OPEN_RDONLY
err = open_db(hdp, OPEN_RDONLY);
if ((hdp = handle_alloc(root_dir, OPEN_RDONLY)) == NULL) {
again: err = open_db(hdp, OPEN_RDONLY);
assert(flags == OPEN_RDWR || flags == OPEN_RDONLY);
#define IS_RDONLY(f) (((f) & OPEN_FLAGS) == OPEN_RDONLY)
#define HDL_RDONLY(h) (((h)->flags & OPEN_FLAGS) == OPEN_RDONLY)
#define DB_RDONLY(h) ((DB(h)->flags & OPEN_FLAGS) == OPEN_RDONLY)