[batadv,v12 4/5] batman-adv: avoid superfluous DAT DHT_PUT if self-candidate

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

If we are one of the three closest DAT DHT candidates for a given IPv4
address then three DHT_PUTs to three remote DAT DHT candidates, especially
the last selected DAT DHT candidate, is unnecessary: A DAT DHT_GET from
another node would typically not get to it anyway and would reach us
instead. Because the remote node will take us into account, while we so
far don't take ourself into account in batadv_choose_next_candidate().

Instead of reworking batadv_choose_next_candidate() to take ourself into
account, too, simply, potentially kick out the "worst" remote candidate
at the end of calculation if we are a better candidate. To avoid an
unnecessary DAT DHT_PUT / DHT_GET transmission.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
---
 net/batman-adv/distributed-arp-table.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 321df338fb8d..52dff46a7c52 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -779,6 +779,9 @@ static void batadv_choose_next_candidate(struct batadv_priv *bat_priv,
  * Check if we are a better candidate than the last placed, selected DHT
  * candidate for the given IP address key.
  *
+ * If we are a better candidate then deselects the last placed, selected
+ * DHT candidate.
+ *
  * Return: true if we are a better candidate, false otherwise.
  */
 static bool batadv_dat_cmp_self_candidate(struct batadv_priv *bat_priv,
@@ -822,6 +825,14 @@ static bool batadv_dat_cmp_self_candidate(struct batadv_priv *bat_priv,
 	    memcmp(own_orig_addr, last_cand->orig_node->orig, ETH_ALEN) >= 0)
 		goto out;
 
+	/* deselect last placed, selected candidate, we take its spot */
+	batadv_dbg(BATADV_DBG_DAT, bat_priv,
+		   "%s(): deselecting %pM for hash(IP)=%u\n",
+		   __func__, last_cand->orig_node->orig, ip_key);
+
+	last_cand->type = BATADV_DAT_CANDIDATE_NOT_FOUND;
+	batadv_orig_node_put(last_cand->orig_node);
+
 	ret = true;
 out:
 	if (ret)
-- 
2.55.0