drbd: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()

Use sendmsg() conditionally with MSG_SPLICE_PAGES in _drbd_send_page()
rather than calling sendpage() or _drbd_no_send_page().
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Philipp Reisner <philipp.reisner@linbit.com>
cc: Lars Ellenberg <lars.ellenberg@linbit.com>
cc: "Christoph Böhmwalder" <christoph.boehmwalder@linbit.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: drbd-dev@lists.linbit.com
Link: https://lore.kernel.org/r/20230623225513.2732256-11-dhowells@redhat.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/block/drbd/drbd_main.c

@@ -1540,6 +1540,8 @@ static int _drbd_send_page(struct drbd_peer_device *peer_device, struct page *pa
 		    int offset, size_t size, unsigned msg_flags)
 {
 	struct socket *socket = peer_device->connection->data.socket;
+	struct msghdr msg = { .msg_flags = msg_flags, };
+	struct bio_vec bvec;
 	int len = size;
 	int err = -EIO;
 
@@ -1549,15 +1551,17 @@ static int _drbd_send_page(struct drbd_peer_device *peer_device, struct page *pa
 	 * put_page(); and would cause either a VM_BUG directly, or
 	 * __page_cache_release a page that would actually still be referenced
 	 * by someone, leading to some obscure delayed Oops somewhere else. */
-	if (drbd_disable_sendpage || !sendpage_ok(page))
-		return _drbd_no_send_page(peer_device, page, offset, size, msg_flags);
+	if (!drbd_disable_sendpage && sendpage_ok(page))
+		msg.msg_flags |= MSG_NOSIGNAL | MSG_SPLICE_PAGES;
 
-	msg_flags |= MSG_NOSIGNAL;
 	drbd_update_congested(peer_device->connection);
 	do {
 		int sent;
 
-		sent = socket->ops->sendpage(socket, page, offset, len, msg_flags);
+		bvec_set_page(&bvec, page, offset, len);
+		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
+
+		sent = sock_sendmsg(socket, &msg);
 		if (sent <= 0) {
 			if (sent == -EAGAIN) {
 				if (we_should_drop_the_connection(peer_device->connection, socket))