netdev - Re: [PATCH net 2/2] net: dsa: tag_8021q: Create a stable binary format

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Message-ID: <CA+h21hoD21GCbSS7R0Av3tRe7LoxqRSmmNnCTrQZVCjQYCiGPw@mail.gmail.com>
Date:   Wed, 29 May 2019 13:09:50 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Ioana Ciornei <ioana.ciornei@....com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 2/2] net: dsa: tag_8021q: Create a stable binary format

On Wed, 29 May 2019 at 04:08, Florian Fainelli <f.fainelli@...il.com> wrote:
>
>
>
> On 5/28/2019 3:50 PM, Vladimir Oltean wrote:
> > Tools like tcpdump need to be able to decode the significance of fake
> > VLAN headers that DSA uses to separate switch ports.
> >
> > But currently these have no global significance - they are simply an
> > ordered list of DSA_MAX_SWITCHES x DSA_MAX_PORTS numbers ending at 4095.
> >
> > The reason why this is submitted as a fix is that the existing mapping
> > of VIDs should not enter into a stable kernel, so we can pretend that
> > only the new format exists. This way tcpdump won't need to try to make
> > something out of the VLAN tags on 5.2 kernels.
> >
> > Fixes: f9bbe4477c30 ("net: dsa: Optional VLAN-based port separation for switches without tagging")
> > Signed-off-by: Vladimir Oltean <olteanv@...il.com>
>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
>
> This looks a lot nicer actually, and kudos for documenting the format.
> --
> Florian

Please don't merge this. The MBZ bit doesn't actually prevent the VID
from taking the reserved value of 0. I don't know what I was thinking.
I'll send out a v2 soon.

Thanks,
-Vladimir