Introduce rq_for_each_segment replacing rq_for_each_bio

Every usage of rq_for_each_bio wraps a usage of
bio_for_each_segment, so these can be combined into
rq_for_each_segment.

We define "struct req_iterator" to hold the 'bio' and 'index' that
are needed for the double iteration.

Signed-off-by: Neil Brown <neilb@suse.de>

Various compile fixes by me...

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/s390/char/tape_3590.c

@@ -623,21 +623,19 @@ tape_3590_bread(struct tape_device *device, struct request *req)
 {
 	struct tape_request *request;
 	struct ccw1 *ccw;
-	int count = 0, start_block, i;
+	int count = 0, start_block;
 	unsigned off;
 	char *dst;
 	struct bio_vec *bv;
-	struct bio *bio;
+	struct req_iterator iter;
 
 	DBF_EVENT(6, "xBREDid:");
 	start_block = req->sector >> TAPEBLOCK_HSEC_S2B;
 	DBF_EVENT(6, "start_block = %i\n", start_block);
 
-	rq_for_each_bio(bio, req) {
-		bio_for_each_segment(bv, bio, i) {
-			count += bv->bv_len >> (TAPEBLOCK_HSEC_S2B + 9);
-		}
-	}
+	rq_for_each_segment(bv, req, iter)
+		count += bv->bv_len >> (TAPEBLOCK_HSEC_S2B + 9);
+
 	request = tape_alloc_request(2 + count + 1, 4);
 	if (IS_ERR(request))
 		return request;
@@ -653,8 +651,7 @@ tape_3590_bread(struct tape_device *device, struct request *req)
 	 */
 	ccw = tape_ccw_cc(ccw, NOP, 0, NULL);
 
-	rq_for_each_bio(bio, req) {
-		bio_for_each_segment(bv, bio, i) {
+	rq_for_each_segment(bv, req, iter) {
 			dst = page_address(bv->bv_page) + bv->bv_offset;
 			for (off = 0; off < bv->bv_len;
 			     off += TAPEBLOCK_HSEC_SIZE) {
@@ -667,7 +664,6 @@ tape_3590_bread(struct tape_device *device, struct request *req)
 			}
 			if (off > bv->bv_len)
 				BUG();
-		}
 	}
 	ccw = tape_ccw_end(ccw, NOP, 0, NULL);
 	DBF_EVENT(6, "xBREDccwg\n");