at this point):
Replace all '#ifdef DEBUG' with '#ifdef NULLFS_DEBUG' and add NULLFSDEBUG
macro.
Protect nullfs hash table with lockmgr.
Use proper order of operations when freeing mnt_data.
Return correct fsid in the null_getattr().
Add null_open() function to catch MNT_NODEV (obtained from NetBSD).
Add null_rename() to catch cross-fs rename operations (submitted by
Ustimenko Semen <semen@iclub.nsu.ru>)
Remove duplicate $FreeBSD$ tags.
64ac0aa678