> >> Hmm, right. But do we need the bitmap at all? We can just use > >> > bdrv_is_allocated like bdrv_co_do_readv does. > > If a write occur, we read and backup that cluster immediately (out of > > order). So I am quite sure we need the bitmap. > > This is the same as how copy-on-read happens during image streaming, and it > doesn't use a bitmap.
But a read does not modify the content.
