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+Buffer metadata change tracker
+==============================
+
+Introduction
+------------
+
+The mdata plugin uses the vlib main loop “before” performance counter
+hook to snapshoot buffer metadata before calling the node dispatch
+function. Similarly, the plugin uses the main loop “after” hook to
+compare a vectors’ worth of buffer metadata after the fact.
+
+The comparison function is a simple octet-by-octet A != B check. We
+accumulate changed octets per-node across the entire run, using a single
+spinlock-protected accumulator.
+
+The “show buffer metadata” command produces a report of all fields whose
+values are changed by nodes visited during a given run.
+
+Since many fields in the vnet_buffer_opaque_t are union members, it may
+appear that a certain node changes numerous fields. The entire point of
+the exercise is to warn developers that if a packet visits node N, data
+placed into opaque union field F *will* be affected.
+
+One should never assume much about buffer metadata immutability across
+arbitrary subgraphs. This tool generates accurate reports, to the extent
+that one exercises the required subgraph trajectories.