Revert r239356 and use an alternate algorithm.

First, don't exit when the link goes down on an interface.  Instead,
teach dhclient to track changes in link state and to enter the reboot
state when the link on an interface goes up causing dhclient to attempt
to renew its existing lease.

Second, remove the change I added to clear the old lease when dhclient
exits due to an error (such as ifconfig down).  If an interface is
using autoconfiguration it should keep its autoconfiguration as much as
possible.  If the next time it needs a configuration it is able to reuse
the previous autoconfiguration, then leaving the settings intact allows
existing connections to survive temporary outages, etc.

PR:		bin/166656
MFC after:	1 month

2 files changed, 11 insertions, 6 deletions

diff --git a/sbin/dhclient/dhclient.c b/sbin/dhclient/dhclient.c
index 7260d3f..f71c8c8 100644
--- a/sbin/dhclient/dhclient.c
+++ b/sbin/dhclient/dhclient.c
@@ -218,6 +218,7 @@ routehandler(struct protocol *p)
 	struct sockaddr *sa;
 	struct iaddr a;
 	ssize_t n;
+	int linkstat;
 
 	n = read(routefd, &msg, sizeof(msg));
 	rtm = (struct rt_msghdr *)msg;
@@ -278,10 +279,14 @@ routehandler(struct protocol *p)
 			    ifi->name);
 			goto die;
 		}
-		if (!interface_link_status(ifi->name)) {
-			warning("Interface %s is down, dhclient exiting",
-			    ifi->name);
-			goto die;
+		linkstat = interface_link_status(ifi->name);
+		if (linkstat != ifi->linkstat) {
+			debug("%s link state %s -> %s", ifi->name,
+			    ifi->linkstat ? "up" : "down",
+			    linkstat ? "up" : "down");
+			ifi->linkstat = linkstat;
+			if (linkstat)
+				state_reboot(ifi);
 		}
 		break;
 	case RTM_IFANNOUNCE:
@@ -321,8 +326,6 @@ routehandler(struct protocol *p)
 
 die:
 	script_init("FAIL", NULL);
-	if (ifi->client->active)
-		script_write_params("old_", ifi->client->active);
 	if (ifi->client->alias)
 		script_write_params("alias_", ifi->client->alias);
 	script_go();
@@ -437,6 +440,7 @@ main(int argc, char *argv[])
 		}
 		fprintf(stderr, " got link\n");
 	}
+	ifi->linkstat = 1;
 
 	if ((nullfd = open(_PATH_DEVNULL, O_RDWR, 0)) == -1)
 		error("cannot open %s: %m", _PATH_DEVNULL);
diff --git a/sbin/dhclient/dhcpd.h b/sbin/dhclient/dhcpd.h
index 1334a7c..4762cbd 100644
--- a/sbin/dhclient/dhcpd.h
+++ b/sbin/dhclient/dhcpd.h
@@ -208,6 +208,7 @@ struct interface_info {
 	int			 errors;
 	int			 dead;
 	u_int16_t		 index;
+	int			 linkstat;
 };
 
 struct timeout {