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([2a01:e0a:410:bb00:981f:ef60:cbba:acb2]) by smtp.gmail.com with ESMTPSA id d18sm4432294wrj.8.2020.06.30.08.51.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Jun 2020 08:51:42 -0700 (PDT) Reply-To: nicolas.dichtel@6wind.com Subject: Re: [PATCH v3] IPv4: Tunnel: Fix effective path mtu calculation To: Jakub Kicinski , Oliver Herms Cc: netdev@vger.kernel.org, davem@davemloft.net, kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org References: <20200625224435.GA2325089@tws> <20200629232235.6047a9c1@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Nicolas Dichtel Organization: 6WIND Message-ID: <99564f5c-07e4-df0d-893d-40757a0f2167@6wind.com> Date: Tue, 30 Jun 2020 17:51:41 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200629232235.6047a9c1@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 ;-)