netdev - Re: [PATCH iproute2-next] bridge: fdb: Use 'struct ndmsg' for FDB dumping

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Date:   Mon, 31 Dec 2018 20:25:38 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     David Ahern <dsahern@...il.com>
Cc:     Ido Schimmel <idosch@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH iproute2-next] bridge: fdb: Use 'struct ndmsg' for FDB
 dumping

On Sun, 30 Dec 2018 18:03:47 -0700
David Ahern <dsahern@...il.com> wrote:

> On 12/30/18 10:14 AM, Ido Schimmel wrote:
> > Since commit aea41afcfd6d ("ip bridge: Set NETLINK_GET_STRICT_CHK on
> > socket") iproute2 uses strict checking on kernels that support it. This
> > causes FDB dumping to fail [1], as iproute2 uses 'struct ifinfomsg'
> > whereas the kernel expects 'struct ndmsg'.
> > 
> > Note that with this change iproute2 continues to work on old kernels
> > that do not support strict checking, but contain the fix introduced in
> > kernel commit bd961c9bc664 ("rtnetlink: fix rtnl_fdb_dump() for ndmsg
> > header").

Sorry, I don't think that is good enough backward compatibility guarantee.
Iproute2 should work on really old kernels like 2.6.32. If not then then iproute2
utility is broken or the changes to the kernel API were incorrect.

You can't depend on some old commit.