From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Oliver Herms <oliver.peter.herms@gmail.com>,
netdev@vger.kernel.org, davem@davemloft.net,
kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org
Subject: Re: [PATCH v3] IPv4: Tunnel: Fix effective path mtu calculation
Date: Wed, 1 Jul 2020 00:27:34 +0200 [thread overview]
Message-ID: <86c71cc0-462c-2365-00ea-7f9e79c204b7@6wind.com> (raw)
In-Reply-To: <20200630103335.63de7098@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Le 30/06/2020 à 19:33, Jakub Kicinski a écrit :
> On Tue, 30 Jun 2020 17:51:41 +0200 Nicolas Dichtel wrote:
>> Le 30/06/2020 à 08:22, Jakub Kicinski a écrit :
>> [snip]
>>> My understanding is that for a while now tunnels are not supposed to use
>>> dev->hard_header_len to reserve skb space, and use dev->needed_headroom,
>>> instead. sit uses hard_header_len and doesn't even copy needed_headroom
>>> of the lower device.
>>
>> I missed this. I was wondering why IPv6 tunnels uses hard_header_len, if there
>> was a "good" reason:
>>
>> $ git grep "hard_header_len.*=" net/ipv6/
>> net/ipv6/ip6_tunnel.c: dev->hard_header_len =
>> tdev->hard_header_len + t_hlen;
>> net/ipv6/ip6_tunnel.c: dev->hard_header_len = LL_MAX_HEADER + t_hlen;
>> net/ipv6/sit.c: dev->hard_header_len = tdev->hard_header_len +
>> sizeof(struct iphdr);
>> net/ipv6/sit.c: dev->hard_header_len = LL_MAX_HEADER + t_hlen;
>>
>> A cleanup would be nice ;-)
>
> I did some archaeological investigatin' yesterday, and I saw
> c95b819ad75b ("gre: Use needed_headroom") which converted GRE.
Thanks for the pointer.
> Then I think Pravin used GRE as a base for better ip_tunnel infra
> and the no-hard_header_len-abuse gospel has spread to other IPv4
> tunnels. AFAICT IPv6 tunnels were not as lucky, and SIT just got
> missed in the IPV4 conversion..
Yep, I agree with you, it's probably "historical".
prev parent reply other threads:[~2020-06-30 22:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-25 22:44 [PATCH v3] IPv4: Tunnel: Fix effective path mtu calculation Oliver Herms
2020-06-30 6:22 ` Jakub Kicinski
2020-06-30 10:21 ` Oliver Herms
2020-06-30 17:27 ` Jakub Kicinski
2020-06-30 15:51 ` Nicolas Dichtel
2020-06-30 17:33 ` Jakub Kicinski
2020-06-30 22:27 ` Nicolas Dichtel [this message]
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