Allocates i2o block device specific struct
int i2o_block_prep_req_fn(struct request_queue * q, struct request * req);
q
request queue for the request
req
the request to prepare
Allocate the necessary i2o_block_request struct and connect it to the request. This is needed that we not lose the SG list later on.
Returns BLKPREP_OK on success or BLKPREP_DEFER on failure.