Re: [B.A.T.M.A.N.] [PATCH 3/3] batman-adv: Modified forwarding behaviour for multicast packets

[Antonio Quartulli <ordex@autistici.org>]

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On Sat, May 11, 2013 at 07:23:27PM +0200, Linus Lüssing wrote:
> With this patch a multicast packet is not always simply flooded anymore,
> the bevahiour for the following cases is changed to reduce
> unnecessary overhead:
> 
> If all nodes within the horizon of a certain node have signalized
> multicast listener announcement capability
> (BATADV_MCAST_LISTENER_ANNOUNCEMENT) then an IPv6 multicast packet
> with a destination of IPv6 link-local scope coming from the upstream
> of this node...
> 
> * ...is dropped if there is no according multicast listener in the
>   translation table.
> * ...is forwarded via unicast if there is a single node with interested
>   multicast listeners.
> 

othwerwise? Does it get flooded like now if there is more than one receiver?

>  
>  /**
> + * batadv_mcast_flood - Checks on how to forward a multicast packet
> + * @skb: The multicast packet to check
> + * @bat_priv: the bat priv with all the soft interface information
> + *
> + * Returns 1 if the packet should be flooded, 0 if it should be forwarded
> + * via unicast or -1 if it should be drooped.
> + */
> +int batadv_mcast_flood(struct sk_buff *skb, struct batadv_priv *bat_priv)
> +{
> +	struct ethhdr *ethhdr = (struct ethhdr *)(skb->data);
> +	struct ipv6hdr *ip6hdr;
> +	int count, ret = 1;
> +
> +	if (atomic_read(&bat_priv->mcast_group_awareness) &&
> +	    !atomic_read(&bat_priv->mcast_num_non_aware) &&
> +	    ntohs(ethhdr->h_proto) == ETH_P_IPV6) {

mh..this would not work for VLANs..did you plan to introduce support for VLANs
later? or you simply overlooked it? :)

> +		if (!pskb_may_pull(skb, sizeof(*ethhdr) + sizeof(*ip6hdr))) {
> +			ret = -1;
> +			goto out;
> +		}
> +
> +		ip6hdr = ipv6_hdr(skb);
> +
> +		/* TODO: Implement Multicast Router Discovery, then add
> +		 * scope >= IPV6_ADDR_SCOPE_LINKLOCAL, too */
> +		if (IPV6_ADDR_MC_SCOPE(&ip6hdr->daddr) !=
> +		    IPV6_ADDR_SCOPE_LINKLOCAL)
> +			goto out;
> +
> +		count = batadv_tt_global_hash_count(bat_priv, ethhdr->h_dest);
> +
> +		if (!count)
> +			ret = -1;
> +		else if (count == 1)
> +			ret = 0;

how can this function return more than one?
When there is more than one originator announcing the same MAC address then we
have _a single_ global entry having a list of orig_entry. but stil only one
global entry.

so you may want to count the orig_entries rather than the global_entries?

> diff --git a/translation-table.c b/translation-table.c
> index 37e7d47..1d2d618 100644
> --- a/translation-table.c
> +++ b/translation-table.c
> @@ -83,6 +83,40 @@ batadv_tt_hash_find(struct batadv_hashtable *hash, const void *data)
>  	return tt_common_entry_tmp;
>  }
>  
> +/**
> + * batadv_tt_hash_count - Counts the number of tt entries for the given data
> + * @hash: hash table containing the tt entries
> + * @data: The data to count entries for

One line saying what you are returning would be nice :)

> + */
> +static int batadv_tt_hash_count(struct batadv_hashtable *hash, const void *data)
> +{
> +	struct hlist_head *head;
> +	struct batadv_tt_common_entry *tt_common_entry;
> +	uint32_t index;
> +	int count = 0;
> +
> +	if (!hash)
> +		goto out;
> +
> +	index = batadv_choose_orig(data, hash->size);
> +	head = &hash->table[index];
> +
> +	rcu_read_lock();
> +	hlist_for_each_entry_rcu(tt_common_entry, head, hash_entry) {
> +		if (!batadv_compare_eth(tt_common_entry, data))
> +			continue;
> +
> +		if (!atomic_read(&tt_common_entry->refcount))
> +			continue;
> +
> +		count++;
> +	}
> +	rcu_read_unlock();
> +
> +out:
> +	return count;
> +}

as I asked before: this function cannot return >1 because the same address is
never stored twice.


Nice job so far!
Thanks for working on this cool feature!

Cheers,

-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

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