Comment 11 for bug 1619362

As a data-point: using `dd if=image.img of=/dev/device conv=sparse` is not practical, it is very fast (of course) but e.g. uboot.env needs to be written with a lot of \0 in it. It seems that sparse just jump over these (see dd.c:iwrite()) which leads to e.g. a corrupted uboot.env (checksum does no longer match). So we would need something like a `conv=keep-sparse` or something that would only skip writes if the input also is a sparse section. It seems like stock dd does not do that.