netdev - Re: Question about linux kernel commit: "net/ipv6: move metrics from dst to rt6

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Message-ID: <5981b8d0-cfdf-d230-fa22-cfcfaa5ee4b9@gmail.com>
Date:   Wed, 10 Jul 2019 13:13:03 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stefano Brivio <sbrivio@...hat.com>,
        Jan Szewczyk <jan.szewczyk@...csson.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Wei Wang <weiwan@...gle.com>, Martin KaFai Lau <kafai@...com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: Question about linux kernel commit: "net/ipv6: move metrics from
 dst to rt6_info"

On 7/10/19 1:09 PM, Stefano Brivio wrote:
> Jan,
> 
> On Wed, 10 Jul 2019 12:59:41 +0000
> Jan Szewczyk <jan.szewczyk@...csson.com> wrote:
> 
>> Hi!
>> I digged up a little further and maybe it's not a problem with MTU
>> itself. I checked every entry I get from RTM_GETROUTE netlink message
>> and after triggering "too big packet" by pinging ipv6address I get
>> exactly the same messages on 4.12 and 4.18, except that the one with
>> that pinged ipv6address is missing on 4.18 at all. What is weird -
>> it's visible when running "ip route get to ipv6address". Do you know
>> why there is a mismatch there?
> 
> If I understand you correctly, an implementation equivalent to 'ip -6
> route list show' (using the NLM_F_DUMP flag) won't show the so-called
> route exception, while 'ip -6 route get' shows it.
> 
> If that's the case: that was broken by commit 2b760fcf5cfb ("ipv6: hook
> up exception table to store dst cache") that landed in 4.15, and fixed
> by net-next commit 1e47b4837f3b ("ipv6: Dump route exceptions if
> requested"). For more details, see the log of this commit itself.
> 

ah, good point. My mind locked on RTM_GETROUTE as a specific route
request not a dump.