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([2a01:e0a:410:bb00:69db:fab1:ccba:51cb]) by smtp.gmail.com with ESMTPSA id t13sm2111291wrw.19.2020.02.13.01.34.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2020 01:34:20 -0800 (PST) Reply-To: nicolas.dichtel@6wind.com Subject: Re: [PATCH v3 net] net, ip6_tunnel: enhance tunnel locate with link check To: William Dauchy Cc: netdev@vger.kernel.org References: <20200212083036.134761-1-w.dauchy@criteo.com> <20200212210647.GB159357@dontpanic> From: Nicolas Dichtel Organization: 6WIND Message-ID: Date: Thu, 13 Feb 2020 10:34:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200212210647.GB159357@dontpanic> 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 12/02/2020 à 22:06, William Dauchy a écrit : > Hello Nicolas, > > Thank you for your review. > > On Wed, Feb 12, 2020 at 04:54:19PM +0100, Nicolas Dichtel wrote: >> Hmm, I was expecting 'tdev->mtu - t_hlen'. Am I wrong? >> >> In fact, something like this: >> dev->mtu = ETH_DATA_LEN - t_hlen; >> if (t->parms.link) { >> tdev = __dev_get_by_index(t->net, t->parms.link); >> if (tdev) >> dev->mtu = tdev->mtu - t_hlen; >> } > > true, I missed that one; I reworked to something like: > > int mtu; > > mtu = ETH_DATA_LEN; > if (t->parms.link) { > tdev = __dev_get_by_index(t->net, t->parms.link); > if (tdev && tdev->mtu < mtu) Why this second condition? Why not allowing more than ETH_DATA_LEN (1500)? ip_tunnels do: if (tdev) { hlen = tdev->hard_header_len + tdev->needed_headroom; mtu = min(tdev->mtu, IP_MAX_MTU); } which seems better. Note also that you patch ip6_tnl_dev_init_gen(), but ip6_tnl_link_config() is called later and may adjust the mtu. I would suggest to take care of link mtu in ip6_tnl_link_config(). > mtu = tdev->mtu; > } > dev->mtu = mtu - t_hlen; > > > However in ipip we do: > > mtu -= (dev->hard_header_len + t_hlen); > > Do I need to use hard_header_len as well? hard_header_len is not set for ipv4 tunnels, but for ipv6 tunnels: dev->hard_header_len = LL_MAX_HEADER + t_hlen; This is not the real value, I don't think you can calculate the real mtu based on this. Regards, Nicolas