On Thu, Oct 02, 2025 at 08:34:09PM -0400, Jon Maloy wrote:
> We forward the incoming MAC address through the tap interface when
> receiving incoming packets from network local hosts.
> 
> This is a part of the solution to bug
> https://bugs.passt.top/show_bug.cgi?id=120
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

[snip]
> @@ -801,13 +800,19 @@ static void udp_buf_sock_to_tap(const struct ctx *c, int s, int n,
>  				flow_sidx_t tosidx)
>  {
>  	const struct flowside *toside = flowside_at_sidx(tosidx);
> +	struct udp_flow *uflow = udp_at_sidx(tosidx);
> +	uint8_t *omac = uflow->f.tap_omac;
>  	int i;
>  
>  	if ((n = udp_sock_recv(c, s, udp_mh_recv, n)) <= 0)
>  		return;
>  
> +	/* Find if neighbour table has a recorded MAC address */
> +	if (MAC_IS_UNDEF(omac))
> +		fwd_neigh_mac_get(c, &toside->oaddr, omac);

Uh oh.  Here you're looking up based on a guest side address, whereas
other places are looking up based on a host side address.  You need to
pick one.

> +
>  	for (i = 0; i < n; i++)
> -		udp_tap_prepare(udp_mh_recv, i, toside, false);
> +		udp_tap_prepare(udp_mh_recv, i, omac, toside, false);
>  
>  	tap_send_frames(c, &udp_l2_iov[0][0], UDP_NUM_IOVS, n);
>  }
> diff --git a/udp.h b/udp.h
> index 8f8531a..dd6e5ad 100644
> --- a/udp.h
> +++ b/udp.h
> @@ -21,7 +21,7 @@ int udp_sock_init(const struct ctx *c, int ns, const union inany_addr *addr,
>  		  const char *ifname, in_port_t port);
>  int udp_init(struct ctx *c);
>  void udp_timer(struct ctx *c, const struct timespec *now);
> -void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s);
> +void udp_update_l2_buf(const unsigned char *eth_d);
>  
>  /**
>   * union udp_listen_epoll_ref - epoll reference for "listening" UDP sockets
> -- 
> 2.50.1
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson