batman-adv: Add fragmentation mesh genl configuration

The mesh interface can fragment unicast packets when the packet size
exceeds the outgoing slave/hard-interface MTU.

The BATADV_CMD_SET_MESH/BATADV_CMD_GET_MESH commands allow to set/get the
configuration of this feature using the BATADV_ATTR_FRAGMENTATION_ENABLED
attribute. Setting the u8 to zero will disable this feature and setting it
to something else is enabling this feature.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

include/uapi/linux/batman_adv.h

@@ -396,6 +396,13 @@ enum batadv_nl_attrs {
 	 */
 	BATADV_ATTR_DISTRIBUTED_ARP_TABLE_ENABLED,
 
+	/**
+	 * @BATADV_ATTR_FRAGMENTATION_ENABLED: whether the data traffic going
+	 *  through the mesh will be fragmented or silently discarded if the
+	 *  packet size exceeds the outgoing interface MTU.
+	 */
+	BATADV_ATTR_FRAGMENTATION_ENABLED,
+
 	/* add attributes above here, update the policy in netlink.c */
 
 	/**

net/batman-adv/netlink.c

@@ -146,6 +146,7 @@ static const struct nla_policy batadv_netlink_policy[NUM_BATADV_ATTR] = {
 	[BATADV_ATTR_BONDING_ENABLED]		= { .type = NLA_U8 },
 	[BATADV_ATTR_BRIDGE_LOOP_AVOIDANCE_ENABLED]	= { .type = NLA_U8 },
 	[BATADV_ATTR_DISTRIBUTED_ARP_TABLE_ENABLED]	= { .type = NLA_U8 },
+	[BATADV_ATTR_FRAGMENTATION_ENABLED]	= { .type = NLA_U8 },
 };
 
 /**
@@ -298,6 +299,10 @@ static int batadv_netlink_mesh_fill(struct sk_buff *msg,
 		goto nla_put_failure;
 #endif /* CONFIG_BATMAN_ADV_DAT */
 
+	if (nla_put_u8(msg, BATADV_ATTR_FRAGMENTATION_ENABLED,
+		       !!atomic_read(&bat_priv->fragmentation)))
+		goto nla_put_failure;
+
 	if (primary_if)
 		batadv_hardif_put(primary_if);
 
@@ -432,6 +437,13 @@ static int batadv_netlink_set_mesh(struct sk_buff *skb, struct genl_info *info)
 	}
 #endif /* CONFIG_BATMAN_ADV_DAT */
 
+	if (info->attrs[BATADV_ATTR_FRAGMENTATION_ENABLED]) {
+		attr = info->attrs[BATADV_ATTR_FRAGMENTATION_ENABLED];
+
+		atomic_set(&bat_priv->fragmentation, !!nla_get_u8(attr));
+		batadv_update_min_mtu(bat_priv->soft_iface);
+	}
+
 	batadv_netlink_notify_mesh(bat_priv);
 
 	return 0;