rds: refactor zcopy code into rds_message_zcopy_from_user

Move the large block of code predicated on zcopy from
rds_message_copy_from_user into a new function,
rds_message_zcopy_from_user()

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/message.c

@@ -333,14 +333,14 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
 	return rm;
 }
 
-int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from,
-			       bool zcopy)
+int rds_message_zcopy_from_user(struct rds_message *rm, struct iov_iter *from)
 {
-	unsigned long to_copy, nbytes;
 	unsigned long sg_off;
 	struct scatterlist *sg;
 	int ret = 0;
 	int length = iov_iter_count(from);
+	int total_copied = 0;
+	struct sk_buff *skb;
 
 	rm->m_inc.i_hdr.h_len = cpu_to_be32(iov_iter_count(from));
 
@@ -350,54 +350,66 @@ int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from,
 	sg = rm->data.op_sg;
 	sg_off = 0; /* Dear gcc, sg->page will be null from kzalloc. */
 
-	if (zcopy) {
-		int total_copied = 0;
-		struct sk_buff *skb;
-
-		skb = alloc_skb(0, GFP_KERNEL);
-		if (!skb)
-			return -ENOMEM;
-		BUILD_BUG_ON(sizeof(skb->cb) <
-			     max_t(int, sizeof(struct rds_znotifier),
-				   sizeof(struct rds_zcopy_cookies)));
-		rm->data.op_mmp_znotifier = RDS_ZCOPY_SKB(skb);
-		if (mm_account_pinned_pages(&rm->data.op_mmp_znotifier->z_mmp,
-					    length)) {
-			ret = -ENOMEM;
+	skb = alloc_skb(0, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+	BUILD_BUG_ON(sizeof(skb->cb) < max_t(int, sizeof(struct rds_znotifier),
+					     sizeof(struct rds_zcopy_cookies)));
+	rm->data.op_mmp_znotifier = RDS_ZCOPY_SKB(skb);
+	if (mm_account_pinned_pages(&rm->data.op_mmp_znotifier->z_mmp,
+				    length)) {
+		ret = -ENOMEM;
+		goto err;
+	}
+	while (iov_iter_count(from)) {
+		struct page *pages;
+		size_t start;
+		ssize_t copied;
+
+		copied = iov_iter_get_pages(from, &pages, PAGE_SIZE,
+					    1, &start);
+		if (copied < 0) {
+			struct mmpin *mmp;
+			int i;
+
+			for (i = 0; i < rm->data.op_nents; i++)
+				put_page(sg_page(&rm->data.op_sg[i]));
+			mmp = &rm->data.op_mmp_znotifier->z_mmp;
+			mm_unaccount_pinned_pages(mmp);
+			ret = -EFAULT;
 			goto err;
 		}
-		while (iov_iter_count(from)) {
-			struct page *pages;
-			size_t start;
-			ssize_t copied;
-
-			copied = iov_iter_get_pages(from, &pages, PAGE_SIZE,
-						    1, &start);
-			if (copied < 0) {
-				struct mmpin *mmp;
-				int i;
-
-				for (i = 0; i < rm->data.op_nents; i++)
-					put_page(sg_page(&rm->data.op_sg[i]));
-				mmp = &rm->data.op_mmp_znotifier->z_mmp;
-				mm_unaccount_pinned_pages(mmp);
-				ret = -EFAULT;
-				goto err;
-			}
-			total_copied += copied;
-			iov_iter_advance(from, copied);
-			length -= copied;
-			sg_set_page(sg, pages, copied, start);
-			rm->data.op_nents++;
-			sg++;
-		}
-		WARN_ON_ONCE(length != 0);
-		return ret;
+		total_copied += copied;
+		iov_iter_advance(from, copied);
+		length -= copied;
+		sg_set_page(sg, pages, copied, start);
+		rm->data.op_nents++;
+		sg++;
+	}
+	WARN_ON_ONCE(length != 0);
+	return ret;
 err:
-		consume_skb(skb);
-		rm->data.op_mmp_znotifier = NULL;
-		return ret;
-	} /* zcopy */
+	consume_skb(skb);
+	rm->data.op_mmp_znotifier = NULL;
+	return ret;
+}
+
+int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from,
+			       bool zcopy)
+{
+	unsigned long to_copy, nbytes;
+	unsigned long sg_off;
+	struct scatterlist *sg;
+	int ret = 0;
+
+	rm->m_inc.i_hdr.h_len = cpu_to_be32(iov_iter_count(from));
+
+	/* now allocate and copy in the data payload.  */
+	sg = rm->data.op_sg;
+	sg_off = 0; /* Dear gcc, sg->page will be null from kzalloc. */
+
+	if (zcopy)
+		return rds_message_zcopy_from_user(rm, from);
 
 	while (iov_iter_count(from)) {
 		if (!sg_page(sg)) {