xen-netback: making the bandwidth limiter runtime settable

With the current netback, the bandwidth limiter's parameters are only
settable during vif setup time.  This patch register a watch on them, and
thus makes them runtime changeable.

When the watch fires, the timer is reset.  The timer's mutex is used for
fencing the change.

Cc: Anthony Liguori <aliguori@amazon.com>
Signed-off-by: Imre Palik <imrep@amazon.de>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/common.h

@@ -238,6 +238,8 @@ struct xenvif {
 	unsigned int num_queues; /* active queues, resource allocated */
 	unsigned int stalled_queues;
 
+	struct xenbus_watch credit_watch;
+
 	spinlock_t lock;
 
 #ifdef CONFIG_DEBUG_FS
@@ -260,6 +262,8 @@ static inline struct xenbus_device *xenvif_to_xenbus_device(struct xenvif *vif)
 	return to_xenbus_device(vif->dev->dev.parent);
 }
 
+void xenvif_tx_credit_callback(unsigned long data);
+
 struct xenvif *xenvif_alloc(struct device *parent,
 			    domid_t domid,
 			    unsigned int handle);

drivers/net/xen-netback/interface.c

@@ -463,6 +463,7 @@ int xenvif_init_queue(struct xenvif_queue *queue)
 	queue->credit_bytes = queue->remaining_credit = ~0UL;
 	queue->credit_usec  = 0UL;
 	init_timer(&queue->credit_timeout);
+	queue->credit_timeout.function = xenvif_tx_credit_callback;
 	queue->credit_window_start = get_jiffies_64();
 
 	queue->rx_queue_max = XENVIF_RX_QUEUE_BYTES;

drivers/net/xen-netback/netback.c

@@ -641,7 +641,7 @@ static void tx_add_credit(struct xenvif_queue *queue)
 	queue->remaining_credit = min(max_credit, max_burst);
 }
 
-static void tx_credit_callback(unsigned long data)
+void xenvif_tx_credit_callback(unsigned long data)
 {
 	struct xenvif_queue *queue = (struct xenvif_queue *)data;
 	tx_add_credit(queue);
@@ -1169,8 +1169,6 @@ static bool tx_credit_exceeded(struct xenvif_queue *queue, unsigned size)
 	if (size > queue->remaining_credit) {
 		queue->credit_timeout.data     =
 			(unsigned long)queue;
-		queue->credit_timeout.function =
-			tx_credit_callback;
 		mod_timer(&queue->credit_timeout,
 			  next_credit);
 		queue->credit_window_start = next_credit;

drivers/net/xen-netback/xenbus.c

@@ -41,6 +41,7 @@ static void connect(struct backend_info *be);
 static int read_xenbus_vif_flags(struct backend_info *be);
 static int backend_create_xenvif(struct backend_info *be);
 static void unregister_hotplug_status_watch(struct backend_info *be);
+static void xen_unregister_watchers(struct xenvif *vif);
 static void set_backend_state(struct backend_info *be,
 			      enum xenbus_state state);
 
@@ -232,6 +233,7 @@ static int netback_remove(struct xenbus_device *dev)
 	unregister_hotplug_status_watch(be);
 	if (be->vif) {
 		kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
+		xen_unregister_watchers(be->vif);
 		xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
 		xenvif_free(be->vif);
 		be->vif = NULL;
@@ -430,6 +432,7 @@ static int backend_create_xenvif(struct backend_info *be)
 static void backend_disconnect(struct backend_info *be)
 {
 	if (be->vif) {
+		xen_unregister_watchers(be->vif);
 #ifdef CONFIG_DEBUG_FS
 		xenvif_debugfs_delif(be->vif);
 #endif /* CONFIG_DEBUG_FS */
@@ -645,6 +648,59 @@ static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
 	return 0;
 }
 
+static void xen_net_rate_changed(struct xenbus_watch *watch,
+				const char **vec, unsigned int len)
+{
+	struct xenvif *vif = container_of(watch, struct xenvif, credit_watch);
+	struct xenbus_device *dev = xenvif_to_xenbus_device(vif);
+	unsigned long   credit_bytes;
+	unsigned long   credit_usec;
+	unsigned int queue_index;
+
+	xen_net_read_rate(dev, &credit_bytes, &credit_usec);
+	for (queue_index = 0; queue_index < vif->num_queues; queue_index++) {
+		struct xenvif_queue *queue = &vif->queues[queue_index];
+
+		queue->credit_bytes = credit_bytes;
+		queue->credit_usec = credit_usec;
+		if (!mod_timer_pending(&queue->credit_timeout, jiffies) &&
+			queue->remaining_credit > queue->credit_bytes) {
+			queue->remaining_credit = queue->credit_bytes;
+		}
+	}
+}
+
+static int xen_register_watchers(struct xenbus_device *dev, struct xenvif *vif)
+{
+	int err = 0;
+	char *node;
+	unsigned maxlen = strlen(dev->nodename) + sizeof("/rate");
+
+	node = kmalloc(maxlen, GFP_KERNEL);
+	if (!node)
+		return -ENOMEM;
+	snprintf(node, maxlen, "%s/rate", dev->nodename);
+	vif->credit_watch.node = node;
+	vif->credit_watch.callback = xen_net_rate_changed;
+	err = register_xenbus_watch(&vif->credit_watch);
+	if (err) {
+		pr_err("Failed to set watcher %s\n", vif->credit_watch.node);
+		kfree(node);
+		vif->credit_watch.node = NULL;
+		vif->credit_watch.callback = NULL;
+	}
+	return err;
+}
+
+static void xen_unregister_watchers(struct xenvif *vif)
+{
+	if (vif->credit_watch.node) {
+		unregister_xenbus_watch(&vif->credit_watch);
+		kfree(vif->credit_watch.node);
+		vif->credit_watch.node = NULL;
+	}
+}
+
 static void unregister_hotplug_status_watch(struct backend_info *be)
 {
 	if (be->have_hotplug_status_watch) {
@@ -709,6 +765,7 @@ static void connect(struct backend_info *be)
 	}
 
 	xen_net_read_rate(dev, &credit_bytes, &credit_usec);
+	xen_register_watchers(dev, be->vif);
 	read_xenbus_vif_flags(be);
 
 	/* Use the number of queues requested by the frontend */