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[2/2] batman-adv: Don't increase MTU when set by user

Message ID 20230719-mtu-v1-2-48fd024f0f56@narfation.org (mailing list archive)
State Accepted, archived
Delegated to: Simon Wunderlich
Headers
Series batman-adv: Fix MTU handling |

Commit Message

Sven Eckelmann July 19, 2023, 8:15 a.m. UTC 
  If the user set an MTU value, it usually means that there are special
requirements for the MTU. But if an interface gots activated, the MTU was
always recalculated and then the user set value was overwritten.

The only reason why this user set value has to be overwritten, is when the
MTU has to be decreased because batman-adv is not able to transfer packets
with the user specified size.

Fixes: 88861ea9acb7 ("[batman-adv] replacing if up/down timer with kernel notifications")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/hard-interface.c | 14 +++++++++++++-
 net/batman-adv/soft-interface.c |  3 +++
 net/batman-adv/types.h          |  6 ++++++
 3 files changed, 22 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index ae5762af..24c9c0c3 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -630,7 +630,19 @@  int batadv_hardif_min_mtu(struct net_device *soft_iface)
  */
 void batadv_update_min_mtu(struct net_device *soft_iface)
 {
-	dev_set_mtu(soft_iface, batadv_hardif_min_mtu(soft_iface));
+	struct batadv_priv *bat_priv = netdev_priv(soft_iface);
+	int limit_mtu;
+	int mtu;
+
+	mtu = batadv_hardif_min_mtu(soft_iface);
+
+	if (bat_priv->mtu_set_by_user)
+		limit_mtu = bat_priv->mtu_set_by_user;
+	else
+		limit_mtu = ETH_DATA_LEN;
+
+	mtu = min(mtu, limit_mtu);
+	dev_set_mtu(soft_iface, mtu);
 
 	/* Check if the local translate table should be cleaned up to match a
 	 * new (and smaller) MTU.
diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index d3fdf822..85d00dc9 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -153,11 +153,14 @@  static int batadv_interface_set_mac_addr(struct net_device *dev, void *p)
 
 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))
 		return -EINVAL;
 
 	dev->mtu = new_mtu;
+	bat_priv->mtu_set_by_user = new_mtu;
 
 	return 0;
 }
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index ca9449ec..cf1a0eaf 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -1546,6 +1546,12 @@  struct batadv_priv {
 	/** @soft_iface: net device which holds this struct as private data */
 	struct net_device *soft_iface;
 
+	/**
+	 * @mtu_set_by_user: MTU was set once by user
+	 * protected by rtnl_lock
+	 */
+	int mtu_set_by_user;
+
 	/**
 	 * @bat_counters: mesh internal traffic statistic counters (see
 	 *  batadv_counters)