From: Paul Donald <newtwen+github@gmail.com>
Date: Sun, 2 Nov 2025 16:40:14 +0000 (+0100)
Subject: netlink: Store interface MTU at link change
X-Git-Url: http://git.openwrt.org/?a=commitdiff_plain;h=ee4f0df6bd686bf58594fca394dfaf3ba153d92c;p=project%2Fodhcpd.git

netlink: Store interface MTU at link change

This is used for clamping MTU values.

Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Link: https://github.com/openwrt/odhcpd/pull/296
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---

diff --git a/src/netlink.c b/src/netlink.c
index 5b3dc66..6de9ae7 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -257,6 +257,13 @@ static int handle_rtm_link(struct nlmsghdr *hdr)
 
 		iface->ifflags = ifi->ifi_flags;
 
+		/* store current MTU if available */
+		if (nla[IFLA_MTU]) {
+			iface->if_mtu = nla_get_u32(nla[IFLA_MTU]);
+			debug("Netlink setting interface '%s' if_mtu MTU to %d",
+					iface->name, iface->if_mtu);
+		}
+
 		/*
 		 * Assume for link event of the same index, that link changed
 		 * and reload services to enable or disable them based on the
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 55107e5..e503029 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -333,6 +333,7 @@ struct interface {
 	int ifindex;
 	char *ifname;
 	const char *name;
+	uint32_t if_mtu;
 
 	// IPv6 runtime data
 	struct odhcpd_ipaddr *addr6;