quoted

-	rq->__data_len = sdp->sector_size;

quoted

+	rq->__data_len = sdp->sector_size;
+	ret = scsi_init_io(cmd, GFP_ATOMIC);
+	rq->__data_len = nr_bytes;
  	return ret;
  }

Hmm? __data_len is the amount of data written _on the target_.
Do we actually care about it?
And if so, why didn't it break with the original version?
In either case a short description in the patch would be nice.

The drivers care about it, and scsi_init_io uses it as transfer size,
thus we have to set it to the tranfer length before the scsi_init_io
call, and to the full number of bytes to be written after it.

We already do this before the patch, I just moved the first assginment
next to the call to scsi_init_io so that it's more obvious.