BLOCK_UNDEF
d->page_data[page] = BLOCK_UNDEF;
if (realblock == BLOCK_UNDEF)
d->page_data[page] = BLOCK_UNDEF;
d->page_data[page] = BLOCK_UNDEF;
if (d->page_data[i] != BLOCK_UNDEF)
d->page_data[i] = BLOCK_UNDEF;