rfnoc: noc_block_base: Throw if set_mtu_forwarding_policy() called multiply

1 files changed, 6 insertions, 1 deletions

diff --git a/host/include/uhd/rfnoc/noc_block_base.hpp b/host/include/uhd/rfnoc/noc_block_base.hpp
index 0514849c4..dbb20b8d2 100644
--- a/host/include/uhd/rfnoc/noc_block_base.hpp
+++ b/host/include/uhd/rfnoc/noc_block_base.hpp
@@ -204,7 +204,9 @@ protected:
      * noc_block_base. If an RFNoC block subclassing noc_block_base wants to
      * modify the MTU forwarding policy, it would typically call this function
      * in its constructor. Once set, however, the MTU forwarding policy cannot
-     * be changed.
+     * be changed. This represents a change in behaviour from UHD 4.0.
+     * Violations of this restriction will result in a uhd::runtime_error being
+     * thrown.
      */
     void set_mtu_forwarding_policy(const forwarding_policy_t policy);
 
@@ -294,6 +296,9 @@ private:
     //! Forwarding policy for the MTU properties
     forwarding_policy_t _mtu_fwd_policy = forwarding_policy_t::DROP;
 
+    //! Flag indicating if MTU forwarding property has been set yet
+    bool _mtu_fwd_policy_set = false;
+
     //! Container for the 'mtu' property. This will hold one edge property
     // for all in- and output edges.
     std::vector<property_t<size_t>> _mtu_props;