netdev - Re: [net 3/3] can: isotp: add SF_BROADCAST support for functional addressing

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Date:   Fri, 4 Dec 2020 19:44:35 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        linux-can@...r.kernel.org, kernel@...gutronix.de,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Thomas Wagner <thwa1@....de>
Subject: Re: [net 3/3] can: isotp: add SF_BROADCAST support for functional
 addressing

On Fri,  4 Dec 2020 14:35:08 +0100 Marc Kleine-Budde wrote:
> From: Oliver Hartkopp <socketcan@...tkopp.net>
> 
> When CAN_ISOTP_SF_BROADCAST is set in the CAN_ISOTP_OPTS flags the CAN_ISOTP
> socket is switched into functional addressing mode, where only single frame
> (SF) protocol data units can be send on the specified CAN interface and the
> given tp.tx_id after bind().
> 
> In opposite to normal and extended addressing this socket does not register a
> CAN-ID for reception which would be needed for a 1-to-1 ISOTP connection with a
> segmented bi-directional data transfer.
> 
> Sending SFs on this socket is therefore a TX-only 'broadcast' operation.

Unclear from this patch what is getting fixed. Looks a little bit like
a feature which could be added in a backward compatible way, no?
Is it only added for completeness of the ISOTP implementation?