From aabfb8a94dafb361af8b2d093471958f19250813 Mon Sep 17 00:00:00 2001
From: Michael Brown <mcb30@ipxe.org>
Date: Mon, 5 Jan 2026 15:46:52 +0000
Subject: [PATCH] [neighbour] Use discovery protocol field to identify
 incomplete neighbours

Use the discovery protocol pointer field (rather than the running
state of the discovery timer) to determine whether or not neighbour
discovery is ongoing, as a precursor to allowing the timer to be
(ab)used for adding deliberate latency to transmitted packets.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/include/ipxe/neighbour.h | 15 ++-------------
 src/net/neighbour.c          | 21 +++++++++++++++------
 src/usr/neighmgmt.c          |  5 ++---
 3 files changed, 19 insertions(+), 22 deletions(-)

diff --git a/src/include/ipxe/neighbour.h b/src/include/ipxe/neighbour.h
index 1ca0ee333..7e7fac277 100644
--- a/src/include/ipxe/neighbour.h
+++ b/src/include/ipxe/neighbour.h
@@ -49,9 +49,9 @@ struct neighbour {
 	/** Link-layer destination address */
 	uint8_t ll_dest[MAX_LL_ADDR_LEN];
 
-	/** Neighbour discovery protocol (if any) */
+	/** Neighbour discovery protocol (if discovery is ongoing) */
 	struct neighbour_discovery *discovery;
-	/** Network-layer source address (if any) */
+	/** Network-layer source address (for discovery requests) */
 	uint8_t net_source[MAX_NET_ADDR_LEN];
 	/** Retransmission timer */
 	struct retry_timer timer;
@@ -60,17 +60,6 @@ struct neighbour {
 	struct list_head tx_queue;
 };
 
-/**
- * Test if neighbour cache entry has a valid link-layer address
- *
- * @v neighbour		Neighbour cache entry
- * @ret has_ll_dest	Neighbour cache entry has a valid link-layer address
- */
-static inline __attribute__ (( always_inline )) int
-neighbour_has_ll_dest ( struct neighbour *neighbour ) {
-	return ( ! timer_running ( &neighbour->timer ) );
-}
-
 extern struct list_head neighbours;
 
 extern int neighbour_tx ( struct io_buffer *iobuf, struct net_device *netdev,
diff --git a/src/net/neighbour.c b/src/net/neighbour.c
index 253cdc0e6..908f8e4b2 100644
--- a/src/net/neighbour.c
+++ b/src/net/neighbour.c
@@ -186,6 +186,9 @@ static void neighbour_discovered ( struct neighbour *neighbour,
 	/* Stop retransmission timer */
 	stop_timer ( &neighbour->timer );
 
+	/* Mark discovery as complete */
+	neighbour->discovery = NULL;
+
 	/* Transmit any packets in queue.  Take out a temporary
 	 * reference on the entry to prevent it from going out of
 	 * scope during the call to net_tx().
@@ -300,6 +303,7 @@ int neighbour_tx ( struct io_buffer *iobuf, struct net_device *netdev,
 		   struct neighbour_discovery *discovery,
 		   const void *net_source ) {
 	struct neighbour *neighbour;
+	int rc;
 
 	/* Find or create neighbour cache entry */
 	neighbour = neighbour_find ( netdev, net_protocol, net_dest );
@@ -310,19 +314,24 @@ int neighbour_tx ( struct io_buffer *iobuf, struct net_device *netdev,
 		neighbour_discover ( neighbour, discovery, net_source );
 	}
 
-	/* If a link-layer address is available then transmit
-	 * immediately, otherwise queue for later transmission.
+	/* If discovery is still in progress then queue for later
+	 * transmission.
 	 */
-	if ( neighbour_has_ll_dest ( neighbour ) ) {
-		return net_tx ( iobuf, netdev, net_protocol, neighbour->ll_dest,
-				netdev->ll_addr );
-	} else {
+	if ( neighbour->discovery ) {
 		DBGC2 ( neighbour, "NEIGHBOUR %s %s %s deferring packet\n",
 			netdev->name, net_protocol->name,
 			net_protocol->ntoa ( net_dest ) );
 		list_add_tail ( &iobuf->list, &neighbour->tx_queue );
 		return 0;
 	}
+
+	/* Otherwise, transmit immediately */
+	if ( ( rc = net_tx ( iobuf, netdev, net_protocol, neighbour->ll_dest,
+			     netdev->ll_addr ) ) != 0 ) {
+		return rc;
+	}
+
+	return 0;
 }
 
 /**
diff --git a/src/usr/neighmgmt.c b/src/usr/neighmgmt.c
index 9fd88f82b..fcdcbbfbb 100644
--- a/src/usr/neighmgmt.c
+++ b/src/usr/neighmgmt.c
@@ -50,9 +50,8 @@ void nstat ( void ) {
 		printf ( "%s %s %s is %s %s", netdev->name, net_protocol->name,
 			 net_protocol->ntoa ( neighbour->net_dest ),
 			 ll_protocol->name,
-			 ( neighbour_has_ll_dest ( neighbour ) ?
-			   ll_protocol->ntoa ( neighbour->ll_dest ) :
-			   "(incomplete)" ) );
+			 ( neighbour->discovery ? "(incomplete)" :
+			   ll_protocol->ntoa ( neighbour->ll_dest ) ) );
 		if ( neighbour->discovery )
 			printf ( " (%s)", neighbour->discovery->name );
 		printf ( "\n" );