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

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Message-ID: <8cd00280-08a0-457d-a7c6-a88670595ce8@linux.dev>
Date: Sun, 14 Dec 2025 06:26:03 +0900
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 "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.org>
Cc: Shuah Khan <shuah@...nel.org>, Ido Schimmel <idosch@...dia.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCH net 2/2] selftests: fib_nexthops: Add test case for ipv4
 multi nexthops

On 13/12/2025 21:18, Willem de Bruijn wrote:
> 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 .. ]

Got it.

> 
>>
>> 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?

Sounds reasonable, I'll split it in v2

> 
>> +{
>> +	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?

Ah, yeah, looks like a leftover from previous version, thanks for
catching!

>> +	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
>>
> 
>