * Any pending locks which have been been unblocked are added to * 'granted' */

 * 'granted'
 */
static void
lf_split(struct lockf *state, struct lockf_entry *lock1,
    struct lockf_entry *lock2, struct lockf_entry_list *granted)
{
	struct lockf_entry *splitlock;

#ifdef LOCKF_DEBUG
	if (lockf_debug & 2) {
		lf_print("lf_split", lock1);
		lf_print("splitting from", lock2);
	}
#endif /* LOCKF_DEBUG */
	/*
	 * Check to see if we don't need to split at all.
	 */
	if (lock1->lf_start == lock2->lf_start) {
		lf_set_start(state, lock1, lock2->lf_end + 1, granted);
		return;
	}
	if (lock1->lf_end == lock2->lf_end) {
		lf_set_end(state, lock1, lock2->lf_start - 1, granted);
		return;
	}
	/*
	 * Make a new lock consisting of the last part of
	 * the encompassing lock.
	 */
	splitlock = lf_alloc_lock(lock1->lf_owner);
	memcpy(splitlock, lock1, sizeof *splitlock);
	splitlock->lf_refs = 1;
	if (splitlock->lf_flags & F_REMOTE)
		vref(splitlock->lf_vnode);

	/*
	 * This cannot cause a deadlock since any edges we would add
	 * to splitlock already exist in lock1. We must be sure to add
	 * necessary dependencies to splitlock before we reduce lock1
	 * otherwise we may accidentally grant a pending lock that
	 * was blocked by the tail end of lock1.
	 */
	splitlock->lf_start = lock2->lf_end + 1;
	LIST_INIT(&splitlock->lf_outedges);
	LIST_INIT(&splitlock->lf_inedges);
	lf_add_incoming(state, splitlock);

	lf_set_end(state, lock1, lock2->lf_start - 1, granted);

	/*
	 * OK, now link it in
	 */
	lf_insert_lock(state, splitlock);
}

struct lockdesc {
	STAILQ_ENTRY(lockdesc) link;