From 7d1b081dcb1b4616307e871e760d6a080d843856 Mon Sep 17 00:00:00 2001
From: =?utf8?q?David=20H=C3=A4rdeman?= <david@hardeman.nu>
Date: Fri, 10 Oct 2025 19:55:36 +0200
Subject: [PATCH] dhcpv4: lazy store statefiles
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Currently, the dhcpv4 server saves the statefile on every change and
also calls the leasetrigger script every time the statefile is updated
(which triggers a dnsmasq reload).

In addition, odhcpd wakes up every second (see dhcpv4_valid_until_cb())
to go through all existing leases to see if any lease has expired.

With this change, the wakeups are reduced to every 5 seconds, and the
statefile is only written (if necessary) during that wakeup.

Before this change (without any leasetrigger, test on my laptop, not a
real OpenWrt device):

$ time sudo ./build/dhcpdig -4 benchmark foo-client

Thread[**]: req 10000101/0 rel 10000101/0 rep 10000101/0

real	55m29.406s
user	0m0.005s
sys	0m0.010s

(This is a simple benchmark tool I wrote, it runs 10 threads which
divide the DHVPv4 pool into 10 chunks and then performs 1 million random
addr req/release per thread in a loop).

After this change:

$ time sudo ./build/dhcpdig -4 benchmark foo-client

Thread[**]: req 10000101/0 rel 10000101/0 rep 10000101/0

real	1m48.123s
user	0m0.005s
sys	0m0.005s

A 3082% speedup.

Signed-off-by: David Härdeman <david@hardeman.nu>
Link: https://github.com/openwrt/odhcpd/pull/298
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 src/config.c |  1 +
 src/dhcpv4.c | 23 +++++++++++++++++++++--
 src/odhcpd.h |  1 +
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/config.c b/src/config.c
index 63e3952..6917f9a 100644
--- a/src/config.c
+++ b/src/config.c
@@ -344,6 +344,7 @@ static void set_interface_defaults(struct interface *iface)
 	iface->ra_lifetime = 3 * iface->ra_maxinterval; /* RFC4861: AdvDefaultLifetime: Default: 3 * MaxRtrAdvInterval */
 	iface->ra_dns = true;
 	iface->pio_update = false;
+	iface->update_statefile = true;
 }
 
 static void clean_interface(struct interface *iface)
diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index aaf6821..d5177c6 100644
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -336,6 +336,9 @@ void dhcpv4_free_lease(struct dhcpv4_lease *lease)
 	if (lease->fr_ip)
 		dhcpv4_fr_stop(lease);
 
+	if (lease->iface)
+		lease->iface->update_statefile = true;
+
 	list_del(&lease->head);
 	if (lease->lease_cfg)
 		lease->lease_cfg->dhcpv4_lease = NULL;
@@ -407,6 +410,8 @@ static bool dhcpv4_assign(struct interface *iface, struct dhcpv4_lease *lease,
 
 		debug("Assigned static IP address: %s",
 		      inet_ntop(AF_INET, &lease->addr, ipv4_str, sizeof(ipv4_str)));
+
+		iface->update_statefile = true;
 		return true;
 	}
 
@@ -423,6 +428,7 @@ static bool dhcpv4_assign(struct interface *iface, struct dhcpv4_lease *lease,
 	} else {
 		debug("Assigned the requested IP address: %s",
 		      inet_ntop(AF_INET, &lease->addr, ipv4_str, sizeof(ipv4_str)));
+		iface->update_statefile = true;
 		return true;
 	}
 
@@ -448,6 +454,8 @@ static bool dhcpv4_assign(struct interface *iface, struct dhcpv4_lease *lease,
 			debug("Assigned IP adress from pool: %s (succeeded on attempt %u of %u)",
 			      inet_ntop(AF_INET, &lease->addr, ipv4_str, sizeof(ipv4_str)),
 			      i + 1, count);
+
+			iface->update_statefile = true;
 			return true;
 		}
 	}
@@ -624,7 +632,7 @@ dhcpv4_lease(struct interface *iface, enum dhcpv4_msg req_msg, const uint8_t *re
 		return NULL;
 	}
 
-	dhcpv6_ia_write_statefile();
+	iface->update_statefile = true;
 	return lease;
 }
 
@@ -1498,6 +1506,7 @@ static void dhcpv4_valid_until_cb(struct uloop_timeout *event)
 {
 	struct interface *iface;
 	time_t now = odhcpd_time();
+	bool update_statefile = false;
 
 	avl_for_each_element(&interfaces, iface, avl) {
 		struct dhcpv4_lease *lease, *tmp;
@@ -1511,10 +1520,20 @@ static void dhcpv4_valid_until_cb(struct uloop_timeout *event)
 						      (struct in_addr *)&lease->addr,
 						      lease->hostname, iface->ifname);
 				dhcpv4_free_lease(lease);
+				update_statefile = true;
 			}
 		}
+
+		if (iface->update_statefile) {
+			update_statefile = true;
+			iface->update_statefile = false;
+		}
 	}
-	uloop_timeout_set(event, 1000);
+
+	if (update_statefile)
+		dhcpv6_ia_write_statefile();
+
+	uloop_timeout_set(event, 5000);
 }
 
 /* Create socket and register events */
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 41c0099..2682e44 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -338,6 +338,7 @@ struct interface {
 	char *ifname;
 	const char *name;
 	uint32_t if_mtu;
+	bool update_statefile;
 
 	// IPv6 runtime data
 	struct odhcpd_ipaddr *addr6;
-- 
2.30.2