RB_FIRST
lp = RB_FIRST(lwp_rb_tree, &p->p_lwp_tree);
#define FIRST_LWP_IN_PROC(p) RB_FIRST(lwp_rb_tree, &(p)->p_lwp_tree)
while ((io = RB_FIRST(hammer_mod_rb_tree, &hmp->data_root)) != NULL) {
while ((io = RB_FIRST(hammer_mod_rb_tree, &hmp->meta_root)) != NULL) {
while ((io = RB_FIRST(hammer_mod_rb_tree, &hmp->undo_root)) != NULL) {
ip = RB_FIRST(hammer_redo_rb_tree, &hmp->rb_redo_root);