netdev - Re: [PATCH net v2 2/2] selftests: fib_test: Add test case for ipv4 multi nexthops

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Message-ID: <willemdebruijn.kernel.14a486c1824f2@gmail.com>
Date: Sun, 21 Dec 2025 10:59:18 -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.org>
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 v2 2/2] selftests: fib_test: 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 dummy
> interface, it checks that the routes are balanced.
> 
> Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>

> ---
> v1 -> v2:
> - move tests to fib_tests.sh
> ---
>  tools/testing/selftests/net/fib_tests.sh | 70 +++++++++++++++++++++++-
>  1 file changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/net/fib_tests.sh b/tools/testing/selftests/net/fib_tests.sh
> index a88f797c549a..c5694cc4ddd2 100755
> --- a/tools/testing/selftests/net/fib_tests.sh
> +++ b/tools/testing/selftests/net/fib_tests.sh
> @@ -12,7 +12,7 @@ TESTS="unregister down carrier nexthop suppress ipv6_notify ipv4_notify \
>         ipv4_route_metrics ipv4_route_v6_gw rp_filter ipv4_del_addr \
>         ipv6_del_addr ipv4_mangle ipv6_mangle ipv4_bcast_neigh fib6_gc_test \
>         ipv4_mpath_list ipv6_mpath_list ipv4_mpath_balance ipv6_mpath_balance \
> -       fib6_ra_to_static"
> +       ipv4_mpath_balance_preferred fib6_ra_to_static"
>  
>  VERBOSE=0
>  PAUSE_ON_FAIL=no
> @@ -2751,6 +2751,73 @@ ipv4_mpath_balance_test()
>  	forwarding_cleanup
>  }
>  
> +get_route_dev_src()
> +{
> +	local pfx="$1"
> +	local src="$2"

only with my highly pedantic hat on, and only if respinning: these can be local -r

> +	local out
> +
> +	if out=$($IP -j route get "$pfx" from "$src" | jq -re ".[0].dev"); then
> +		echo "$out"
> +	fi
> +}
> +
> +ipv4_mpath_preferred()
> +{
> +	local src_ip=$1
> +	local pref_dev=$2
> +	local dev routes
> +	local route0=0
> +	local route1=0
> +	local pref_route=0
> +	num_routes=254
> +
> +	for i in $(seq 1 $num_routes) ; do
> +		dev=$(get_route_dev_src 172.16.105.$i $src_ip)

Similarly, I was going to ask to avoid open coding the ip prefixes
repeatedly. But that is the style in this file, so fine to follow.

> +		if [ "$dev" = "$pref_dev" ]; then
> +			pref_route=$((pref_route+1))
> +		elif [ "$dev" = "veth1" ]; then
> +			route0=$((route0+1))
> +		elif [ "$dev" = "veth3" ]; then
> +			route1=$((route1+1))
> +		fi
> +	done
> +
> +	routes=$((route0+route1))
> +
> +	[ "$VERBOSE" = "1" ] && echo "multipath: routes seen: ($route0,$route1,$pref_route)"
> +
> +	if [ x"$pref_dev" = x"" ]; then
> +		[[ $routes -ge $num_routes ]] && [[ $route0 -gt 0 ]] && [[ $route1 -gt 0 ]]
> +	else
> +		[[ $pref_route -ge $num_routes ]]
> +	fi
> +
> +}
> +
> +ipv4_mpath_balance_preferred_test()
> +{
> +	echo
> +	echo "IPv4 multipath load balance preferred route"
> +
> +	forwarding_setup
> +
> +	$IP route add 172.16.105.0/24 \
> +		nexthop via 172.16.101.2 \
> +		nexthop via 172.16.103.2
> +
> +	ipv4_mpath_preferred 172.16.101.1 veth1
> +	log_test $? 0 "IPv4 multipath loadbalance from veth1"
> +
> +	ipv4_mpath_preferred 172.16.103.1 veth3
> +	log_test $? 0 "IPv4 multipath loadbalance from veth3"
> +
> +	ipv4_mpath_preferred 198.51.100.1
> +	log_test $? 0 "IPv4 multipath loadbalance from dummy"
> +
> +	forwarding_cleanup
> +}
> +
>  ipv6_mpath_balance_test()
>  {
>  	echo
> @@ -2861,6 +2928,7 @@ do
>  	ipv6_mpath_list)		ipv6_mpath_list_test;;
>  	ipv4_mpath_balance)		ipv4_mpath_balance_test;;
>  	ipv6_mpath_balance)		ipv6_mpath_balance_test;;
> +	ipv4_mpath_balance_preferred)	ipv4_mpath_balance_preferred_test;;
>  	fib6_ra_to_static)		fib6_ra_to_static;;
>  
>  	help) echo "Test names: $TESTS"; exit 0;;
> -- 
> 2.47.3
>