netdev - Re: gateway field missing in netlink message

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Date:   Mon, 9 May 2022 06:59:05 +0000
From:   "Magesh  M P" <magesh@...itizethings.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     David Ahern <dsahern@...il.com>
Subject: Re: gateway field missing in netlink message

Hi Steve/Dave,

Thank you very much for great support and sharing the knowledge.

Dave referred me the file iproute.c but this contains the flow from user space to kernel.

In my problematic scenario, the use case is from Linux kernel to VPP kernel and this is where my parser at vpp kernel is not doing its work properly. The VPP stack tries to synchronize the routing table information from Linux kernel through netlink messages.

My file netns.c looks like the following:
vpp-netlink/netns.c at master · Oryon/vpp-netlink · GitHub

I tried to implement the parser logic as shown in the following link but that did not help.
Parsing the RTA_MULTIPATH attribute from Rtnetlink | Eder L. Fernandes (ederlf.website)

I see only one gateway in parsing the RTA_MULTIPATH attribute inspite when I had configured dual gateways.

The existing code in netns.c works fine for single gateway ip route configuration and it fails in dual gateway ECMP case. 

Your help is greatly appreciated.

Best regards
Magesh

Sent from Mail for Windows

From: Stephen Hemminger
Sent: 05 May 2022 21:58
To: Magesh M P
Cc: David Ahern
Subject: Re: gateway field missing in netlink message

Have you considered using libmnl it is good way to handle the
low level parts of netlink parsing.

https://www.netfilter.org/projects/libmnl/