Further emphasize "don't change these structure layouts".

And don't change #defines for structure field values, either.

diff --git a/rpcap-protocol.h b/rpcap-protocol.h
index 47ab5757f2dc5fbc51ef37ffc4c1762743a0db5c..af966a7b0cf459f5f682399c5372c86abe8a2eed 100644 (file)
--- a/rpcap-protocol.h
+++ b/rpcap-protocol.h
@@ -200,6 +200,12 @@
  * for better alignment.
  * These structures have been created in order to be correctly aligned to
  * a 32-bit boundary, but be careful in any case.
+ *
+ * The layout of these structures MUST not be changed.  If a packet
+ * format is different in different versions of the protocol, versions
+ * of the structure should be provided for all the different versions or
+ * version ranges (if more than one version of the protocol has the same
+ * layout) that we support.
  */
 
 /*
@@ -406,7 +412,12 @@ struct rpcap_sampling
        uint32 value;   /* Parameter related to the sampling method */
 };
 
-/* Messages field coding */
+/*
+ * Messages field coding.
+ *
+ * These values are used in messages sent over the network, and MUST
+ * not be changed.
+ */
 #define RPCAP_MSG_IS_REPLY             0x080   /* Flag indicating a reply */
 
 #define RPCAP_MSG_ERROR                        1       /* Message that keeps an error notification */
@@ -438,7 +449,12 @@ struct rpcap_sampling
 
 #define RPCAP_UPDATEFILTER_BPF 1                       /* This code tells us that the filter is encoded with the BPF/NPF syntax */
 
-/* Network error codes */
+/*
+ * Network error codes.
+ *
+ * These values are used in messages sent over the network, and MUST
+ * not be changed.
+ */
 #define PCAP_ERR_NETW          1       /* Network error */
 #define PCAP_ERR_INITTIMEOUT   2       /* The RPCAP initial timeout has expired */
 #define PCAP_ERR_AUTH          3       /* Generic authentication error */