netdev - Re: [PATCH net 2/2] selftests: fib_nexthops: Add test case for ipv4 multi nexthops

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Message-ID: <willemdebruijn.kernel.2568c56f18788@gmail.com>
Date: Sat, 13 Dec 2025 16:18:08 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, 
 "David S. Miller" <davem@...emloft.net>, 
 David Ahern <dsahern@...nel.org>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, 
 Willem de Bruijn <willemb@...gle.com>, 
 Jakub Kicinski <kuba@...nel.ord>
Cc: Shuah Khan <shuah@...nel.org>, 
 Ido Schimmel <idosch@...dia.com>, 
 netdev@...r.kernel.org, 
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Subject: Re: [PATCH net 2/2] selftests: fib_nexthops: Add test case for ipv4
 multi nexthops

Vadim Fedorenko wrote:
> The test checks that with multi nexthops route the preferred route is the
> one which matches source ip. In case when source ip is on loopback, it
> checks that the routes are balanced.

are balanced [across .. ]

> 
> Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
> ---
>  tools/testing/selftests/net/fib_nexthops.sh | 85 +++++++++++++++++++++
>  1 file changed, 85 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/fib_nexthops.sh b/tools/testing/selftests/net/fib_nexthops.sh
> index 2b0a90581e2f..9d6f57399a73 100755
> --- a/tools/testing/selftests/net/fib_nexthops.sh
> +++ b/tools/testing/selftests/net/fib_nexthops.sh
> @@ -31,6 +31,7 @@ IPV4_TESTS="
>  	ipv4_compat_mode
>  	ipv4_fdb_grp_fcnal
>  	ipv4_mpath_select
> +	ipv4_mpath_select_nogrp
>  	ipv4_torture
>  	ipv4_res_torture
>  "
> @@ -375,6 +376,17 @@ check_large_res_grp()
>  	log_test $? 0 "Dump large (x$buckets) nexthop buckets"
>  }
>  
> +get_route_dev_src()
> +{
> +	local pfx="$1"
> +	local src="$2"
> +	local out
> +
> +	if out=$($IP -j route get "$pfx" from "$src" | jq -re ".[0].dev"); then
> +		echo "$out"
> +	fi
> +}
> +
>  get_route_dev()
>  {
>  	local pfx="$1"
> @@ -641,6 +653,79 @@ ipv4_fdb_grp_fcnal()
>  	$IP link del dev vx10
>  }
>  
> +ipv4_mpath_select_nogrp()

There is more going on than just not using the group feature.

Would it make sense to split this into two test patches, a base test
and a follow-on that extends with the loopback special case?

> +{
> +	local rc dev match h addr
> +
> +	echo
> +	echo "IPv4 multipath selection no group"
> +	echo "------------------------"
> +	if [ ! -x "$(command -v jq)" ]; then
> +		echo "SKIP: Could not run test; need jq tool"
> +		return $ksft_skip
> +	fi
> +
> +	IP="ip -netns $peer"
> +	# Use status of existing neighbor entry when determining nexthop for
> +	# multipath routes.
> +	local -A gws
> +	gws=([veth2]=172.16.1.1 [veth4]=172.16.2.1)
> +	local -A other_dev
> +	other_dev=([veth2]=veth4 [veth4]=veth2)
> +	local -A local_ips
> +	local_ips=([veth2]=172.16.1.2 [veth4]=172.16.2.2 [veth5]=172.16.100.1)

Why do both loopback and veth5 exist with the same local ip. Can this just be lo?
> +	local -A route_devs
> +	route_devs=([veth2]=0 [veth4]=0)
> +
> +	run_cmd "$IP address add 172.16.100.1/32 dev lo"
> +	run_cmd "$IP ro add 172.16.102.0/24 nexthop via ${gws['veth2']} dev veth2 nexthop via ${gws['veth4']} dev veth4"
> +	rc=0
> +	for dev in veth2 veth4; do
> +		match=0
> +		from_ip="${local_ips[$dev]}"
> +		for h in {1..254}; do
> +			addr="172.16.102.$h"
> +			if [ "$(get_route_dev_src "$addr" "$from_ip")" = "$dev" ]; then
> +				match=1
> +				break
> +			fi
> +		done
> +		if (( match == 0 )); then
> +			echo "SKIP: Did not find a route using device $dev"
> +			return $ksft_skip
> +		fi
> +		run_cmd "$IP neigh add ${gws[$dev]} dev $dev nud failed"
> +		if ! check_route_dev "$addr" "${other_dev[$dev]}"; then
> +			rc=1
> +			break
> +		fi
> +		run_cmd "$IP neigh del ${gws[$dev]} dev $dev"
> +	done
> +
> +	log_test $rc 0 "Use valid neighbor during multipath selection"
> +
> +	from_ip="${local_ips["veth5"]}"
> +	for h in {1..254}; do
> +		addr="172.16.102.$h"
> +		route_dev=$(get_route_dev_src "$addr" "$from_ip")
> +		route_devs[$route_dev]=1
> +	done
> +	for dev in veth2 veth4; do
> +		if [ ${route_devs[$dev]} -eq 0 ]; then
> +			rc=1
> +			break;
> +		fi
> +	done
> +
> +	log_test $rc 0 "Use both neighbors during multipath selection"
> +
> +	run_cmd "$IP neigh add 172.16.1.2 dev veth1 nud incomplete"
> +	run_cmd "$IP neigh add 172.16.2.2 dev veth3 nud incomplete"
> +	run_cmd "$IP route get 172.16.101.1"
> +	# if we did not crash, success
> +	log_test $rc 0 "Multipath selection with no valid neighbor"
> +}
> +
>  ipv4_mpath_select()
>  {
>  	local rc dev match h addr
> -- 
> 2.47.3
>