Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] net: ipv6: don't generate link-local address in any
 addr_gen_mode
To:     Lorenzo Colitti <lorenzo@google.com>
Cc:     Rocco Yue <rocco.yue@mediatek.com>,
        "David S . Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Linux NetDev <netdev@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
        rocco.yue@gmail.com, chao.song@mediatek.com,
        =?UTF-8?B?S3VvaG9uZyBXYW5nICjnjovlnIvptLsp?= 
        <kuohong.wang@mediatek.com>,
        =?UTF-8?B?Wmh1b2xpYW5nIFpoYW5nICjlvKDljZPkuq4p?= 
        <zhuoliang.zhang@mediatek.com>
References: <46a9dbf2-9748-330a-963e-57e615a15440@gmail.com>
 <20210701085117.19018-1-rocco.yue@mediatek.com>
 <62c9f5b7-84bd-d809-4e33-39fed7a9d780@gmail.com>
 <CAKD1Yr2aijPe_aq+SRm-xv0ZPoz_gKjYrEX97R1NJyYpSnv4zg@mail.gmail.com>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <6a8f0e91-225a-e2a8-3745-12ff1710a8df@gmail.com>
Date:   Thu, 9 Sep 2021 13:12:37 -0600
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0)
 Gecko/20100101 Thunderbird/78.14.0
MIME-Version: 1.0
In-Reply-To: <CAKD1Yr2aijPe_aq+SRm-xv0ZPoz_gKjYrEX97R1NJyYpSnv4zg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 9/9/21 12:20 AM, Lorenzo Colitti wrote:
>> I think another addr_gen_mode is better than a separate sysctl. It looks
>> like IN6_ADDR_GEN_MODE_STABLE_PRIVACY and IN6_ADDR_GEN_MODE_RANDOM are
>> the ones used for RAs, so add something like:
>>
>> IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
>> IN6_ADDR_GEN_MODE_RANDOM_NO_LLA,
> 
> I think the real requirement here (which wasn't clear in this thread)
> is that the network needs to control the interface ID (i.e., the
> bottom 64 bits) of the link-local address, but the device is free to
> use whatever interface IDs to form global addresses. See:
> https://www.etsi.org/deliver/etsi_ts/129000_129099/129061/15.03.00_60/ts_129061v150300p.pdf
> 
> How do you think that would best be implemented?

There is an established paradigm for configuring how an IPv6 address is
created or whether it is created at all - the IFLA_INET6_ADDR_GEN_MODE
attribute.

> 
> 1. The actual interface ID could be passed in using IFLA_INET6_TOKEN,
> but there is only one token, so that would cause all future addresses
> to use the token, disabling things like privacy addresses (bad).
> 2. We could add new IN6_ADDR_GEN_MODE_STABLE_PRIVACY_LL_TOKEN,
> IN6_ADDR_GEN_MODE_RANDOM_LL_TOKEN, etc., but we'd need to add one such
> mode for every new mode we add.
> 3. We could add a separate sysctl for the link-local address, but you
> said that per-device sysctls aren't free.

per-device sysctl's are one of primary causes of per netdev memory usage.

Besides that there is no reason to add complexity by having a link
attribute and a sysctl for this feature.

> 4. We could change the behaviour so that if the user configures a
> token and then sets IN6_ADDR_GEN_MODE_*, then we use the token only
> for the link-local address. But that would impact backwards
> compatibility.
> 
> Thoughts?

We can have up to 255 ADDR_GEN_MODEs (GEN_MODE is a u8). There is
established code for handling the attribute and changes to it. Let's
reuse it.