Re: [B.A.T.M.A.N.] [PATCHv2] batman-adv: forward late OGMs from best next hop

["Linus Lüssing" <linus.luessing@web.de>]

Hi Simon,

I'm currently wondering whether changing the protocol in the way
you described is sufficient.

I think it still has the problem of not converging to the optimal
solution in various scenarios, for instance:

----------

    B1 ---------
  /             \        
A        C1 ---- D
  \    /        /
    B2 - C2 ----

A-B1:   10%, 0ms
A-B2:  100%, 0ms
B2-C1:   5%, 0ms
B2-C2: 100%, 5ms
B1-D:  100%, 0ms
C1-D:  100%, 0ms
C2-D:  100%, 0ms
('link': 'link-quality', 'link-delay')

Obviously, here the path A-B2-C2 is the best, having a 100% link
quality. However with this patch, it will select A-B1-D, having
only a 10% link quality (I'm not considering asym/hop-penalty or
that 0ms delay is unrealistic, and I'm not considering that the
link quality will cause lost OGMs - just to keep things simple):


The OGM from D gets forwarded to B1 and then to A instantly; A
notes a path quality of 10% towards D via B1.

The OGM from D reaches B2 via C1 first, so B2 first forwards an
OGM with a path quality of 5% to A first. A notes a path quality
of 5% towards D via B2.

Then the OGM from D reaches B2 via C2, too. Now, with this patch
B2 will correctly choose the path via C2, B2 notes a 100% path
quality towards D via C2 instead of ignoring this OGM. And B2 will
also rebroadcast this OGM.

However, A will ignore this second OGM from D via B2 because it
came from the same neighbor even though it came from the best,
optimal, 100% link-quality path.

----------

While converging to a path after applying this patch is obviously
better than the starvation which can currently happen I'm
still wondering whether the issue could be solved better.

What if we were always rebroadcasting/forwarding an OGM even from
the same neighbor, too, if the sequence number is the same but the
TQ better (so similar to what is specified for BATMAN V)?


Cheers, Linus


On Thu, May 23, 2013 at 01:07:42PM +0200, Simon Wunderlich wrote:
> From: Simon Wunderlich <simon@open-mesh.com>
> 
> When a packet is received from another node first and later from the
> best next hop, this packet is dropped. However the first OGM was sent
> with the BATADV_NOT_BEST_NEXT_HOP flag and thus dropped by neighbors.
> The late OGM from the best neighbor is then dropped because it is a
> duplicate.
> 
> If this situation happens constantly, a node might end up not forwarding
> the "valid" OGMs anymore, and nodes behind will starve from not getting
> valid OGMs.
> 
> Fix this by refining the duplicate checking behaviour: The actions
> should depend on whether it was a duplicate for a neighbor only or for
> the originator. OGMs which are not duplicates for a specific neighbor
> will now be considered in batadv_iv_ogm_forward(), but only actually
> forwarded for the best next hop. Therefore, late OGMs from the best
> next hop are forwarded now and not dropped as duplicates anymore.
> 
> Signed-off-by: Simon Wunderlich <simon@open-mesh.com>
> 
> ---
> Changes to PATCHv1:
>  * use enum to distinguish different duplicate states
>  * fix typo "is_simlar -> is_similar"
>  * remove antonios sign off (the patch changed, feel free to add it if
>    he is ok with it, it was his idea originally ...)
> ---
>  bat_iv_ogm.c |   86 +++++++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 55 insertions(+), 31 deletions(-)
> 
> diff --git a/bat_iv_ogm.c b/bat_iv_ogm.c
> index 8d87f87..2b94fdd 100644
> --- a/bat_iv_ogm.c
> +++ b/bat_iv_ogm.c
> @@ -701,6 +701,21 @@ static void batadv_iv_ogm_schedule(struct batadv_hard_iface *hard_iface)
>  		batadv_hardif_free_ref(primary_if);
>  }
>  
> +/**
> + * batadv_dup_status - duplicate status
> + * @BATADV_NO_DUP: the packet is a duplicate
> + * @BATADV_ORIG_DUP: OGM is a duplicate in the originator (but not for the
> + *  neighbor)
> + * @BATADV_NEIGH_DUP: OGM is a duplicate for the neighbor
> + * @BATADV_PROTECTED: originator is currently protected (after reboot)
> + */
> +enum batadv_dup_status {
> +	BATADV_NO_DUP = 0,
> +	BATADV_ORIG_DUP,
> +	BATADV_NEIGH_DUP,
> +	BATADV_PROTECTED,
> +};
> +
>  static void
>  batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv,
>  			  struct batadv_orig_node *orig_node,
> @@ -708,7 +723,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv,
>  			  const struct batadv_ogm_packet *batadv_ogm_packet,
>  			  struct batadv_hard_iface *if_incoming,
>  			  const unsigned char *tt_buff,
> -			  int is_duplicate)
> +			  enum batadv_dup_status dup_status)
>  {
>  	struct batadv_neigh_node *neigh_node = NULL, *tmp_neigh_node = NULL;
>  	struct batadv_neigh_node *router = NULL;
> @@ -734,7 +749,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv,
>  			continue;
>  		}
>  
> -		if (is_duplicate)
> +		if (dup_status != BATADV_NO_DUP)
>  			continue;
>  
>  		spin_lock_bh(&tmp_neigh_node->lq_update_lock);
> @@ -774,7 +789,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv,
>  	neigh_node->tq_avg = batadv_ring_buffer_avg(neigh_node->tq_recv);
>  	spin_unlock_bh(&neigh_node->lq_update_lock);
>  
> -	if (!is_duplicate) {
> +	if (dup_status == BATADV_NO_DUP) {
>  		orig_node->last_ttl = batadv_ogm_packet->header.ttl;
>  		neigh_node->last_ttl = batadv_ogm_packet->header.ttl;
>  	}
> @@ -932,15 +947,16 @@ out:
>  	return ret;
>  }
>  
> -/* processes a batman packet for all interfaces, adjusts the sequence number and
> - * finds out whether it is a duplicate.
> +/**
> + * batadv_iv_ogm_update_seqnos -  processes a batman packet for all interfaces,
> + *  adjusts the sequence number and finds out whether it is a duplicate.
> + * @ethhdr: Ethernet header of the packet
> + * @batadv_ogm_packet: OGM packet to be considered
> + * @if_incoming: interface where the OGM packet was received
> + * Returns: duplicate status as enum batadv_dup_status
>   * returns:
> - *   1 the packet is a duplicate
> - *   0 the packet has not yet been received
> - *  -1 the packet is old and has been received while the seqno window
> - *     was protected. Caller should drop it.
> - */
> -static int
> +  */
> +enum batadv_dup_status
>  batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr,
>  			    const struct batadv_ogm_packet *batadv_ogm_packet,
>  			    const struct batadv_hard_iface *if_incoming)
> @@ -948,17 +964,18 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr,
>  	struct batadv_priv *bat_priv = netdev_priv(if_incoming->soft_iface);
>  	struct batadv_orig_node *orig_node;
>  	struct batadv_neigh_node *tmp_neigh_node;
> -	int is_duplicate = 0;
> +	int is_dup;
>  	int32_t seq_diff;
>  	int need_update = 0;
> -	int set_mark, ret = -1;
> +	int set_mark;
> +	enum batadv_dup_status ret = BATADV_NO_DUP;
>  	uint32_t seqno = ntohl(batadv_ogm_packet->seqno);
>  	uint8_t *neigh_addr;
>  	uint8_t packet_count;
>  
>  	orig_node = batadv_get_orig_node(bat_priv, batadv_ogm_packet->orig);
>  	if (!orig_node)
> -		return 0;
> +		return BATADV_NO_DUP;
>  
>  	spin_lock_bh(&orig_node->ogm_cnt_lock);
>  	seq_diff = seqno - orig_node->last_real_seqno;
> @@ -966,22 +983,29 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr,
>  	/* signalize caller that the packet is to be dropped. */
>  	if (!hlist_empty(&orig_node->neigh_list) &&
>  	    batadv_window_protected(bat_priv, seq_diff,
> -				    &orig_node->batman_seqno_reset))
> +				    &orig_node->batman_seqno_reset)) {
> +		ret = BATADV_PROTECTED;
>  		goto out;
> +	}
>  
>  	rcu_read_lock();
>  	hlist_for_each_entry_rcu(tmp_neigh_node,
>  				 &orig_node->neigh_list, list) {
> -		is_duplicate |= batadv_test_bit(tmp_neigh_node->real_bits,
> -						orig_node->last_real_seqno,
> -						seqno);
> -
>  		neigh_addr = tmp_neigh_node->addr;
> +		is_dup = batadv_test_bit(tmp_neigh_node->real_bits,
> +					 orig_node->last_real_seqno,
> +					 seqno);
> +
>  		if (batadv_compare_eth(neigh_addr, ethhdr->h_source) &&
> -		    tmp_neigh_node->if_incoming == if_incoming)
> +		    tmp_neigh_node->if_incoming == if_incoming) {
>  			set_mark = 1;
> -		else
> +			if (is_dup)
> +				ret = BATADV_NEIGH_DUP;
> +		} else {
>  			set_mark = 0;
> +			if (is_dup && (ret != BATADV_NEIGH_DUP))
> +				ret = BATADV_ORIG_DUP;
> +		}
>  
>  		/* if the window moved, set the update flag. */
>  		need_update |= batadv_bit_get_packet(bat_priv,
> @@ -1001,8 +1025,6 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr,
>  		orig_node->last_real_seqno = seqno;
>  	}
>  
> -	ret = is_duplicate;
> -
>  out:
>  	spin_unlock_bh(&orig_node->ogm_cnt_lock);
>  	batadv_orig_node_free_ref(orig_node);
> @@ -1024,7 +1046,8 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr,
>  	int is_bidirect;
>  	bool is_single_hop_neigh = false;
>  	bool is_from_best_next_hop = false;
> -	int is_duplicate, sameseq, simlar_ttl;
> +	int sameseq, similar_ttl;
> +	enum batadv_dup_status dup_status;
>  	uint32_t if_incoming_seqno;
>  	uint8_t *prev_sender;
>  
> @@ -1149,10 +1172,10 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr,
>  	if (!orig_node)
>  		return;
>  
> -	is_duplicate = batadv_iv_ogm_update_seqnos(ethhdr, batadv_ogm_packet,
> -						   if_incoming);
> +	dup_status = batadv_iv_ogm_update_seqnos(ethhdr, batadv_ogm_packet,
> +						 if_incoming);
>  
> -	if (is_duplicate == -1) {
> +	if (dup_status == BATADV_PROTECTED) {
>  		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
>  			   "Drop packet: packet within seqno protection time (sender: %pM)\n",
>  			   ethhdr->h_source);
> @@ -1224,11 +1247,12 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr,
>  	 * seqno and similar ttl as the non-duplicate
>  	 */
>  	sameseq = orig_node->last_real_seqno == ntohl(batadv_ogm_packet->seqno);
> -	simlar_ttl = orig_node->last_ttl - 3 <= batadv_ogm_packet->header.ttl;
> -	if (is_bidirect && (!is_duplicate || (sameseq && simlar_ttl)))
> +	similar_ttl = orig_node->last_ttl - 3 <= batadv_ogm_packet->header.ttl;
> +	if (is_bidirect && ((dup_status == BATADV_NO_DUP) ||
> +			    (sameseq && similar_ttl)))
>  		batadv_iv_ogm_orig_update(bat_priv, orig_node, ethhdr,
>  					  batadv_ogm_packet, if_incoming,
> -					  tt_buff, is_duplicate);
> +					  tt_buff, dup_status);
>  
>  	/* is single hop (direct) neighbor */
>  	if (is_single_hop_neigh) {
> @@ -1249,7 +1273,7 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr,
>  		goto out_neigh;
>  	}
>  
> -	if (is_duplicate) {
> +	if (dup_status == BATADV_NEIGH_DUP) {
>  		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
>  			   "Drop packet: duplicate packet received\n");
>  		goto out_neigh;
> -- 
> 1.7.10.4
>