From d304fb6b38cb6ea3f9dd0ec9433581c02ecb03e1 Mon Sep 17 00:00:00 2001
From: "Nicholas J. Kain" <nicholas@kain.us>
Date: Sat, 2 Jul 2011 04:58:58 -0400
Subject: [PATCH] Only bring down the interface at startup time if it is not
 already up and running.  ndhc does its job entirely with raw sockets before a
 lease is established, so it will work just fine, and this change allows for
 the dhcp client to be re-run without causing downtime on an interface.

---
 ndhc/ndhc.c    | 3 ++-
 ndhc/netlink.c | 8 --------
 ndhc/netlink.h | 8 ++++++++
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/ndhc/ndhc.c b/ndhc/ndhc.c
index 6a9798f..a6c1596 100644
--- a/ndhc/ndhc.c
+++ b/ndhc/ndhc.c
@@ -304,7 +304,8 @@ int main(int argc, char **argv)
             "cap_net_bind_service,cap_net_broadcast,cap_net_raw=ep");
     drop_root(uid, gid);
 
-    ifchange(NULL, IFCHANGE_DECONFIG);
+    if (cs.ifsPrevState != IFS_UP)
+        ifchange(NULL, IFCHANGE_DECONFIG);
 
     do_work();
     return EXIT_SUCCESS; // Never reached.
diff --git a/ndhc/netlink.c b/ndhc/netlink.c
index 998b152..f6f6b99 100644
--- a/ndhc/netlink.c
+++ b/ndhc/netlink.c
@@ -40,14 +40,6 @@
 #include "arp.h"
 #include "log.h"
 
-enum {
-    IFS_NONE = 0,
-    IFS_UP,
-    IFS_DOWN,
-    IFS_SHUT,
-    IFS_REMOVED
-};
-
 static struct mnl_socket *mls;
 
 static void nl_close(struct client_state_t *cs)
diff --git a/ndhc/netlink.h b/ndhc/netlink.h
index 35fcedf..fe5bc30 100644
--- a/ndhc/netlink.h
+++ b/ndhc/netlink.h
@@ -22,6 +22,14 @@
 
 #include "state.h"
 
+enum {
+    IFS_NONE = 0,
+    IFS_UP,
+    IFS_DOWN,
+    IFS_SHUT,
+    IFS_REMOVED
+};
+
 int nl_open(struct client_state_t *cs);
 void handle_nl_message(struct client_state_t *cs);
 int nl_getifdata(const char *ifname, struct client_state_t *cs);