netdev - Re: [PATCH net] net: lan78xx: Disable hardware vlan filtering in promiscuous mode

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Message-ID: <20201112164457.6af0fbaf@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 12 Nov 2020 16:44:57 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Markus Blöchl <markus.bloechl@...tronik.com>,
        Ido Schimmel <idosch@...sch.org>, Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <olteanv@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net] net: lan78xx: Disable hardware vlan filtering in
 promiscuous mode

On Wed, 11 Nov 2020 07:43:41 -0800 Jakub Kicinski wrote:
> >     In order to receive those tagged frames it is necessary to manually disable
> >     rx vlan filtering using ethtool ( `ethtool -K ethX rx-vlan-filter off` or
> >     corresponding ioctls ). Setting all bits in the vlan filter table to 1 is
> >     an even worse approach, imho.
> > 
> >     As a user I would probably expect that setting IFF_PROMISC should be enough
> >     in all cases to receive all valid traffic.
> >     Therefore I think this behaviour is a bug in the driver, since other
> >     drivers (notably ixgbe) automatically disable rx-vlan-filter when
> >     IFF_PROMISC is set. Please correct me if I am wrong here.  
> 
> I've been mulling over this, I'm not 100% sure that disabling VLAN
> filters on promisc is indeed the right thing to do. The ixgbe doing
> this is somewhat convincing. OTOH users would not expect flow filters
> to get disabled when promisc is on, so why disable vlan filters?
> 
> Either way we should either document this as an expected behavior or
> make the core clear the features automatically rather than force
> drivers to worry about it.
> 
> Does anyone else have an opinion, please?

Okay, I feel convinced that we should indeed let all vlan traffic thru,
thanks everyone! :)

Markus could you try to come up with a patch for the net/core/dev.c
handling which would clear NETIF_F_HW_VLAN_CTAG_FILTER and
NETIF_F_HW_VLAN_STAG_FILTER automatically so the drivers don't have 
to worry?

Whatever the driver chooses to do to disable vlan filtering is a
separate discussion AFAICT.