From: David Härdeman <david@hardeman.nu>
Date: Wed, 8 Oct 2025 13:46:24 +0000 (+0200)
Subject: dhcpv4: dhcpv4_assign() - explain address assignment
X-Git-Url: http://git.openwrt.org/%22https:/collectd.org//%22http:/www.crowdsec.net/%22/%22https:/collectd.org/%22http:/www.crowdsec.net/%22?a=commitdiff_plain;h=3ad54baa4adc0d6d102ccdc82f8b1f7439059f6e;p=project%2Fodhcpd.git

dhcpv4: dhcpv4_assign() - explain address assignment

Add some debug statements that also serve as comments explaining the logic
of dhcpv4_assign() and which make it easier to understand why a
requested address was not provided.

Signed-off-by: David Härdeman <david@hardeman.nu>
Link: https://github.com/openwrt/odhcpd/pull/286
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---

diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 3fc1a3d..173457a 100644
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -367,43 +367,48 @@ static bool dhcpv4_assign(struct interface *iface, struct dhcp_assignment *a,
 	uint32_t end = ntohl(iface->dhcpv4_end_ip.s_addr);
 	uint32_t count = end - start + 1;
 	uint32_t seed = 0;
-	bool assigned;
 	char ipv4_str[INET_ADDRSTRLEN];
 
 	/* Preconfigured IP address by static lease */
 	if (a->addr) {
-		assigned = dhcpv4_insert_assignment(&iface->dhcpv4_assignments,
-						    a, a->addr);
-
-		if (assigned)
-			debug("Assigning static IP: %s",
+		if (!dhcpv4_insert_assignment(&iface->dhcpv4_assignments, a, a->addr)) {
+			error("The static IP address is already assigned: %s",
 			      inet_ntop(AF_INET, &a->addr, ipv4_str, sizeof(ipv4_str)));
+			return false;
+		}
 
-		return assigned;
+		debug("Assigned static IP address: %s",
+		      inet_ntop(AF_INET, &a->addr, ipv4_str, sizeof(ipv4_str)));
+		return true;
 	}
 
-	/* try to assign the IP the client asked for */
-	if (start <= ntohl(raddr) && ntohl(raddr) <= end &&
-	    !config_find_lease_by_ipaddr(raddr)) {
-		assigned = dhcpv4_insert_assignment(&iface->dhcpv4_assignments,
-						    a, raddr);
-
-		if (assigned) {
-			debug("Assigning the IP the client asked for: %s",
-			      inet_ntop(AF_INET, &a->addr, ipv4_str, sizeof(ipv4_str)));
-			return true;
-		}
+	/* The client asked for a specific address, let's try... */
+	if (ntohl(raddr) < start || ntohl(raddr) > end) {
+		debug("The requested IP address is outside the pool: %s",
+		      inet_ntop(AF_INET, &raddr, ipv4_str, sizeof(ipv4_str)));
+	} else if (config_find_lease_by_ipaddr(raddr)) {
+		debug("The requested IP address is statically assigned: %s",
+		      inet_ntop(AF_INET, &raddr, ipv4_str, sizeof(ipv4_str)));
+	} else if (!dhcpv4_insert_assignment(&iface->dhcpv4_assignments, a, raddr)) {
+		debug("The requested IP address is already assigned: %s",
+		      inet_ntop(AF_INET, &raddr, ipv4_str, sizeof(ipv4_str)));
+	} else {
+		debug("Assigned the requested IP address: %s",
+		      inet_ntop(AF_INET, &a->addr, ipv4_str, sizeof(ipv4_str)));
+		return true;
 	}
 
-	/* Seed RNG with checksum of hwaddress */
+	/* Ok, we'll have to pick an address for the client... */
 	for (size_t i = 0; i < sizeof(a->hwaddr); ++i) {
-		/* Knuth's multiplicative method */
+		/* ...hash the hwaddr (Knuth's multiplicative method)... */
 		uint8_t o = a->hwaddr[i];
-		seed += (o*2654435761) % UINT32_MAX;
+		seed += (o * 2654435761) % UINT32_MAX;
 	}
 
+	/* ...use it to seed the RNG... */
 	srand(seed);
 
+	/* ...and try a bunch of times to assign a randomly chosen address */
 	for (uint32_t i = 0, try = (((uint32_t)rand()) % count) + start; i < count;
 	     ++i, try = (((try - start) + 1) % count) + start) {
 		uint32_t n_try = htonl(try);
@@ -411,14 +416,10 @@ static bool dhcpv4_assign(struct interface *iface, struct dhcp_assignment *a,
 		if (config_find_lease_by_ipaddr(n_try))
 			continue;
 
-		assigned = dhcpv4_insert_assignment(&iface->dhcpv4_assignments,
-						    a, n_try);
-
-		if (assigned) {
-			debug("Assigning mapped IP: %s (try %u of %u)",
+		if (dhcpv4_insert_assignment(&iface->dhcpv4_assignments, a, n_try)) {
+			debug("Assigned IP adress from pool: %s (succeeded on attempt %u of %u)",
 			      inet_ntop(AF_INET, &a->addr, ipv4_str, sizeof(ipv4_str)),
 			      i + 1, count);
-
 			return true;
 		}
 	}