Re: [PATCH] batman-adv: Map VID 0 to untagged TT VLAN

["Linus Lüssing" <linus.luessing@c0d3.blue>]

On Mon, Dec 16, 2024 at 07:37:12PM +0100, Sven Eckelmann wrote:
> diff --git a/net/batman-adv/main.c b/net/batman-adv/main.c
> index 8e0f44c71696f642d80304ec2724e8b5e56a5d93..333e947afcce7ca4128be8406f23295df723515c 100644
> --- a/net/batman-adv/main.c
> +++ b/net/batman-adv/main.c
> @@ -637,6 +637,13 @@ unsigned short batadv_get_vid(struct sk_buff *skb, size_t header_len)
>  
>  	vhdr = (struct vlan_ethhdr *)(skb->data + header_len);
>  	vid = ntohs(vhdr->h_vlan_TCI) & VLAN_VID_MASK;
> +
> +	/* VID 0 is only used to indicate "priority tag" frames which only
> +	 * contain priority information and no VID.
> +	 */
> +	if (vid == 0)
> +		return BATADV_NO_FLAGS;
> +
>  	vid |= BATADV_VLAN_HAS_TAG;
>  
>  	return vid;

I guess with this patch all TT entries previously in
TT VLAN 0 would be moved to untagged/NO_FLAGS TT entries, right?

Wouldn't that technically break compatibility? Let's say someone
uses VLAN headers with VID 0 to be able to use priorities / QoS.
What if some old nodes still announced+used VLAN 0 in batman-adv
while others used it after this patch, with the mapping to
NO_FLAGS?