Open-Mesh » batman-adv

Hello,

since I was not aware of this issue, I reported it as a bug in OpenWrt: https://github.com/openwrt/routing/issues/991

Are there any updates for this FR in the meantime?

No. Somebody has to add following patch and then figure out whether their are any limitations, problems, .... - and then of course fix them

From: Sven Eckelmann <sven@narfation.org>
Date: Tue, 18 Jul 2023 11:09:18 +0200
Subject: batman-adv: Add support for jumbo frames

TODO: write a commit message

Signed-off-by: Sven Eckelmann <sven@narfation.org>

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index a0c7fabd0b31d0c2e59dfdee0a703debc90bffe2..67bca22e62602f8f012984cb3fa3cb69140f26c0 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -613,10 +613,8 @@ int batadv_hardif_min_mtu(struct net_device *soft_iface)

     /* the real soft-interface MTU is computed by removing the payload
      * overhead from the maximum amount of bytes that was just computed.
-     *
-     * However batman-adv does not support MTUs bigger than ETH_DATA_LEN
      */
-    return min_t(int, min_mtu - batadv_max_header_len(), ETH_DATA_LEN);
+    return min_t(int, min_mtu - batadv_max_header_len(), BATADV_MAX_MTU);
 }

 /**
@@ -742,18 +740,18 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
             hard_iface->net_dev->name);

     if (atomic_read(&bat_priv->fragmentation) &&
-        hard_iface->net_dev->mtu < ETH_DATA_LEN + max_header_len)
+        hard_iface->net_dev->mtu < BATADV_MAX_MTU + max_header_len)
         batadv_info(hard_iface->soft_iface,
                 "The MTU of interface %s is too small (%i) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to %i would solve the problem.\n",
                 hard_iface->net_dev->name, hard_iface->net_dev->mtu,
-                ETH_DATA_LEN + max_header_len);
+                BATADV_MAX_MTU + max_header_len);

     if (!atomic_read(&bat_priv->fragmentation) &&
-        hard_iface->net_dev->mtu < ETH_DATA_LEN + max_header_len)
+        hard_iface->net_dev->mtu < BATADV_MAX_MTU + max_header_len)
         batadv_info(hard_iface->soft_iface,
                 "The MTU of interface %s is too small (%i) to handle the transport of batman-adv packets. If you experience problems getting traffic through try increasing the MTU to %i.\n",
                 hard_iface->net_dev->name, hard_iface->net_dev->mtu,
-                ETH_DATA_LEN + max_header_len);
+                BATADV_MAX_MTU + max_header_len);

     if (batadv_hardif_is_iface_up(hard_iface))
         batadv_hardif_activate_interface(hard_iface);
diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h
index 494d1ebecac2b6d4649ff28e10b5c53183cc0fde..68fa46105e5a18bec3554ffed7fa5d0e711229b4 100644
--- a/net/batman-adv/main.h
+++ b/net/batman-adv/main.h
@@ -22,6 +22,8 @@
 #define BATADV_THROUGHPUT_MAX_VALUE 0xFFFFFFFF
 #define BATADV_JITTER 20

+#define BATADV_MAX_MTU (ETH_MAX_MTU - batadv_max_header_len())
+
 /* Time To Live of broadcast messages */
 #define BATADV_TTL 50

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index fd0a3a48626af3830f83967f3b028495e49e4172..4e4d744f4eb446d0d1728041d698290c0aa753b4 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -157,7 +157,7 @@ static int batadv_interface_change_mtu(struct net_device *dev, int new_mtu)
     struct batadv_priv *bat_priv = netdev_priv(dev);

     /* check ranges */
-    if (new_mtu < 68 || new_mtu > batadv_hardif_min_mtu(dev))
+    if (new_mtu < ETH_MIN_MTU || new_mtu > batadv_hardif_min_mtu(dev))
         return -EINVAL;

     dev->mtu = new_mtu;
@@ -774,7 +774,7 @@ static int batadv_softif_init_late(struct net_device *dev)
     atomic_set(&bat_priv->log_level, 0);
 #endif
     atomic_set(&bat_priv->fragmentation, 1);
-    atomic_set(&bat_priv->packet_size_max, ETH_DATA_LEN);
+    atomic_set(&bat_priv->packet_size_max, BATADV_MAX_MTU);
     atomic_set(&bat_priv->bcast_queue_left, BATADV_BCAST_QUEUE_LEN);
     atomic_set(&bat_priv->batman_queue_left, BATADV_BATMAN_QUEUE_LEN);

@@ -1014,6 +1014,7 @@ static void batadv_softif_init_early(struct net_device *dev)
      * have not been initialized yet
      */
     dev->mtu = ETH_DATA_LEN;
+    dev->max_mtu = BATADV_MAX_MTU;

     /* generate random address */
     eth_hw_addr_random(dev);

Especially for broadcast, multicast (optimization), TT, network coding, OGMs, ELPs, ...

And definitely open questions are:

• what to do with the "The MTU of interface XXX" is too small messages? Because it will now warn all the time because no(?) interface will be able to transport 2**16-1 bytes. Maybe we should leave the checks to ETH_DATA_LEN in batadv_hardif_enable_interface?

The RFC can be found at:

• https://patchwork.open-mesh.org/project/b.a.t.m.a.n./list/?series=539
• https://lore.kernel.org/r/20230727-jumbo-mtu-v1-0-036ce1a6e33c@narfation.org