Introduce #defines for exponential backoff, explain where they come

from and explain why we are a bit more agressive during startup.
While here make the math a bit easier on the eyes.

diff --git a/sbin/dhcpleased/engine.c b/sbin/dhcpleased/engine.c
index 092aa45..58c66de 100644 (file)
--- a/sbin/dhcpleased/engine.c
+++ b/sbin/dhcpleased/engine.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: engine.c,v 1.2 2021/02/27 10:07:41 florian Exp $      */
+/*     $OpenBSD: engine.c,v 1.3 2021/02/28 15:26:26 florian Exp $      */
 
 /*
  * Copyright (c) 2017, 2021 Florian Obser <florian@openbsd.org>
@@ -50,7 +50,13 @@
 #include "dhcpleased.h"
 #include "engine.h"
 
-#define        MINIMUM(a, b)   (((a) < (b)) ? (a) : (b))
+/*
+ * RFC 2131 4.1 p23 has "SHOULD be 4 seconds", we are a bit more aggressive,
+ * networks are faster these days.
+ */
+#define        START_EXP_BACKOFF        1
+#define        MAX_EXP_BACKOFF         64 /* RFC 2131 4.1 p23 */
+#define        MINIMUM(a, b)           (((a) < (b)) ? (a) : (b))
 
 enum if_state {
        IF_DOWN,
@@ -1087,32 +1093,29 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state)
                            sizeof(iface->nameservers));
                }
                if (old_state == IF_INIT) {
-                       iface->timo.tv_sec *= 2;
-                       if (iface->timo.tv_sec > 64)
-                               iface->timo.tv_sec = 64;
+                       if (iface->timo.tv_sec < MAX_EXP_BACKOFF)
+                               iface->timo.tv_sec *= 2;
                } else
-                       iface->timo.tv_sec = 1;
+                       iface->timo.tv_sec = START_EXP_BACKOFF;
                request_dhcp_discover(iface);
                break;
        case IF_REBOOTING:
                if (old_state == IF_REBOOTING) {
-                       iface->timo.tv_sec *= 2;
-                       if (iface->timo.tv_sec > 64)
-                               iface->timo.tv_sec = 64;
+                       if (iface->timo.tv_sec < MAX_EXP_BACKOFF)
+                               iface->timo.tv_sec *= 2;
                } else {
                        /* make sure we send broadcast */
                        iface->dhcp_server.s_addr = INADDR_ANY;
-                       iface->timo.tv_sec = 1;
+                       iface->timo.tv_sec = START_EXP_BACKOFF;
                }
                request_dhcp_request(iface);
                break;
        case IF_REQUESTING:
                if (old_state == IF_REQUESTING) {
-                       iface->timo.tv_sec *= 2;
-                       if (iface->timo.tv_sec > 64)
-                               iface->timo.tv_sec = 64;
+                       if (iface->timo.tv_sec < MAX_EXP_BACKOFF)
+                               iface->timo.tv_sec *= 2;
                } else
-                       iface->timo.tv_sec = 1;
+                       iface->timo.tv_sec = START_EXP_BACKOFF;
                request_dhcp_request(iface);
                break;
        case IF_BOUND:
@@ -1176,13 +1179,13 @@ iface_timeout(int fd, short events, void *arg)
                state_transition(iface, IF_INIT);
                break;
        case IF_REBOOTING:
-               if (iface->timo.tv_sec >= 64)
+               if (iface->timo.tv_sec >= MAX_EXP_BACKOFF)
                        state_transition(iface, IF_INIT);
                else
                        state_transition(iface, IF_REBOOTING);
                break;
        case IF_REQUESTING:
-               if (iface->timo.tv_sec >= 64)
+               if (iface->timo.tv_sec >= MAX_EXP_BACKOFF)
                        state_transition(iface, IF_INIT);
                else
                        state_transition(iface, IF_REQUESTING);