wprobe: move measurement task to the kernel, add some configurability (work in progress)

SVN-Revision: 16402

9 files changed, 475 insertions, 155 deletions

diff --git a/package/wprobe/Makefile b/package/wprobe/Makefile
index fe96512..a28ad93 100644
--- a/package/wprobe/Makefile
+++ b/package/wprobe/Makefile
@@ -45,7 +45,7 @@ endef
 define Package/wprobe-export
   SECTION:=net
   CATEGORY:=Network
-  DEPENDS:=+kmod-wprobe +libnl-tiny
+  DEPENDS:=+wprobe-info
   TITLE:=Wireless measurement data exporter
 endef
 
@@ -113,8 +113,9 @@ define Package/wprobe-info/install
 endef
 
 define Package/wprobe-export/install
-	$(INSTALL_DIR) $(1)/sbin $(1)/etc/init.d
+	$(INSTALL_DIR) $(1)/sbin $(1)/etc/init.d $(1)/etc/config
 	$(INSTALL_BIN) ./files/wprobe.init $(1)/etc/init.d/
+	$(INSTALL_BIN) ./files/wprobe.config $(1)/etc/config/wprobe
 	$(INSTALL_BIN) $(PKG_BUILD_DIR)/exporter/wprobe-export $(1)/sbin/
 endef
 
diff --git a/package/wprobe/files/wprobe.config b/package/wprobe/files/wprobe.config
new file mode 100644
index 0000000..8494bcc
--- /dev/null
+++ b/package/wprobe/files/wprobe.config
@@ -0,0 +1,7 @@
+config export
+	# uncomment this line to enable ipfix export:
+	# option type ipfix
+	option ifname ath0
+	option host ipfix-col
+	option proto tcp
+
diff --git a/package/wprobe/files/wprobe.init b/package/wprobe/files/wprobe.init
index 3c62a03..cf0b162 100755
--- a/package/wprobe/files/wprobe.init
+++ b/package/wprobe/files/wprobe.init
@@ -1,10 +1,11 @@
 #!/bin/sh /etc/rc.common
 START=90
+EXPORTER=/usr/sbin/wprobe-ipfix
 
 wprobe_ssd() {
 	local cfg="$1"; shift
 	local cmd="$1"; shift
-	start-stop-daemon "$cmd" -p "/var/run/wprobe-$cfg.pid" -b -x /sbin/wprobe-export -m -- "$@"
+	start-stop-daemon "$cmd" -p "/var/run/wprobe-$cfg.pid" -b -x "$EXPORTER" -m -- "$@"
 }
 
 stop_wprobe() {
@@ -13,7 +14,14 @@ stop_wprobe() {
 	rm -f "/var/run/wprobe-$cfg.pid"
 }
 
-start_wprobe() {
+config_wprobe() {
+	config_get ifname "$cfg" ifname
+	config_get interval "$cfg" interval
+	[ -n "$interval" ] || interval=100
+	wprobe-info "$ifname" -c -i "$interval"
+}
+
+start_ipfix() {
 	local cfg="$1"
 	config_get ifname "$cfg" interface
 	config_get host "$cfg" host
@@ -29,9 +37,17 @@ start_wprobe() {
 		echo "wprobe-export: missing host or interface name in config $cfg"
 		return
 	}
+	config_wprobe "$cfg"
 	wprobe_ssd "$cfg" -S "$proto" -i "$ifname" -c "$host" -p "${port:-4739}"
 }
 
+start_export() {
+	config_get export_type "$cfg" type
+	case "$export_type" in 
+		ipfix) start_ipfix "$cfg";;
+	esac
+}
+
 stop() {
 	for f in /var/run/wprobe-*.pid; do
 		CFG="${f%%.pid}"
@@ -42,5 +58,6 @@ stop() {
 
 start() {
 	config_load wprobe
-	config_foreach start_wprobe wprobe
+	config_foreach config_wprobe interface
+	[ -x "$EXPORTER" ] && config_foreach start_export export
 }
diff --git a/package/wprobe/src/exporter/wprobe-export.c b/package/wprobe/src/exporter/wprobe-export.c
index e9aa3de..fa32e8b 100644
--- a/package/wprobe/src/exporter/wprobe-export.c
+++ b/package/wprobe/src/exporter/wprobe-export.c
@@ -65,8 +65,8 @@ static struct wprobe_mapping map_globals[] = {
 };
 
 static struct wprobe_mapping map_perlink[] = {
-	WMAP(IEEE_TX_RATE, "tx_rate", .scale = 10.0f),
-	WMAP(IEEE_RX_RATE, "rx_rate", .scale = 10.0f),
+	WMAP(IEEE_TX_RATE, "tx_rate"),
+	WMAP(IEEE_RX_RATE, "rx_rate"),
 	WMAP(RSSI, "rssi"),
 	WMAP(SIGNAL, "signal"),
 	WMAP(RETRANSMIT_200, "retransmit_200"),
@@ -77,9 +77,6 @@ static struct wprobe_mapping map_perlink[] = {
 
 static unsigned char link_local[6];
 static char link_default[6];
-static LIST_HEAD(global_attr);
-static LIST_HEAD(link_attr);
-static LIST_HEAD(links);
 static int nfields = 0;
 
 #define FOKUS_USERID	12325
@@ -166,20 +163,20 @@ add_template_fields(ipfix_t *handle, ipfix_template_t *t, struct wprobe_mapping
 }
 
 static void
-wprobe_dump_data(ipfix_t *ipfixh, ipfix_template_t *ipfixt, const char *ifname, struct list_head *gl, struct list_head *ll, struct list_head *ls)
+wprobe_dump_data(ipfix_t *ipfixh, ipfix_template_t *ipfixt, struct wprobe_iface *dev)
 {
 	struct wprobe_link *link;
 
-	wprobe_update_links(ifname, ls);
-	wprobe_request_data(ifname, gl, NULL, 2);
-	if (list_empty(ls)) {
+	wprobe_update_links(dev);
+	wprobe_request_data(dev, NULL);
+	if (list_empty(&dev->links)) {
 		g_data.addrs[1] = link_default;
 		ipfix_export_array(ipfixh, ipfixt, g_data.maxfields, g_data.addrs, g_data.lens);
 		ipfix_export_flush(ipfixh);
 	}
-	list_for_each_entry(link, ls, list) {
+	list_for_each_entry(link, &dev->links, list) {
 		g_data.addrs[1] = link->addr;
-		wprobe_request_data(ifname, ll, link->addr, 2);
+		wprobe_request_data(dev, link->addr);
 		ipfix_export_array(ipfixh, ipfixt, g_data.maxfields, g_data.addrs, g_data.lens);
 		ipfix_export_flush(ipfixh);
 	}
@@ -187,6 +184,7 @@ wprobe_dump_data(ipfix_t *ipfixh, ipfix_template_t *ipfixt, const char *ifname,
 
 int main ( int argc, char **argv )
 {
+	struct wprobe_iface *dev = NULL;
     ipfix_template_t  *ipfixt = NULL;
     ipfix_t *ipfixh = NULL;
     int protocol = IPFIX_PROTO_TCP;
@@ -254,20 +252,14 @@ int main ( int argc, char **argv )
 		return -1;
 	}
 
-	if (wprobe_init() != 0) {
-		fprintf(stderr, "wprobe init failed\n");
-		return -1;
-	}
-
-	wprobe_dump_attributes(ifname, false, &global_attr, (char *) link_local);
-	wprobe_dump_attributes(ifname, true, &link_attr, NULL);
-	if (list_empty(&global_attr) && list_empty(&link_attr)) {
+	dev = wprobe_get_dev(ifname);
+	if (!dev || (list_empty(&dev->global_attr) && list_empty(&dev->link_attr))) {
 		fprintf(stderr, "Cannot connect to wprobe on interface '%s'\n", ifname);
 		return -1;
 	}
 
-	match_template(map_globals, ARRAY_SIZE(map_globals), &global_attr);
-	match_template(map_perlink, ARRAY_SIZE(map_perlink), &link_attr);
+	match_template(map_globals, ARRAY_SIZE(map_globals), &dev->global_attr);
+	match_template(map_perlink, ARRAY_SIZE(map_perlink), &dev->link_attr);
 	if (nfields == 0) {
 		fprintf(stderr, "No usable attributes found\n");
 		return -1;
@@ -300,14 +292,8 @@ int main ( int argc, char **argv )
 	add_template_fields(ipfixh, ipfixt, map_perlink, ARRAY_SIZE(map_perlink));
 
 	while (!do_close) {
-		usleep(100 * 1000);
-		wprobe_measure(ifname);
-
-		if (i-- > 0)
-			continue;
-
-		i = 10;
-		wprobe_dump_data(ipfixh, ipfixt, ifname, &global_attr, &link_attr, &links);
+		sleep(1);
+		wprobe_dump_data(ipfixh, ipfixt, dev);
     }
 
     ipfix_delete_template( ipfixh, ipfixt );
diff --git a/package/wprobe/src/kernel/linux/wprobe.h b/package/wprobe/src/kernel/linux/wprobe.h
index f145195..42bfbd0 100644
--- a/package/wprobe/src/kernel/linux/wprobe.h
+++ b/package/wprobe/src/kernel/linux/wprobe.h
@@ -32,13 +32,12 @@
  *
  * @WPROBE_ATTR_INTERFACE: interface name to process query on (NLA_STRING)
  * @WPROBE_ATTR_MAC: mac address (used for wireless links) (NLA_STRING)
- * @WPROBE_ATTR_FLAGS: interface/link/attribute flags (see enum wprobe_flags) (NLA_U32)
- * @WPROBE_ATTR_DURATION: sampling duration (in milliseconds) (NLA_MSECS)
+ * @WPROBE_ATTR_FLAGS: interface/link/attribute flags (see enum wprobe_flags) (NLA_U32)a
+ * @WPROBE_ATTR_DURATION: sampling duration (in milliseconds) (NLA_MSECS) 
  *
  * @WPROBE_ATTR_ID: attribute id (NLA_U32)
  * @WPROBE_ATTR_NAME: attribute name (NLA_STRING)
  * @WPROBE_ATTR_TYPE: attribute type (NLA_U8)
- * @WPROBE_ATTR_SCALE: attribute scale factor (NLA_U32)
  *
  * attribute values:
  *
@@ -56,22 +55,29 @@
  * @WPROBE_VAL_SUM: sum of all samples
  * @WPROBE_VAL_SUM_SQ: sum of all samples^2
  * @WPROBE_VAL_SAMPLES: number of samples
+ * @WPROBE_VAL_SCALE_TIME: last time the samples were scaled down
+ *
+ * configuration:
+ * @WPROBE_ATTR_INTERVAL: (measurement interval in milliseconds) (NLA_MSECS)
+ * @WPROBE_ATTR_SAMPLES_MIN: minimum samples to keep during inactivity (NLA_U32)
+ * @WPROBE_ATTR_SAMPLES_MAX: maximum samples to keep before scaling down (NLA_U32)
+ * @WPROBE_ATTR_SAMPLES_SCALE_M: multiplier for scaling down samples (NLA_U32)
+ * @WPROBE_ATTR_SAMPLES_SCALE_D: divisor for scaling down samples (NLA_U32)
  *
  * @WPROBE_ATTR_LAST: unused
  */
 enum wprobe_attr {
+	/* query attributes */
 	WPROBE_ATTR_UNSPEC,
 	WPROBE_ATTR_INTERFACE,
 	WPROBE_ATTR_MAC,
 	WPROBE_ATTR_FLAGS,
-	WPROBE_ATTR_DURATION,
-	WPROBE_ATTR_SCALE,
-	/* end of query attributes */
 
 	/* response data */
 	WPROBE_ATTR_ID,
 	WPROBE_ATTR_NAME,
 	WPROBE_ATTR_TYPE,
+	WPROBE_ATTR_DURATION,
 
 	/* value type attributes */
 	WPROBE_VAL_STRING,
@@ -88,6 +94,14 @@ enum wprobe_attr {
 	WPROBE_VAL_SUM,
 	WPROBE_VAL_SUM_SQ,
 	WPROBE_VAL_SAMPLES,
+	WPROBE_VAL_SCALE_TIME,
+
+	/* config attributes */
+	WPROBE_ATTR_INTERVAL,
+	WPROBE_ATTR_SAMPLES_MIN,
+	WPROBE_ATTR_SAMPLES_MAX,
+	WPROBE_ATTR_SAMPLES_SCALE_M,
+	WPROBE_ATTR_SAMPLES_SCALE_D,
 
 	WPROBE_ATTR_LAST
 };
@@ -117,6 +131,7 @@ enum wprobe_cmd {
 	WPROBE_CMD_SET_FLAGS,
 	WPROBE_CMD_MEASURE,
 	WPROBE_CMD_GET_LINKS,
+	WPROBE_CMD_CONFIG,
 	WPROBE_CMD_LAST
 };
 
@@ -192,6 +207,7 @@ struct wprobe_value {
 
 	/* timestamps */
 	u64 first, last;
+	u64 scale_timestamp;
 };
 
 /**
@@ -225,7 +241,8 @@ struct wprobe_iface {
 	const struct wprobe_item *global_items;
 	int n_global_items;
 
-	int (*sync_data)(struct wprobe_iface *dev, struct wprobe_link *l, struct wprobe_value *val, bool measure);
+	int (*sync_data)(struct wprobe_iface *dev, struct wprobe_link *l,
+	                 struct wprobe_value *val, bool measure);
 	void *priv;
 
 	/* handled by the wprobe core */
@@ -234,6 +251,14 @@ struct wprobe_iface {
 	spinlock_t lock;
 	void *val;
 	void *query_val;
+
+	u32 measure_interval;
+	struct timer_list measure_timer;
+
+	u32 scale_min;
+	u32 scale_max;
+	u32 scale_m;
+	u32 scale_d;
 };
 
 #define WPROBE_FILL_BEGIN(_ptr, _list) do {			\
diff --git a/package/wprobe/src/kernel/wprobe-core.c b/package/wprobe/src/kernel/wprobe-core.c
index 798cd7d..51ee7bc 100644
--- a/package/wprobe/src/kernel/wprobe-core.c
+++ b/package/wprobe/src/kernel/wprobe-core.c
@@ -34,6 +34,8 @@
 #define list_for_each_rcu __list_for_each_rcu
 #endif
 
+#define WPROBE_MIN_INTERVAL		100 /* minimum measurement interval in msecs */
+
 static struct list_head wprobe_if;
 static spinlock_t wprobe_lock;
 
@@ -43,10 +45,11 @@ static struct genl_family wprobe_fam = {
 	.hdrsize = 0,
 	.version = 1,
 	/* only the first set of attributes is used for queries */
-	.maxattr = WPROBE_ATTR_ID,
+	.maxattr = WPROBE_ATTR_LAST,
 };
 
 static void wprobe_update_stats(struct wprobe_iface *dev, struct wprobe_link *l);
+static int wprobe_sync_data(struct wprobe_iface *dev, struct wprobe_link *l, bool query);
 
 int
 wprobe_add_link(struct wprobe_iface *s, struct wprobe_link *l, const char *addr)
@@ -81,6 +84,19 @@ wprobe_remove_link(struct wprobe_iface *s, struct wprobe_link *l)
 }
 EXPORT_SYMBOL(wprobe_remove_link);
 
+static void
+wprobe_measure_timer(unsigned long data)
+{
+	struct wprobe_iface *dev = (struct wprobe_iface *) data;
+
+	/* set next measurement interval */
+	mod_timer(&dev->measure_timer, jiffies +
+		msecs_to_jiffies(dev->measure_interval));
+
+	/* perform measurement */
+	wprobe_sync_data(dev, NULL, false);
+}
+
 int
 wprobe_add_iface(struct wprobe_iface *s)
 {
@@ -93,6 +109,7 @@ wprobe_add_iface(struct wprobe_iface *s)
 	BUG_ON(!s->name);
 	INIT_LIST_HEAD(&s->list);
 	INIT_LIST_HEAD(&s->links);
+	setup_timer(&s->measure_timer, wprobe_measure_timer, (unsigned long) s);
 
 	vsize = max(s->n_link_items, s->n_global_items);
 	s->val = kzalloc(sizeof(struct wprobe_value) * vsize, GFP_ATOMIC);
@@ -103,6 +120,15 @@ wprobe_add_iface(struct wprobe_iface *s)
 	if (!s->query_val)
 		goto error;
 
+	/* initialize defaults to be able to handle overflow,
+	 * user space will need to handle this if it keeps an
+	 * internal histogram */
+	s->scale_min = 20;
+	s->scale_max = (1 << 31);
+
+	s->scale_m = 1;
+	s->scale_d = 10;
+
 	spin_lock_irqsave(&wprobe_lock, flags);
 	list_add_rcu(&s->list, &wprobe_if);
 	spin_unlock_irqrestore(&wprobe_lock, flags);
@@ -123,6 +149,7 @@ wprobe_remove_iface(struct wprobe_iface *s)
 
 	BUG_ON(!list_empty(&s->links));
 
+	del_timer_sync(&s->measure_timer);
 	spin_lock_irqsave(&wprobe_lock, flags);
 	list_del_rcu(&s->list);
 	spin_unlock_irqrestore(&wprobe_lock, flags);
@@ -160,7 +187,7 @@ wprobe_get_dev(struct nlattr *attr)
 	return dev;
 }
 
-int
+static int
 wprobe_sync_data(struct wprobe_iface *dev, struct wprobe_link *l, bool query)
 {
 	struct wprobe_value *val;
@@ -190,11 +217,40 @@ done:
 }
 EXPORT_SYMBOL(wprobe_sync_data);
 
+static void
+wprobe_scale_stats(struct wprobe_iface *dev, const struct wprobe_item *item,
+                   struct wprobe_value *val, int n)
+{
+	u64 scale_ts = jiffies_64;
+	int i;
+
+	for (i = 0; i < n; i++) {
+		if (!(item[i].flags & WPROBE_F_KEEPSTAT))
+			continue;
+
+		if (val[i].n <= dev->scale_min)
+			continue;
+
+		/* FIXME: div_s64 seems to be very imprecise here, even when
+		 * the values are scaled up */
+		val[i].s *= dev->scale_m;
+		val[i].s = div_s64(val[i].s, dev->scale_d);
+
+		val[i].ss *= dev->scale_m;
+		val[i].ss = div_s64(val[i].ss, dev->scale_d);
+
+		val[i].n = (val[i].n * dev->scale_m) / dev->scale_d;
+		val[i].scale_timestamp = scale_ts;
+	}
+}
+
+
 void
 wprobe_update_stats(struct wprobe_iface *dev, struct wprobe_link *l)
 {
 	const struct wprobe_item *item;
 	struct wprobe_value *val;
+	bool scale_stats = false;
 	int i, n;
 
 	if (l) {
@@ -215,6 +271,10 @@ wprobe_update_stats(struct wprobe_iface *dev, struct wprobe_link *l)
 			continue;
 
 		val[i].n++;
+		if ((item[i].flags & WPROBE_F_KEEPSTAT) &&
+			(dev->scale_max > 0) && (val[i].n > dev->scale_max)) {
+			scale_stats = true;
+		}
 
 		switch(item[i].type) {
 		case WPROBE_VAL_S8:
@@ -249,15 +309,22 @@ wprobe_update_stats(struct wprobe_iface *dev, struct wprobe_link *l)
 		val[i].ss += v * v;
 		val[i].pending = false;
 	}
+	if (scale_stats)
+		wprobe_scale_stats(dev, item, val, n);
 }
 EXPORT_SYMBOL(wprobe_update_stats);
 
-static const struct nla_policy wprobe_policy[WPROBE_ATTR_ID+1] = {
+static const struct nla_policy wprobe_policy[WPROBE_ATTR_LAST+1] = {
 	[WPROBE_ATTR_INTERFACE] = { .type = NLA_NUL_STRING },
 	[WPROBE_ATTR_MAC] = { .type = NLA_STRING },
-	[WPROBE_ATTR_DURATION] = { .type = NLA_MSECS },
 	[WPROBE_ATTR_FLAGS] = { .type = NLA_U32 },
-	[WPROBE_ATTR_SCALE] = { .type = NLA_U32 },
+
+	/* config */
+	[WPROBE_ATTR_INTERVAL] = { .type = NLA_MSECS },
+	[WPROBE_ATTR_SAMPLES_MIN] = { .type = NLA_U32 },
+	[WPROBE_ATTR_SAMPLES_MAX] = { .type = NLA_U32 },
+	[WPROBE_ATTR_SAMPLES_SCALE_M] = { .type = NLA_U32 },
+	[WPROBE_ATTR_SAMPLES_SCALE_D] = { .type = NLA_U32 },
 };
 
 static bool
@@ -322,6 +389,7 @@ wprobe_send_item_value(struct sk_buff *msg, struct netlink_callback *cb,
 		NLA_PUT_U64(msg, WPROBE_VAL_SUM, val[i].s);
 		NLA_PUT_U64(msg, WPROBE_VAL_SUM_SQ, val[i].ss);
 		NLA_PUT_U32(msg, WPROBE_VAL_SAMPLES, (u32) val[i].n);
+		NLA_PUT_MSECS(msg, WPROBE_VAL_SCALE_TIME, val[i].scale_timestamp);
 	}
 done:
 	genlmsg_end(msg, hdr);
@@ -432,29 +500,6 @@ wprobe_dump_links(struct sk_buff *skb, struct netlink_callback *cb)
 done:
 	return err;
 }
-static void
-wprobe_scale_stats(const struct wprobe_item *item, struct wprobe_value *val, int n, u32 flags)
-{
-	u32 scale = 0;
-	int i;
-
-	for (i = 0; i < n; i++) {
-		if (!(item[i].flags & WPROBE_F_KEEPSTAT))
-			continue;
-
-		/* reset statistics, if requested */
-		if (flags & WPROBE_F_RESET)
-			scale = val[i].n;
-		else if (wprobe_fam.attrbuf[WPROBE_ATTR_SCALE])
-			scale = nla_get_u32(wprobe_fam.attrbuf[WPROBE_ATTR_SCALE]);
-
-		if ((scale > 0) && (val[i].n > scale)) {
-			val[i].s = div_s64(val[i].s, scale);
-			val[i].ss = div_s64(val[i].ss, scale);
-			val[i].n = val[i].n / scale + 1;
-		}
-	}
-}
 
 #define WPROBE_F_LINK (1 << 31) /* for internal use */
 static int
@@ -515,7 +560,6 @@ wprobe_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 			err = wprobe_sync_data(dev, l, true);
 			if (!err)
 				memcpy(dev->query_val, val, n * sizeof(struct wprobe_value));
-			wprobe_scale_stats(item, val, n, flags);
 			spin_unlock_irqrestore(&dev->lock, flags);
 
 			if (err)
@@ -583,6 +627,25 @@ done:
 #undef WPROBE_F_LINK
 
 static int
+wprobe_update_auto_measurement(struct wprobe_iface *dev, u32 interval)
+{
+	if (interval && (interval < WPROBE_MIN_INTERVAL))
+		return -EINVAL;
+
+	if (!interval && dev->measure_interval)
+		del_timer_sync(&dev->measure_timer);
+
+	dev->measure_interval = interval;
+	if (!interval)
+		return 0;
+
+	/* kick of a new measurement immediately */
+	mod_timer(&dev->measure_timer, jiffies + 1);
+
+	return 0;
+}
+
+static int
 wprobe_measure(struct sk_buff *skb, struct genl_info *info)
 {
 	struct wprobe_iface *dev;
@@ -607,6 +670,75 @@ done:
 	return err;
 }
 
+static int
+wprobe_set_config(struct sk_buff *skb, struct genl_info *info)
+{
+	struct wprobe_iface *dev;
+	unsigned long flags;
+	int err = -ENOENT;
+	u32 scale_min, scale_max;
+	u32 scale_m, scale_d;
+
+	rcu_read_lock();
+	dev = wprobe_get_dev(info->attrs[WPROBE_ATTR_INTERFACE]);
+	if (!dev)
+		goto done_unlocked;
+
+	err = -EINVAL;
+	spin_lock_irqsave(&dev->lock, flags);
+	if (info->attrs[WPROBE_ATTR_MAC]) {
+		/* not supported yet */
+		goto done;
+	}
+
+	if (info->attrs[WPROBE_ATTR_SAMPLES_MIN] ||
+		info->attrs[WPROBE_ATTR_SAMPLES_MAX]) {
+		if (info->attrs[WPROBE_ATTR_SAMPLES_MIN])
+			scale_min = nla_get_u32(info->attrs[WPROBE_ATTR_SAMPLES_MIN]);
+		else
+			scale_min = dev->scale_min;
+
+		if (info->attrs[WPROBE_ATTR_SAMPLES_MAX])
+			scale_max = nla_get_u32(info->attrs[WPROBE_ATTR_SAMPLES_MAX]);
+		else
+			scale_max = dev->scale_max;
+
+		if ((!scale_min && !scale_max) ||
+		    (scale_min && scale_max && (scale_min < scale_max))) {
+			dev->scale_min = scale_min;
+			dev->scale_max = scale_max;
+		} else {
+			goto done;
+		}
+	}
+
+	if (info->attrs[WPROBE_ATTR_SAMPLES_SCALE_M] &&
+		info->attrs[WPROBE_ATTR_SAMPLES_SCALE_D]) {
+
+		scale_m = nla_get_u32(info->attrs[WPROBE_ATTR_SAMPLES_SCALE_M]);
+		scale_d = nla_get_u32(info->attrs[WPROBE_ATTR_SAMPLES_SCALE_D]);
+
+		if (!scale_d || (scale_m > scale_d))
+			goto done;
+
+		dev->scale_m = scale_m;
+		dev->scale_d = scale_d;
+	}
+
+	err = 0;
+	if (info->attrs[WPROBE_ATTR_INTERVAL]) {
+		/* change of measurement interval requested */
+		err = wprobe_update_auto_measurement(dev,
+			(u32) nla_get_u64(info->attrs[WPROBE_ATTR_INTERVAL]));
+	}
+
+done:
+	spin_unlock_irqrestore(&dev->lock, flags);
+done_unlocked:
+	rcu_read_unlock();
+	return err;
+}
+
 static struct genl_ops wprobe_ops[] = {
 	{
 		.cmd = WPROBE_CMD_GET_INFO,
@@ -627,7 +759,11 @@ static struct genl_ops wprobe_ops[] = {
 		.cmd = WPROBE_CMD_GET_LINKS,
 		.dumpit = wprobe_dump_links,
 		.policy = wprobe_policy,
-	}
+	},
+	{
+		.cmd = WPROBE_CMD_CONFIG,
+		.doit = wprobe_set_config,
+	},
 };
 
 static void __exit
diff --git a/package/wprobe/src/user/wprobe-info.c b/package/wprobe/src/user/wprobe-info.c
index b891871..8361c02 100644
--- a/package/wprobe/src/user/wprobe-info.c
+++ b/package/wprobe/src/user/wprobe-info.c
@@ -64,15 +64,15 @@ wprobe_dump_value(struct wprobe_attribute *attr)
 
 
 static void
-wprobe_dump_data(const char *ifname, struct list_head *gl, struct list_head *ll, struct list_head *ls)
+wprobe_dump_data(struct wprobe_iface *dev)
 {
 	struct wprobe_attribute *attr;
 	struct wprobe_link *link;
 	bool first = true;
 
 	fprintf(stderr, "\n");
-	wprobe_request_data(ifname, gl, NULL, 2);
-	list_for_each_entry(attr, gl, list) {
+	wprobe_request_data(dev, NULL);
+	list_for_each_entry(attr, &dev->global_attr, list) {
 		fprintf(stderr, (first ?
 			"Global:            %s=%s\n" :
 			"                   %s=%s\n"),
@@ -82,10 +82,10 @@ wprobe_dump_data(const char *ifname, struct list_head *gl, struct list_head *ll,
 		first = false;
 	}
 
-	list_for_each_entry(link, ls, list) {
+	list_for_each_entry(link, &dev->links, list) {
 		first = true;
-		wprobe_request_data(ifname, ll, link->addr, 2);
-		list_for_each_entry(attr, ll, list) {
+		wprobe_request_data(dev, link->addr);
+		list_for_each_entry(attr, &dev->link_attr, list) {
 			if (first) {
 				fprintf(stderr,
 					"%02x:%02x:%02x:%02x:%02x:%02x: %s=%s\n",
@@ -119,57 +119,92 @@ static const char *attr_typestr[] = {
 
 static int usage(const char *prog)
 {
-	fprintf(stderr, "Usage: %s <interface>\n", prog);
-	return 1;
+	fprintf(stderr,
+		"Usage: %s <interface> [options]\n"
+		"\n"
+		"Options:\n"
+		"  -c:            Only apply configuration\n"
+		"  -h:            This help text\n"
+		"  -i <interval>: Set measurement interval\n"
+		"  -m:            Run measurement loop\n"
+		"\n"
+		, prog);
+	exit(1);
 }
 
-int main(int argc, char **argv)
+static void show_attributes(struct wprobe_iface *dev)
 {
 	struct wprobe_attribute *attr;
-	const char *ifname;
-	LIST_HEAD(global_attr);
-	LIST_HEAD(link_attr);
-	LIST_HEAD(links);
-	int i = 0;
+	list_for_each_entry(attr, &dev->global_attr, list) {
+		fprintf(stderr, "Global attribute: '%s' (%s)\n",
+			attr->name, attr_typestr[attr->type]);
+	}
+	list_for_each_entry(attr, &dev->link_attr, list) {
+		fprintf(stderr, "Link attribute: '%s' (%s)\n",
+			attr->name, attr_typestr[attr->type]);
+	}
+}
 
-	if (argc < 2)
-		return usage(argv[0]);
+static void loop_measurement(struct wprobe_iface *dev)
+{
+	while (1) {
+		sleep(1);
+		wprobe_update_links(dev);
+		wprobe_dump_data(dev);
+	}
+}
 
-	ifname = argv[1];
+int main(int argc, char **argv)
+{
+	struct wprobe_iface *dev;
+	const char *ifname;
+	const char *prog = argv[0];
+	enum {
+		CMD_NONE,
+		CMD_CONFIG,
+		CMD_MEASURE,
+	} cmd = CMD_NONE;
+	int ch;
 
-	if (wprobe_init() != 0)
-		return -1;
+	if ((argc < 2) || (argv[1][0] == '-'))
+		return usage(prog);
 
-	wprobe_dump_attributes(ifname, false, &global_attr, NULL);
-	wprobe_dump_attributes(ifname, true, &link_attr, NULL);
+	ifname = argv[1];
+	dev = wprobe_get_dev(ifname);
+	argv++;
+	argc--;
 
-	if (list_empty(&global_attr) &&
-		list_empty(&link_attr)) {
+	if (!dev || (list_empty(&dev->global_attr) &&
+		list_empty(&dev->link_attr))) {
 		fprintf(stderr, "Interface '%s' not found\n", ifname);
 		return -1;
 	}
 
-	list_for_each_entry(attr, &global_attr, list) {
-		fprintf(stderr, "Global attribute: '%s' (%s)\n",
-			attr->name, attr_typestr[attr->type]);
-	}
-	list_for_each_entry(attr, &link_attr, list) {
-		fprintf(stderr, "Link attribute: '%s' (%s)\n",
-			attr->name, attr_typestr[attr->type]);
+	while ((ch = getopt(argc, argv, "chi:m")) != -1) {
+		switch(ch) {
+		case 'c':
+			cmd = CMD_CONFIG;
+			break;
+		case 'm':
+			cmd = CMD_MEASURE;
+			break;
+		case 'i':
+			dev->interval = strtoul(optarg, NULL, 10);
+			break;
+		case 'h':
+		default:
+			usage(prog);
+			break;
+		}
 	}
 
-	while (1) {
-		usleep(100 * 1000);
-		wprobe_measure(ifname);
-
-		if (i-- > 0)
-			continue;
+	wprobe_apply_config(dev);
+	if (cmd != CMD_CONFIG)
+		show_attributes(dev);
+	if (cmd == CMD_MEASURE)
+		loop_measurement(dev);
 
-		i = 10;
-		wprobe_update_links(ifname, &links);
-		wprobe_dump_data(ifname, &global_attr, &link_attr, &links);
-	}
-	wprobe_free();
+	wprobe_free_dev(dev);
 
 	return 0;
 }
diff --git a/package/wprobe/src/user/wprobe.c b/package/wprobe/src/user/wprobe.c
index 1f8df6c..e48f768 100644
--- a/package/wprobe/src/user/wprobe.c
+++ b/package/wprobe/src/user/wprobe.c
@@ -35,6 +35,7 @@
 #define DPRINTF(fmt, ...) do {} while (0)
 #endif
 
+static int n_devs = 0;
 static struct nl_sock *handle = NULL;
 static struct nl_cache *cache = NULL;
 static struct genl_family *family = NULL;
@@ -83,9 +84,16 @@ ack_handler(struct nl_msg *msg, void *arg)
 }
 
 
-void
+static void
 wprobe_free(void)
 {
+	/* should not happen */
+	if (n_devs == 0)
+		return;
+
+	if (--n_devs != 0)
+		return;
+
 	if (cache)
 		nl_cache_free(cache);
 	if (handle)
@@ -94,11 +102,14 @@ wprobe_free(void)
 	cache = NULL;
 }
 
-int
+static int
 wprobe_init(void)
 {
 	int ret;
 
+	if (n_devs++ > 0)
+		return 0;
+
 	handle = nl_socket_alloc();
 	if (!handle) {
 		DPRINTF("Failed to create handle\n");
@@ -233,8 +244,8 @@ save_attribute_handler(struct nl_msg *msg, void *arg)
 }
 
 
-int
-wprobe_dump_attributes(const char *ifname, bool link, struct list_head *list, char *addr)
+static int
+dump_attributes(const char *ifname, bool link, struct list_head *list, char *addr)
 {
 	struct nl_msg *msg;
 	struct wprobe_attr_cb cb;
@@ -255,6 +266,64 @@ nla_put_failure:
 	return -EINVAL;
 }
 
+struct wprobe_iface *
+wprobe_get_dev(const char *ifname)
+{
+	struct wprobe_iface *dev;
+
+	if (wprobe_init() != 0)
+		return NULL;
+
+	dev = malloc(sizeof(struct wprobe_iface));
+	if (!dev)
+		return NULL;
+
+	memset(dev, 0, sizeof(struct wprobe_iface));
+	dev->ifname = strdup(ifname);
+	if (!dev->ifname)
+		goto error;
+
+	dev->interval = -1;
+	dev->scale_min = -1;
+	dev->scale_max = -1;
+	dev->scale_m = -1;
+	dev->scale_d = -1;
+
+	INIT_LIST_HEAD(&dev->global_attr);
+	INIT_LIST_HEAD(&dev->link_attr);
+	INIT_LIST_HEAD(&dev->links);
+
+	dump_attributes(ifname, false, &dev->global_attr, NULL);
+	dump_attributes(ifname, true, &dev->link_attr, NULL);
+
+	return dev;
+
+error:
+	free(dev);
+	return NULL;
+}
+
+static void
+free_attr_list(struct list_head *list)
+{
+	struct wprobe_attribute *attr, *tmp;
+
+	list_for_each_entry_safe(attr, tmp, list, list) {
+		list_del(&attr->list);
+		free(attr);
+	}
+}
+
+void
+wprobe_free_dev(struct wprobe_iface *dev)
+{
+	wprobe_free();
+	free_attr_list(&dev->global_attr);
+	free_attr_list(&dev->link_attr);
+	free((void *)dev->ifname);
+	free(dev);
+}
+
 static struct wprobe_link *
 get_link(struct list_head *list, const char *addr)
 {
@@ -313,7 +382,7 @@ save_link_handler(struct nl_msg *msg, void *arg)
 
 
 int
-wprobe_update_links(const char *ifname, struct list_head *list)
+wprobe_update_links(struct wprobe_iface *dev)
 {
 	struct wprobe_link *l, *tmp;
 	struct nl_msg *msg;
@@ -321,10 +390,10 @@ wprobe_update_links(const char *ifname, struct list_head *list)
 	int err;
 
 	INIT_LIST_HEAD(&cb.old_list);
-	list_splice_init(list, &cb.old_list);
-	cb.list = list;
+	list_splice_init(&dev->links, &cb.old_list);
+	cb.list = &dev->links;
 
-	msg = wprobe_new_msg(ifname, WPROBE_CMD_GET_LINKS, true);
+	msg = wprobe_new_msg(dev->ifname, WPROBE_CMD_GET_LINKS, true);
 	if (!msg)
 		return -ENOMEM;
 
@@ -340,16 +409,37 @@ wprobe_update_links(const char *ifname, struct list_head *list)
 	return 0;
 }
 
-void
-wprobe_measure(const char *ifname)
+int
+wprobe_apply_config(struct wprobe_iface *dev)
 {
 	struct nl_msg *msg;
 
-	msg = wprobe_new_msg(ifname, WPROBE_CMD_MEASURE, false);
+	msg = wprobe_new_msg(dev->ifname, WPROBE_CMD_CONFIG, false);
 	if (!msg)
-		return;
+		return -ENOMEM;
+
+	if (dev->interval >= 0)
+		NLA_PUT_MSECS(msg, WPROBE_ATTR_INTERVAL, dev->interval);
+
+	wprobe_send_msg(msg, NULL, NULL);
+	return 0;
+
+nla_put_failure:
+	nlmsg_free(msg);
+	return -ENOMEM;
+}
+
+int
+wprobe_measure(struct wprobe_iface *dev)
+{
+	struct nl_msg *msg;
+
+	msg = wprobe_new_msg(dev->ifname, WPROBE_CMD_MEASURE, false);
+	if (!msg)
+		return -ENOMEM;
 
 	wprobe_send_msg(msg, NULL, NULL);
+	return 0;
 }
 
 struct wprobe_request_cb {
@@ -431,6 +521,10 @@ found:
 		if (attr->val.n > 0) {
 			float avg = ((float) attr->val.s) / attr->val.n;
 			float stdev = sqrt((((float) attr->val.ss) / attr->val.n) - (avg * avg));
+			if (isnan(stdev))
+				stdev = 0.0f;
+			if (isnan(avg))
+				avg = 0.0f;
 			attr->val.avg = avg;
 			attr->val.stdev = stdev;
 		}
@@ -443,25 +537,24 @@ out:
 
 
 int
-wprobe_request_data(const char *ifname, struct list_head *attrs, const unsigned char *addr, int scale)
+wprobe_request_data(struct wprobe_iface *dev, const unsigned char *addr)
 {
 	struct wprobe_request_cb cb;
+	struct list_head *attrs;
 	struct nl_msg *msg;
 	int err;
 
-	msg = wprobe_new_msg(ifname, WPROBE_CMD_GET_INFO, true);
+	msg = wprobe_new_msg(dev->ifname, WPROBE_CMD_GET_INFO, true);
 	if (!msg)
 		return -ENOMEM;
 
-	if (scale < 0)
-		NLA_PUT_U32(msg, WPROBE_ATTR_FLAGS, WPROBE_F_RESET);
-	else if (scale > 0)
-		NLA_PUT_U32(msg, WPROBE_ATTR_SCALE, scale);
-
-	if (addr)
+	if (addr) {
+		attrs = &dev->link_attr;
 		NLA_PUT(msg, WPROBE_ATTR_MAC, 6, addr);
+	} else {
+		attrs = &dev->global_attr;
+	}
 
-nla_put_failure:
 	INIT_LIST_HEAD(&cb.old_list);
 	list_splice_init(attrs, &cb.old_list);
 	cb.list = attrs;
@@ -469,6 +562,10 @@ nla_put_failure:
 	err = wprobe_send_msg(msg, save_attrdata_handler, &cb);
 	list_splice(&cb.old_list, attrs->prev);
 	return err;
+
+nla_put_failure:
+	nlmsg_free(msg);
+	return -ENOMEM;
 }
 
 
diff --git a/package/wprobe/src/user/wprobe.h b/package/wprobe/src/user/wprobe.h
index e0c33fa..c0b4902 100644
--- a/package/wprobe/src/user/wprobe.h
+++ b/package/wprobe/src/user/wprobe.h
@@ -87,15 +87,21 @@ struct wprobe_link {
 	unsigned char addr[6];
 };
 
-/**
- * wprobe_init: initialize internal data structures and connect to the wprobe netlink api
- */
-extern int wprobe_init(void);
+struct wprobe_iface {
+	const char *ifname;
+	char addr[6];
 
-/**
- * wprobe_free: free all internally allocated data structures
- */
-extern void wprobe_free(void);
+	struct list_head global_attr;
+	struct list_head link_attr;
+	struct list_head links;
+
+	/* config */
+	int interval;
+	int scale_min;
+	int scale_max;
+	int scale_m;
+	int scale_d;
+};
 
 /**
  * wprobe_update_links: get a list of all link partners
@@ -105,7 +111,7 @@ extern void wprobe_free(void);
  * when wprobe_update_links is called multiple times, the linked list 
  * is updated with new link partners, old entries are automatically expired
  */
-extern int wprobe_update_links(const char *ifname, struct list_head *list);
+extern int wprobe_update_links(struct wprobe_iface *dev);
 
 /**
  * wprobe_measure: start a measurement request for all global attributes
@@ -115,29 +121,39 @@ extern int wprobe_update_links(const char *ifname, struct list_head *list);
  * it may be desirable to control the sampling interval from user space
  * you can use this function to do that.
  */
-extern void wprobe_measure(const char *ifname);
+extern int wprobe_measure(struct wprobe_iface *dev);
 
 /**
- * wprobe_dump_attributes: create a linked list of available attributes
+ * wprobe_get_dev: get device information
  * @ifname: name of the wprobe interface
- * @link: false: get the list of global attributes; true: get the list of per-link attributes
- * @list: linked list to store the attributes in
- * @addr: buffer to store the interface's mac address in (optional)
  *
- * attributes must be freed by the caller
+ * queries the wprobe interface for all attributes
+ * must be freed with wprobe_free_dev
+ */
+extern struct wprobe_iface *wprobe_get_dev(const char *ifname);
+
+/**
+ * wprobe_get_dev: free all device information
+ * @dev: wprobe device structure
+ */
+extern void wprobe_free_dev(struct wprobe_iface *dev);
+
+/**
+ * wprobe_apply_config: apply configuration data
+ * @dev: wprobe device structure
+ *
+ * uploads all configuration values from @dev that are not set to -1
  */
-extern int wprobe_dump_attributes(const char *ifname, bool link, struct list_head *list, char *addr);
+extern int wprobe_apply_config(struct wprobe_iface *dev);
 
 /**
  * wprobe_request_data: request new sampling values for the given list of attributes
- * @ifname: name of the wprobe interface
- * @attrs: attribute list
+ * @dev: wprobe device structure
  * @addr: (optional) mac address of the link partner
- * @scale: scale down values by a factor (scale < 0: reset statistics entirely)
  *
- * if addr is unset, attrs must point to the list of global attributes,
- * if addr is set, attrs must point to the list of per-link attributes
+ * if addr is unset, global values are stored in the global attributes list
+ * if addr is set, per-link values for the given address are stored in the link attributes list
  */
-extern int wprobe_request_data(const char *ifname, struct list_head *attrs, const unsigned char *addr, int scale);
+extern int wprobe_request_data(struct wprobe_iface *dev, const unsigned char *addr);
 
 #endif