batman-adv: Check hardif MTU against runtime MTU

If the MTU of the soft/mesh interface was already reduced (enough), it is
not necessary to print a warning about a hard interface not having a MTU to
transport ethernet payloads of 1500 bytes.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 41c1ad3..5a4ff9a 100644 (file)
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -9,6 +9,7 @@
 
 #include <linux/atomic.h>
 #include <linux/byteorder/generic.h>
+#include <linux/compiler.h>
 #include <linux/container_of.h>
 #include <linux/errno.h>
 #include <linux/gfp.h>
@@ -699,9 +700,14 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
        struct batadv_priv *bat_priv;
        __be16 ethertype = htons(ETH_P_BATMAN);
        int max_header_len = batadv_max_header_len();
+       unsigned int required_mtu;
+       unsigned int hardif_mtu;
        int ret;
 
-       if (hard_iface->net_dev->mtu < ETH_MIN_MTU + max_header_len)
+       hardif_mtu = READ_ONCE(hard_iface->net_dev->mtu);
+       required_mtu = READ_ONCE(soft_iface->mtu) + max_header_len;
+
+       if (hardif_mtu < ETH_MIN_MTU + max_header_len)
                return -EINVAL;
 
        if (hard_iface->if_status != BATADV_IF_NOT_IN_USE)
@@ -734,18 +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)
+           hardif_mtu < required_mtu)
                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);
+                           hard_iface->net_dev->name, hardif_mtu,
+                           required_mtu);
 
        if (!atomic_read(&bat_priv->fragmentation) &&
-           hard_iface->net_dev->mtu < ETH_DATA_LEN + max_header_len)
+           hardif_mtu < required_mtu)
                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);
+                           hard_iface->net_dev->name, hardif_mtu,
+                           required_mtu);
 
        if (batadv_hardif_is_iface_up(hard_iface))
                batadv_hardif_activate_interface(hard_iface);