pn_destroy
pn->pn_destroy = destroy;
pn->pn_destroy = destroy;
pn->pn_destroy = destroy;
if (pn->pn_destroy != NULL)
pn_destroy(pn);
pfs_destroy_t pn_destroy;
KASSERT(pn->pn_destroy != NULL, ("%s(): no callback", __func__));
return ((pn->pn_destroy)(PFS_DESTROY_ARGNAMES));