OFFTAB_READ_SEEK
assert(ISSET(read_flags, OFFTAB_READ_SEEK) ||
const ssize_t n_read = (ISSET(read_flags, OFFTAB_READ_SEEK)
if (!offtab_maybe_read_window(offtab, blkno, OFFTAB_READ_SEEK))
if (!offtab_maybe_read_window(offtab, blkno, OFFTAB_READ_SEEK))