linux-kernel - Re: [PATCH 1/4] net: if_arp: add ARPHRD

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Date:   Thu, 24 Jun 2021 20:24:35 +0800
From:   Rocco Yue <rocco.yue@...iatek.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>, <netdev@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <bpf@...r.kernel.org>,
        <wsd_upstream@...iatek.com>, <chao.song@...iatek.com>,
        <kuohong.wang@...iatek.com>, Rocco Yue <rocco.yue@...iatek.com>
Subject: Re: [PATCH 1/4] net: if_arp: add ARPHRD_PUREIP type

On Thu, 2021-06-24 at 11:04 +0200, Greg KH wrote:
On Thu, Jun 24, 2021 at 02:13:10PM +0800, Rocco Yue wrote:
>> On Thu, 2021-06-24 at 07:29 +0200, Greg KH wrote:
>>> 
>>> Thanks for the explaination, why is this hardware somehow "special" in
>>> this way that this has never been needed before?
>>> 
>>> thanks,
>>> 
>>> greg k-h
>>> 
>> 
>> Before kernel-4.18, RAWIP was the same as PUREIP, neither of them
>> automatically generates an IPv6 link-local address, and the way to
>> generate an IPv6 global address is the same.
>> 
>> After kernel-4.18 (include 4.18 version), the behavior of RAWIP had
>> changed due to the following patch:
>> @@  static int ipv6_generate_eui64(u8 *eui, struct net_device *dev)
>> +	case ARPHRD_RAWIP:
>> +		return addrconf_ifid_rawip(eui, dev);
>>  	}
>>  	return -1;
>> }
>> 
>> the reason why the kernel doesn't need to generate the link-local
>> address automatically is as follows:
>> 
>> In the 3GPP 29.061, here is some description as follows:
>> "in order to avoid any conflict between the link-local address of
>> MS and that of the GGSN, the Interface-Identifier used by the MS to
>> build its link-local address shall be assigned by the GGSN. The GGSN
>> ensures the uniqueness of this Interface-Identifier. Then MT shall
>> then enforce the use of this Interface-Identifier by the TE"
>> 
>> In other words, in the cellular network, GGSN determines whether to
>> reply to the Router Solicitation message of UE by identifying the
>> low 64bits of UE interface's ipv6 link-local address.
>> 
>> When using a new kernel and RAWIP, kernel will generate an EUI64
>> format ipv6 link-local address, and if the device uses this address
>> to send RS, GGSN will not reply RA message.
>> 
>> Therefore, in that background, we came up with PUREIP to make kernel
>> doesn't generate a ipv6 link-local address in any address generate
>> mode.
> 
> Thanks for the better description.  That should go into the changelog
> text somewhere so that others know what is going on here with this new
> option.
>

Does changelog mean adding these details to the commit message ?
I am willing do it.

> And are these user-visable flags documented in a man page or something
> else somewhere?  If not, how does userspace know about them?
> 

There are mappings of these device types value in the libc:
"/bionic/libc/kernel/uapi/linux/if_arp.h".
userspace can get it from here.

But I also failed to find a man page or a description of these
device types.

Thanks,
Rocco