What is clear from the output is that the write() is returning a -1 status. errno could possibly be 0, in which case I set it to ENOSPC, if it is not 0 then it is ENOSPC judging by the error message that is printed "Write error on device ...".

You may want to see more, but here is the basic code that does the write: if ((uint32_t)(stat=write(dev->fd, block->buf, (size_t)wlen)) != wlen) { /* We should check for errno == ENOSPC, BUT many * devices simply report EIO when it is full. * with a little more thought we may be able to check * capacity and distinguish real errors and EOT * conditions. In any case, we probably want to * simulate an End of Medium. */ clrerror_dev(dev, -1);