Re: [PATCH 1/1] DSA Add callback to traffic control information

[Vladimir Oltean <olteanv@gmail.com>]

On Mon, Apr 11, 2022 at 02:23:59PM +0000, Geva, Erez wrote:
> As I mention, I do not own the tag driver code.
> 
> But for example for ETF, is like:
> 
> ... tag_xmit(struct sk_buff *skb, struct net_device *dev)
> +       struct tc_etf_qopt_offload etf;
> ...
> +       etf.queue = skb_get_queue_mapping(skb);
> +       if (dsa_slave_fetch_tc(dev, TC_SETUP_QDISC_ETF, &etf) == 0 && etf.enable) {
> ...
> 
> The port_fetch_tc callback is similar to port_setup_tc, only it reads the configuration instead of setting it.
> 
> I think it is easier to add a generic call back, so we do not need to add a new callback each time we support a new TC.
> 
> Erez

Since kernel v5.17 there exists struct dsa_device_ops :: connect() which
allows tagging protocol drivers to store persistent data for each switch.
Switch drivers also have a struct dsa_switch_ops :: connect_tag_protocol()
through which they can fix up or populate stuff in the tagging protocol
driver's private storage.
What you could do is set up something lockless, or even a function
pointer, to denote whether TX queue X is set up for ETF or not.

In any case, demanding that code with no in-kernel user gets accepted
will get a hard no, no matter how small it is.