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From:   =?UTF-8?q?Linus=20L=C3=BCssing?= <linus.luessing@c0d3.blue>
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     linux-wireless@vger.kernel.org, b.a.t.m.a.n@lists.open-mesh.org,
        =?UTF-8?q?Linus=20L=C3=BCssing?= <ll@simonwunderlich.de>,
        Sven Eckelmann <sven@narfation.org>,
        Simon Wunderlich <sw@simonwunderlich.de>
Subject: [PATCH] iw: mesh: add mesh_param "mesh_nolearn" to skip path discovery
Date:   Tue, 16 Jun 2020 11:53:58 +0200
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From: Linus Lüssing <ll@simonwunderlich.de>

Currently, before being able to forward a packet between two 802.11s
nodes, both a PLINK handshake is performed upon receiving a beacon and
then later a PREQ/PREP exchange for path discovery is performed on
demand upon receiving a data frame to forward.

When running a mesh protocol on top of an 802.11s interface, like
batman-adv, we do not need the multi-hop mesh routing capabilities of
802.11s and usually set mesh_fwding=0. However, even with mesh_fwding=0
the PREQ/PREP path discovery is still performed on demand. Even though
in this scenario the next hop PREQ/PREP will determine is always the
direct 11s neighbor node.

The new mesh_nolearn parameter allows to skip the PREQ/PREP exchange in
this scenario, leading to a reduced delay, reduced packet buffering and
simplifies HWMP in general.

mesh_nolearn is still rather conservative in that if the packet destination
is not a direct 11s neighbor, it will fall back to PREQ/PREP path
discovery.

For normal, multi-hop 802.11s mesh routing it is usually not advisable
to enable mesh_nolearn as a transmission to a direct but distant neighbor
might be worse than reaching that same node via a more robust /
higher throughput etc. multi-hop path.

Cc: Sven Eckelmann <sven@narfation.org>
Cc: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Linus Lüssing <ll@simonwunderlich.de>
---
 mesh.c    | 2 ++
 nl80211.h | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/mesh.c b/mesh.c
index 0650d0c..48bbc3f 100644
--- a/mesh.c
+++ b/mesh.c
@@ -264,6 +264,8 @@ static const struct mesh_param_descr _mesh_param_descrs[] =
 	_my_nla_put_u16, _parse_u16, _print_u16_in_TUs},
 	{"mesh_plink_timeout", NL80211_MESHCONF_PLINK_TIMEOUT,
 	_my_nla_put_u32, _parse_u32, _print_u32_in_seconds},
+	{"mesh_nolearn", NL80211_MESHCONF_NOLEARN,
+	_my_nla_put_u8, _parse_u8_as_bool, _print_u8},
 };
 
 static void print_all_mesh_param_descr(void)
diff --git a/nl80211.h b/nl80211.h
index c14666b..4c55e89 100644
--- a/nl80211.h
+++ b/nl80211.h
@@ -4228,6 +4228,12 @@ enum nl80211_mesh_power_mode {
  *	field.  If left unset then the mesh formation field will only
  *	advertise such if there is an active root mesh path.
  *
+ * @NL80211_MESHCONF_NOLEARN: Try to avoid multi-hop path discovery (e.g.
+ *	PREQ/PREP for HWMP) if the destination is a direct neighbor. Note that
+ *	this might not be the optimal decision as a multi-hop route might be
+ *	better. So if using this setting you will likely also want to disable
+ *	dot11MeshForwarding and use another mesh routing protocol on top.
+ *
  * @__NL80211_MESHCONF_ATTR_AFTER_LAST: internal use
  */
 enum nl80211_meshconf_params {
@@ -4261,6 +4267,7 @@ enum nl80211_meshconf_params {
 	NL80211_MESHCONF_AWAKE_WINDOW,
 	NL80211_MESHCONF_PLINK_TIMEOUT,
 	NL80211_MESHCONF_CONNECTED_TO_GATE,
+	NL80211_MESHCONF_NOLEARN,
 
 	/* keep last */
 	__NL80211_MESHCONF_ATTR_AFTER_LAST,
-- 
2.27.0