Staging: batman-adv: layer2 unicast packet fragmentation

This patch implements a simple layer2 fragmentation to allow traffic
exchange over network interfaces with a MTU smaller than 1500 bytes. The
fragmentation splits the big packets into two parts and marks the frames
accordingly. The receiving end buffers the packets to reassemble the
orignal packet before passing it to the higher layers. This feature
makes it necessary to modify the batman-adv encapsulation for unicast
packets by adding a sequence number, flags and the originator address.
This modifcation is part of a seperate packet type for fragemented
packets to keep the original overhead as low as possible. This patch
enables the feature by default to ensure the data traffic can travel
through the network. But it also prints a warning to notify the user
about the performance implications.

Note: Fragmentation should be avoided at all costs since it has a
dramatic impact on the performance, especially when it comes wifi
networks. Instead of a single packet, 2 packets have to be sent! Not
only valuable airtime is wasted but also packetloss decreases the
throughput. A link with 50% packetloss and fragmentation enabled is
pretty much unusable.

Signed-off-by: Andreas Langer <an.langer@gmx.de>
[sven.eckelmann@gmx.de: Rework on top of current version]
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 55 insertions, 0 deletions

diff --git a/drivers/staging/batman-adv/bat_sysfs.c b/drivers/staging/batman-adv/bat_sysfs.c
index d49adde..b9fe391 100644
--- a/drivers/staging/batman-adv/bat_sysfs.c
+++ b/drivers/staging/batman-adv/bat_sysfs.c
@@ -134,6 +134,58 @@ static ssize_t store_bond(struct kobject *kobj, struct attribute *attr,
 	return count;
 }
 
+static ssize_t show_frag(struct kobject *kobj, struct attribute *attr,
+			     char *buff)
+{
+	struct device *dev = to_dev(kobj->parent);
+	struct bat_priv *bat_priv = netdev_priv(to_net_dev(dev));
+	int frag_status = atomic_read(&bat_priv->frag_enabled);
+
+	return sprintf(buff, "%s\n",
+		       frag_status == 0 ? "disabled" : "enabled");
+}
+
+static ssize_t store_frag(struct kobject *kobj, struct attribute *attr,
+			  char *buff, size_t count)
+{
+	struct device *dev = to_dev(kobj->parent);
+	struct net_device *net_dev = to_net_dev(dev);
+	struct bat_priv *bat_priv = netdev_priv(net_dev);
+	int frag_enabled_tmp = -1;
+
+	if (((count == 2) && (buff[0] == '1')) ||
+	    (strncmp(buff, "enable", 6) == 0))
+		frag_enabled_tmp = 1;
+
+	if (((count == 2) && (buff[0] == '0')) ||
+	    (strncmp(buff, "disable", 7) == 0))
+		frag_enabled_tmp = 0;
+
+	if (frag_enabled_tmp < 0) {
+		if (buff[count - 1] == '\n')
+			buff[count - 1] = '\0';
+
+		bat_err(net_dev,
+			"Invalid parameter for 'fragmentation' setting on mesh"
+			"received: %s\n", buff);
+		return -EINVAL;
+	}
+
+	if (atomic_read(&bat_priv->frag_enabled) == frag_enabled_tmp)
+		return count;
+
+	bat_info(net_dev, "Changing fragmentation from: %s to: %s\n",
+		 atomic_read(&bat_priv->frag_enabled) == 1 ?
+		 "enabled" : "disabled",
+		 frag_enabled_tmp == 1 ? "enabled" : "disabled");
+
+	atomic_set(&bat_priv->frag_enabled, (unsigned)frag_enabled_tmp);
+
+	update_min_mtu();
+
+	return count;
+}
+
 static ssize_t show_vis_mode(struct kobject *kobj, struct attribute *attr,
 			     char *buff)
 {
@@ -279,6 +331,7 @@ static ssize_t store_log_level(struct kobject *kobj, struct attribute *attr,
 static BAT_ATTR(aggregated_ogms, S_IRUGO | S_IWUSR,
 		show_aggr_ogms, store_aggr_ogms);
 static BAT_ATTR(bonding, S_IRUGO | S_IWUSR, show_bond, store_bond);
+static BAT_ATTR(fragmentation, S_IRUGO | S_IWUSR, show_frag, store_frag);
 static BAT_ATTR(vis_mode, S_IRUGO | S_IWUSR, show_vis_mode, store_vis_mode);
 static BAT_ATTR(orig_interval, S_IRUGO | S_IWUSR,
 		show_orig_interval, store_orig_interval);
@@ -289,6 +342,7 @@ static BAT_ATTR(log_level, S_IRUGO | S_IWUSR, show_log_level, store_log_level);
 static struct bat_attribute *mesh_attrs[] = {
 	&bat_attr_aggregated_ogms,
 	&bat_attr_bonding,
+	&bat_attr_fragmentation,
 	&bat_attr_vis_mode,
 	&bat_attr_orig_interval,
 #ifdef CONFIG_BATMAN_ADV_DEBUG
@@ -308,6 +362,7 @@ int sysfs_add_meshif(struct net_device *dev)
 		  routine as soon as we have it */
 	atomic_set(&bat_priv->aggregation_enabled, 1);
 	atomic_set(&bat_priv->bonding_enabled, 0);
+	atomic_set(&bat_priv->frag_enabled, 1);
 	atomic_set(&bat_priv->vis_mode, VIS_TYPE_CLIENT_UPDATE);
 	atomic_set(&bat_priv->orig_interval, 1000);
 	atomic_set(&bat_priv->log_level, 0);