netdev - Re: [PATCH 3/6] [NET] dsa: add support for original DSA tagging format

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Date:	Fri, 03 Oct 2008 18:25:59 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Lennert Buytenhek <buytenh@...tstofly.org>
Cc:	netdev@...r.kernel.org, Byron Bradley <byron.bbradley@...il.com>,
	Jesper Dangaard Brouer <jdb@...x.dk>,
	Tim Ellis <tim.ellis@....com>,
	Andy Fleming <afleming@...escale.com>,
	Imre Kaloz <kaloz@...nwrt.org>, Nicolas Pitre <nico@....org>,
	Dirk Teurlings <dirk@...xia.nl>,
	Peter van Valderen <p.v.valderen@...il.com>
Subject: Re: [PATCH 3/6] [NET] dsa: add support for original DSA tagging
	format

On Mon, 2008-09-29 at 04:38 +0200, Lennert Buytenhek wrote:
> Most of the DSA switches currently in the field do not support the
> Ethertype DSA tagging format that one of the previous patches added
> support for, but only the original DSA tagging format.
> 
> The original DSA tagging format carries the same information as the
> Ethertype DSA tagging format, but with the difference that it does not
> have an ethertype field.  In other words, when receiving a packet that
> is tagged with an original DSA tag, there is no way of telling in
> eth_type_trans() that this packet is in fact a DSA-tagged packet.
> 
> This patch adds a hook into eth_type_trans() which is only compiled in
> if support for a switch chip that doesn't support Ethertype DSA is
> selected, and which checks whether there is a DSA switch driver
> instance attached to this network device which uses the old tag format.
> If so, it sets the protocol field to ETH_P_DSA without looking at the
> packet, so that the packet ends up in the right place.
[...]

Why should this go in eth_type_trans()?  Why don't you put the hook into
the specific network driver(s) that need it?

For that matter, why should dsa_ptr go in struct net_device and not in
the private state for the specific network drivers that need it?

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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