block: Convert bio_copy_data() to bvec_iter

Our fancy new bvec iterator makes code like this much easier to write.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>

fs/bio.c

@@ -852,58 +852,48 @@ EXPORT_SYMBOL(bio_alloc_pages);
  */
 void bio_copy_data(struct bio *dst, struct bio *src)
 {
-	struct bio_vec *src_bv, *dst_bv;
-	unsigned src_offset, dst_offset, bytes;
+	struct bvec_iter src_iter, dst_iter;
+	struct bio_vec src_bv, dst_bv;
 	void *src_p, *dst_p;
+	unsigned bytes;
 
-	src_bv = __bio_iovec(src);
-	dst_bv = __bio_iovec(dst);
-
-	src_offset = src_bv->bv_offset;
-	dst_offset = dst_bv->bv_offset;
+	src_iter = src->bi_iter;
+	dst_iter = dst->bi_iter;
 
 	while (1) {
-		if (src_offset == src_bv->bv_offset + src_bv->bv_len) {
-			src_bv++;
-			if (src_bv == bio_iovec_idx(src, src->bi_vcnt)) {
+		if (!src_iter.bi_size) {
 			src = src->bi_next;
 			if (!src)
 				break;
 
-				src_bv = __bio_iovec(src);
-			}
-
-			src_offset = src_bv->bv_offset;
+			src_iter = src->bi_iter;
 		}
 
-		if (dst_offset == dst_bv->bv_offset + dst_bv->bv_len) {
-			dst_bv++;
-			if (dst_bv == bio_iovec_idx(dst, dst->bi_vcnt)) {
+		if (!dst_iter.bi_size) {
 			dst = dst->bi_next;
 			if (!dst)
 				break;
 
-				dst_bv = __bio_iovec(dst);
+			dst_iter = dst->bi_iter;
 		}
 
-			dst_offset = dst_bv->bv_offset;
-		}
+		src_bv = bio_iter_iovec(src, src_iter);
+		dst_bv = bio_iter_iovec(dst, dst_iter);
 
-		bytes = min(dst_bv->bv_offset + dst_bv->bv_len - dst_offset,
-			    src_bv->bv_offset + src_bv->bv_len - src_offset);
+		bytes = min(src_bv.bv_len, dst_bv.bv_len);
 
-		src_p = kmap_atomic(src_bv->bv_page);
-		dst_p = kmap_atomic(dst_bv->bv_page);
+		src_p = kmap_atomic(src_bv.bv_page);
+		dst_p = kmap_atomic(dst_bv.bv_page);
 
-		memcpy(dst_p + dst_offset,
-		       src_p + src_offset,
+		memcpy(dst_p + dst_bv.bv_offset,
+		       src_p + src_bv.bv_offset,
 		       bytes);
 
 		kunmap_atomic(dst_p);
 		kunmap_atomic(src_p);
 
-		src_offset += bytes;
-		dst_offset += bytes;
+		bio_advance_iter(src, &src_iter, bytes);
+		bio_advance_iter(dst, &dst_iter, bytes);
 	}
 }
 EXPORT_SYMBOL(bio_copy_data);