scsi: bsg-lib: handle bidi requests without block layer help

We can just stash away the second request in struct bsg_job instead of
using the block layer req->next_rq field, allowing for the eventual removal
of the latter.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

include/linux/bsg-lib.h

@@ -69,6 +69,10 @@ struct bsg_job {
 	int result;
 	unsigned int reply_payload_rcv_len;
 
+	/* BIDI support */
+	struct request *bidi_rq;
+	struct bio *bidi_bio;
+
 	void *dd_data;		/* Used for driver-specific storage */
 };