From: Mateusz Bajorski <redacted>
Date: Wed, 29 Jun 2016 09:22:10 +0200

When adding rule with NLM_F_EXCL flag then check if the same rule exist.
If yes then exit with -EEXIST.

This is already implemented in iproute2:
        if (cmd == RTM_NEWRULE) {
                req.n.nlmsg_flags |= NLM_F_CREATE|NLM_F_EXCL;
                req.r.rtm_type = RTN_UNICAST;
        }

Tested ipv4 and ipv6 with net-next linux on qemu x86

expected behavior after patch:
localhost ~ # ip rule
0:    from all lookup local
32766:    from all lookup main
32767:    from all lookup default
localhost ~ # ip rule add from 10.46.177.97 lookup 104 pref 1005
localhost ~ # ip rule add from 10.46.177.97 lookup 104 pref 1005
RTNETLINK answers: File exists
localhost ~ # ip rule
0:    from all lookup local
1005:    from 10.46.177.97 lookup 104
32766:    from all lookup main
32767:    from all lookup default

There was already topic regarding this but I don't see any changes
merged and problem still occurs.
https://lkml.kernel.org/r/1135778809.5944.7.camel+%28%29+localhost+%21+localdomain

Signed-off-by: Mateusz Bajorski <redacted>

Applied to net-next, thanks.