|| safe_read (fd, &c, sizeof c) == SAFE_READ_ERROR
|| lseek (fd, (off_t) 0, SEEK_SET) < 0
|| full_write (fd, &c, sizeof c) != sizeof c
|| safe_read (fd, &c, sizeof c) == SAFE_READ_ERROR
|| lseek (fd, (off_t) 0, SEEK_SET) < 0
|| full_write (fd, &c, sizeof c) != sizeof c