How to open and write to a block driver within a character driver?

I am taksed to develop a Block device driver which will be used within a character device driver so the write to the character driver will be also formatted, converted and duplicated to the block drvice. I am new at this. And I am doing all this within kernel space so I really don't know I can open a block device without using "open" and "write" syscalls. I know there is a generic_make_request call to block driver but it requires the bio vec to be filled out with data and I don't know where to start on that. Any quick solution to this plase? Thanks so much in advance, yx