Change the definition of struct if_data's member ifi_epoch from wall

clock time to uptime because wall clock time may go backwards.

This is a change in the API which will impact SNMP agents who are using
ifi_epoch to set RFC2233's ifCounterDiscontinuityTime.  None are know to
exist today.  This will not impact applications that are using the
<index, epoch> tuple to verify interface uniqueness except that it
eliminates a race which could lead to a false assumption of uniqueness.

Because this is a behavior change, bump __FreeBSD_version.

Discussed with:	re (jhb, scottl)
MFC after:	3 days
Pointed out by:	pkh (way back at EuroBSDCon)
Pointy hat:	brooks

5 files changed, 12 insertions, 4 deletions

diff --git a/UPDATING b/UPDATING
index d7bf823..daa6f78 100644
--- a/UPDATING
+++ b/UPDATING
@@ -21,6 +21,14 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 6.x IS SLOW:
 	developers choose to disable these features on build machines
 	to maximize performance.
 
+20050225:
+	The ifi_epoch member of struct if_data has been changed to
+	contain the uptime at which the interface was created or the
+	statistics zeroed rather then the wall clock time because
+	wallclock time may go backwards.  This should have no impact
+	unless an snmp implementation is using this value (I know of
+	none at this point.)
+
 20050223:
 	The layout of struct image_params has changed. You have to
 	recompile all compatibility modules (linux, svr4, etc) for use
diff --git a/share/man/man9/ifnet.9 b/share/man/man9/ifnet.9
index 86c9724..9eeb34b 100644
--- a/share/man/man9/ifnet.9
+++ b/share/man/man9/ifnet.9
@@ -729,7 +729,7 @@ the current value of
 .Va if_capenable .
 .It ifi_epoch
 .Pq Vt time_t
-The time the interface was attached or the last time the statistics
+The system uptime when interface was attached or the statistics
 below were reset.
 This is intended to be used to set the SNMP variable
 .Va ifCounterDiscontinuityTime .
diff --git a/sys/net/if.c b/sys/net/if.c
index 82d078e..d257919 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -392,7 +392,7 @@ if_attach(struct ifnet *ifp)
 	TAILQ_INIT(&ifp->if_multiaddrs);
 	knlist_init(&ifp->if_klist, NULL);
 	getmicrotime(&ifp->if_lastchange);
-	ifp->if_data.ifi_epoch = time_second;
+	ifp->if_data.ifi_epoch = time_uptime;
 
 #ifdef MAC
 	mac_init_ifnet(ifp);
diff --git a/sys/net/if.h b/sys/net/if.h
index 0fa63d7..b4d5bdb 100644
--- a/sys/net/if.h
+++ b/sys/net/if.h
@@ -102,7 +102,7 @@ struct if_data {
 	u_long	ifi_iqdrops;		/* dropped on input, this interface */
 	u_long	ifi_noproto;		/* destined for unsupported protocol */
 	u_long	ifi_hwassist;		/* HW offload capabilities */
-	time_t	ifi_epoch;		/* time of attach or stat reset */
+	time_t	ifi_epoch;		/* uptime at attach or stat reset */
 #ifdef __alpha__
 	u_int	ifi_timepad;		/* time_t is int, not long on alpha */
 #endif
diff --git a/sys/sys/param.h b/sys/sys/param.h
index faa401b..59d10df 100644
--- a/sys/sys/param.h
+++ b/sys/sys/param.h
@@ -57,7 +57,7 @@
  *		is created, otherwise 1.
  */
 #undef __FreeBSD_version
-#define __FreeBSD_version 600014	/* Master, propagated to newvers */
+#define __FreeBSD_version 600015	/* Master, propagated to newvers */
 
 #ifndef LOCORE
 #include <sys/types.h>