From 74ab49bec1f5d0ba7e41b395b1ddb6df8f2e2298 Mon Sep 17 00:00:00 2001
From: guy <guy>
Date: Thu, 14 Sep 2000 09:49:28 +0000
Subject: Add comments telling people not to gratuitously change the capture
 file format (file header or per-packet header format, or interpretation of
 any of the fields in those headers) without getting a new magic number from
 "tcpdump-workers@tcpdump.org", and to make sure that libpcap can still read
 files with the existing magic numbers, not just files with the new magic
 number and record formats.

(There have been at least three libpcap changes I know of that have
changed the header formats, or the interpretation of fields in those
headers, without changing the magic number.  I would like not to ever
have any other such changes happen ever again.)
---
 pcap.h | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

(limited to 'pcap.h')

diff --git a/pcap.h b/pcap.h
index ac9f05c..4bf8596 100644
--- a/pcap.h
+++ b/pcap.h
@@ -30,7 +30,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- * @(#) $Header: /tcpdump/master/libpcap/pcap.h,v 1.24 2000-07-29 07:36:43 guy Exp $ (LBL)
+ * @(#) $Header: /tcpdump/master/libpcap/pcap.h,v 1.25 2000-09-14 09:49:29 guy Exp $ (LBL)
  */
 
 #ifndef lib_pcap_h
@@ -69,6 +69,27 @@ typedef struct pcap_dumper pcap_dumper_t;
  * of the flags used in the printout phases of tcpdump.
  * Many fields here are 32 bit ints so compilers won't insert unwanted
  * padding; these files need to be interchangeable across architectures.
+ *
+ * Do not change the format of this structure, in any way (this includes
+ * changes that only affect the length of fields in this structure).
+ * Instead:
+ *
+ *	introduce a new structure for the new format;
+ *
+ *	send mail to "tcpdump-workers@tcpdump.org", requesting a new
+ *	magic number for your new capture file format, and, when
+ *	you get the new magic number, put it in "savefile.c";
+ *
+ *	use that magic number for save files with the changed file
+ *	header;
+ *
+ *	make the code in "savefile.c" capable of reading files with
+ *	the old file header as well as files with the new file header
+ *	(using the magic number to determine the header format).
+ *
+ * Then supply the changes to "patches@tcpdump.org", so that future
+ * versions of libpcap and programs that use it (such as tcpdump) will
+ * be able to read your new capture file format.
  */
 struct pcap_file_header {
 	bpf_u_int32 magic;
-- 
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