linux-kernel - Q: (rt)netlink documentation

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Message-Id: <62A2EB9C020000A10004ACB6@gwsmtp.uni-regensburg.de>
Date:   Fri, 10 Jun 2022 08:58:36 +0200
From:   "Ulrich Windl" <Ulrich.Windl@...uni-regensburg.de>
To:     <linux-kernel@...r.kernel.org>
Subject: Q: (rt)netlink documentation

Hi!

I'm working with an older kernel (SLES12 SP5, 4.12.14), trying to implement a module to access rtnetlink data, specifically that returned for RTM_GETLINK.
However I have the problem that the documentation on the packet structure is very poor, if not to say absent. So I fail to parse the response correctly.
Furthermore I realized (when trying to contact the maintainer), that "netlink" is not present in the MAINTAINERS file.

To be honest, the only working example I have is derived from some C code someone had published.
>From the manual pages or header files (even from the kernel sources, or the Documentation directory) it's absolutely non-obvious how the data is structured and how to use those many macros defined.

NLMSG_ALIGN
RTA_ALIGN
RTA_OK
RTA_NEXT
RTA_LENGTH
RTA_SPACE
RTA_DATA
RTA_PAYLOAD
RTM_RTA
RTM_PAYLOAD
TCA_RTA
TCA_PAYLOAD
TA_RTA
TA_PAYLOAD
NFDN_RTMSG
NLMSG_LENGTH
NLMSG_SPACE
NLMSG_DATA
NLMSG_NEXT
NLMSG_OK
NLMSG_PAYLOAD
IFA_RTA
IFA_PAYLOAD
NFM_PAYLOAD
IFLA_RTA
IFLA_PAYLOAD
(This list is most likely not complete)

Regards,
Ulrich Windl
P.S.: Keep me on CC:, I'm not subscribed to LKML