netdev - Re: [PATCH v2] net: core: SIOCADDMULTI/SIOCDELMULTI distinguish between uc and mc

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Message-ID: <1598452669073.46639@cisco.com>
Date:   Wed, 26 Aug 2020 14:37:49 +0000
From:   "Denys Zagorui -X (dzagorui - GLOBALLOGIC INC at Cisco)" 
        <dzagorui@...co.com>
To:     David Miller <davem@...emloft.net>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net: core: SIOCADDMULTI/SIOCDELMULTI distinguish
 between uc and mc

>This doesn't seem appropriate at all.  If anything UC addresses
>should be blocked and the Intel driver change reverted.  We have
>a well defined way to add secondary UC addresses and the MC interfaces
>are not it.

As I understand by ‘well defined way’ you mean macvlan feature. But macvlan 
is more virtualisation thing where an additional netdevice is created and for each
skb passed to linux stack hash_lookup is made to find a netdevice to which this
skb belongs to based on mac_dst. In case if someone want to have a network
protocol on top of physical layer (AF_PACKET) where NIC should allow several uc
mac addr without enabling promiscuous mode i am not sure that for this simple
task macvlan is needed.

>Furthermore, even if this was appropriate, "fixing" this only for
>ethernet is definitely not appropriate.  The fix would need to be able
>to handle any address type.  Having a generic interface work
>inconsistently for one link type vs. another is a non-starter.

Maybe overusing multicast api isn’t the best choice for this purpose, but i noticed
that it is already overused by i40 for the same purpose, that is why i suggested
this diff. Anyway i can add separate ioctls for add/del secondary uc, if this is worth it.