Give an IDB and an NRB as examples of the third type of block.

There are events, there are reports, and there are "here's metadata that
doesn't correspond to something that happened at this point in the
capture"; IDBs and NRBs are the third type.

Change-Id: I89e4f9bf51dc1be5766e8df61c6337ed3e484577
Reviewed-on: https://code.wireshark.org/review/25587
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 16 insertions, 0 deletions

diff --git a/wiretap/wtap.h b/wiretap/wtap.h
index 96854f8001..9dbe6fc4f0 100644
--- a/wiretap/wtap.h
+++ b/wiretap/wtap.h
@@ -1237,6 +1237,22 @@ union wtap_pseudo_header {
  * information in them stored somewhere, and used somewhere, whether
  * it's just used when saving the file in its native format or also
  * used to parse *other* file-type-specific records.
+ *
+ * These would be similar to, for example, pcapng Interface Description
+ * Blocks, for which the position within the file is significant only
+ * in that an IDB for an interface must appear before any packets from
+ * the interface; the fact that an IDB appears at some point doesn't
+ * necessarily mean something happened in the capture at that point.
+ * Name Resolution Blocks are another example of such a record.
+ *
+ * (XXX - if you want to have a record that says "this interface first
+ * showed up at this time", that needs to be a separate record type
+ * from the IDB.  We *could* add a "New Interface Description Block",
+ * with a time stamp, for that purpose, but we'd *still* have to
+ * provide IDBs for those interfaces, for compatibility with programs
+ * that don't know about the NIDB.  An ISB with only an isb_starttime
+ * option would suffice for this purpose, so nothing needs to be
+ * added to pcapng for this.)
  */
 #define REC_TYPE_PACKET               0    /**< packet */
 #define REC_TYPE_FT_SPECIFIC_EVENT    1    /**< file-type-specific event */