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Date: Tue, 23 May 2023 13:29:51 -0700
From: Jakub Kicinski <kuba@kernel.org>
Message-ID: <20230523132951.623288cb@kernel.org>
In-Reply-To: <ZGx0/hwPmFFN2ivS@shredder>
References: <20230518113328.1952135-1-idosch@nvidia.com>
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Subject: Re: [Bridge] [PATCH net-next 1/5] skbuff: bridge: Add layer 2 miss
 indication
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To: Ido Schimmel <idosch@nvidia.com>
Cc: taras.chornyi@plvision.eu, petrm@nvidia.com, alexandre.belloni@bootlin.com, jiri@resnulli.us, taspelund@nvidia.com, leon@kernel.org, netdev@vger.kernel.org, razor@blackwall.org, bridge@lists.linux-foundation.org, claudiu.manoil@nxp.com, UNGLinuxDriver@microchip.com, vladimir.oltean@nxp.com, edumazet@google.com, jhs@mojatatu.com, roopa@nvidia.com, xiyou.wangcong@gmail.com, pabeni@redhat.com, saeedm@nvidia.com, davem@davemloft.net

On Tue, 23 May 2023 11:10:38 +0300 Ido Schimmel wrote:
> > Can we possibly put the new field at the end of the CB and then have TC
> > look at it in the CB? We already do a bit of such CB juggling in strp
> > (first member of struct sk_skb_cb).  
> 
> Using the CB between different layers is very fragile and I would like
> to avoid it. Note that the skb can pass various layers until hitting the
> classifier, each of which can decide to memset() the CB.
> 
> Anyway, I think I have a better alternative. I added the 'l2_miss' bit
> to the tc skb extension and adjusted the bridge to mark packets via this
> extension. The entire thing is protected by the existing 'tc_skb_ext_tc'
> static key, so overhead is kept to a minimum when feature is disabled.
> Extended flower to enable / disable this key when filters that match on
> 'l2_miss' are added / removed.
> 
> bridge change to mark the packet:
> https://github.com/idosch/linux/commit/3fab206492fcad9177f2340680f02ced1b9a0dec.patch
> 
> flow_dissector change to dissect the info from the extension:
> https://github.com/idosch/linux/commit/1533c078b02586547817a4e63989a0db62aa5315.patch
> 
> flower change to enable / disable the key:
> https://github.com/idosch/linux/commit/cf84b277511ec80fe565c41271abc6b2e2f629af.patch
> 
> Advantages compared to the previous approach are that we do not need a
> new bit in the skb and that overhead is kept to a minimum when feature
> is disabled. Disadvantage is that overhead is higher when feature is
> enabled.
> 
> WDYT?

Sounds good, yup. Thanks!