Re: [PATCH net-next 01/10] batman-adv: dat: drop non-4addr backwards compatibility

[Sven Eckelmann <sven@narfation.org>]

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https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260805143200.722098-1-sw%40simonwunderlich.de?part=1

> --- Patch [1]: [PATCH net-next 01/10] batman-adv: dat: drop non-4addr backwards compatibility ---
[...]
> Discovered by: opus-5 · Missed by: old-prompts, sashiko-gemini · Confirmed by: old-prompts
> Was the removed else branch really only reachable when talking to
> pre-compat-15 nodes?

This is a misrepresentation of the commit. The code was added in batman-adv 
with compat 14 when not all nodes had support for 4-addr packets. 
With compat-15, all nodes must have support for 4addr packets and the 
backwards compatibility hack is no longer needed

[...]
> After this change those cache replies go out as BATADV_UNICAST_4ADDR, and on
> the receiver batadv_recv_unicast_packet() now takes the is4addr path:
> 
> 			subtype = unicast_4addr_packet->subtype;
> 			batadv_dat_inc_counter(bat_priv, subtype);
> 
> so BATADV_P_DAT_CACHE_REPLY RX accounting is incremented where it previously
> was not, and the encapsulation of these replies changes in packet captures.

Yes, but what is wrong about the correct packets and correct accounting?

[...] 
> Discovered by: opus-5 · Missed by: old-prompts, sashiko-gemini · Confirmed by: old-prompts
> This is a pre-existing issue and not introduced by this patch, but while
> looking at the DAT subtype decoding: the default arm of the inner switch in
> batadv_dbg_arp() prints the packet type where the message says subtype:
> 
> 		switch (unicast_4addr_packet->subtype) {
> 		...
> 		default:
> 			batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: Unknown (%u)!\n",
> 				   unicast_4addr_packet->u.packet_type);
> 		}
> 
> That arm is only reachable from case BATADV_UNICAST_4ADDR: of the outer
> switch, so the value printed is always 0x42 rather than the unrecognized
> value from enum batadv_subtype in include/uapi/linux/batadv_packet.h.

Irrelevant for this patch but I've submitted a mini fix:
https://patchwork.open-mesh.org/project/b.a.t.m.a.n./patch/20260806-4addr-unknown-subtype-print-v1-1-e906357a5895@narfation.org/

Regards,
	Sven


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