selftests/net: convert fib_nexthop_multiprefix to run it in unique namespace

Here is the test result after conversion.

]# ./fib_nexthop_multiprefix.sh
TEST: IPv4: host 0 to host 1, mtu 1300 [ OK ]
TEST: IPv6: host 0 to host 1, mtu 1300 [ OK ]

TEST: IPv4: host 0 to host 2, mtu 1350 [ OK ]
TEST: IPv6: host 0 to host 2, mtu 1350 [ OK ]

TEST: IPv4: host 0 to host 3, mtu 1400 [ OK ]
TEST: IPv6: host 0 to host 3, mtu 1400 [ OK ]

TEST: IPv4: host 0 to host 1, mtu 1300 [ OK ]
TEST: IPv6: host 0 to host 1, mtu 1300 [ OK ]

TEST: IPv4: host 0 to host 2, mtu 1350 [ OK ]
TEST: IPv6: host 0 to host 2, mtu 1350 [ OK ]

TEST: IPv4: host 0 to host 3, mtu 1400 [ OK ]
TEST: IPv6: host 0 to host 3, mtu 1400 [ OK ]

Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20231213060856.4030084-8-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests/net: fix grep checking for fib_nexthop_multiprefix

When running fib_nexthop_multiprefix test I saw all IPv6 test failed.
e.g.

]# ./fib_nexthop_multiprefix.sh
TEST: IPv4: host 0 to host 1, mtu 1300 [ OK ]
TEST: IPv6: host 0 to host 1, mtu 1300 [FAIL]

With -v it shows

COMMAND: ip netns exec h0 /usr/sbin/ping6 -s 1350 -c5 -w5 2001:db8:101::1
PING 2001:db8:101::1(2001:db8:101::1) 1350 data bytes
From 2001:db8:100::64 icmp_seq=1 Packet too big: mtu=1300

--- 2001:db8:101::1 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

Route get
2001:db8:101::1 via 2001:db8:100::64 dev eth0 src 2001:db8:100::1 metric 1024 expires 599sec mtu 1300 pref medium
Searching for:
2001:db8:101::1 from :: via 2001:db8:100::64 dev eth0 src 2001:db8:100::1 .* mtu 1300

The reason is when CONFIG_IPV6_SUBTREES is not enabled, rt6_fill_node() will
not put RTA_SRC info. After fix:

]# ./fib_nexthop_multiprefix.sh
TEST: IPv4: host 0 to host 1, mtu 1300 [ OK ]
TEST: IPv6: host 0 to host 1, mtu 1300 [ OK ]

Fixes: 735ab2f65dce ("selftests: Add test with multiple prefixes using single nexthop")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20231213060856.4030084-7-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests: fib_nexthop_multiprefix: fix cleanup() netns deletion

During setup():
...
for ns in h0 r1 h1 h2 h3
do
create_ns ${ns}
done
...

while in cleanup():
...
for n in h1 r1 h2 h3 h4
do
ip netns del ${n} 2>/dev/null
done
...

and after removing the stderr redirection in cleanup():

$ sudo ./fib_nexthop_multiprefix.sh
...
TEST: IPv4: host 0 to host 3, mtu 1400 [ OK ]
TEST: IPv6: host 0 to host 3, mtu 1400 [ OK ]
Cannot remove namespace file "/run/netns/h4": No such file or directory
$ echo $?
1

and a non-zero return code, make kselftests fail (even if the test
itself is fine):

...
not ok 34 selftests: net: fib_nexthop_multiprefix.sh # exit=1
...

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: Update fib_nexthop_multiprefix to handle missing ping6

Some distributions (e.g., debian buster) do not install ping6. Re-use
the hook in pmtu.sh to detect this and fallback to ping.

Fixes: 735ab2f65dce ("selftests: Add test with multiple prefixes using single nexthop")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

selftests: Add test with multiple prefixes using single nexthop

Add tests where multiple FIB entries use the same nexthop object. Generate
per-cpu cached routes for each by running ping on each cpu, and then
generate exceptions unique to each prefix (remote host) with different
mtus.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>