drbd: debugfs: add per connection oldest requests

Information of former /sys/block/drbdX/drbd/oldest_requests
is already with higher detail in these files:
 debugfs/drbd/resource/$name/in_flight_summary,
 debugfs/drbd/resource/$name/volumes/$vnr/oldest_requests

This patch adds
 debugfs/drbd/resource/$name/connections/peer/oldest_requests
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_debugfs.c

@@ -670,6 +670,13 @@ void drbd_debugfs_connection_add(struct drbd_connection *connection)
 	if (IS_ERR_OR_NULL(dentry))
 		goto fail;
 	connection->debugfs_conn_callback_history = dentry;
+
+	dentry = debugfs_create_file("oldest_requests", S_IRUSR|S_IRGRP,
+			connection->debugfs_conn, connection,
+			&connection_oldest_requests_fops);
+	if (IS_ERR_OR_NULL(dentry))
+		goto fail;
+	connection->debugfs_conn_oldest_requests = dentry;
 	return;
 
 fail: