netdev - how to search for the best route from userspace in netlink?

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Message-ID: <CAA93jw73AJMwLL+6cNLB2R6oqA2DyMYc1ZUsrFPndESs0ZONng@mail.gmail.com>
Date:   Mon, 2 Sep 2019 15:07:31 -0700
From:   Dave Taht <dave.taht@...il.com>
To:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: how to search for the best route from userspace in netlink?

Windows has the "RtmGetMostSpecificDestination" call:
https://docs.microsoft.com/en-us/windows/win32/rras/search-for-the-best-route

In particular, I wanted to search for the best route, AND pick up the
PMTU from that (if it existed)
for older UDP applications like dnssec[1] and newer ones like QUIC[2].
The alternatives, which
basically include probing perpetually and/or picking really low
values, seem increasingly less than
optimal.

Put in a wrapper around bpf[3]'s lpm calls? Create a new netlink message?

[1] https://github.com/dns-violations/dnsflagday/issues/125
[2] https://tools.ietf.org/html/draft-ietf-quic-transport-22#section-14.1
[3] https://github.com/torvalds/linux/blob/master/kernel/bpf/lpm_trie.c#L164

-- 

Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-205-9740