xen-netback: enable user to unload netback module

This patch enables user to unload netback module, which is useful when user
wants to upgrade to a newer netback module without rebooting the host.

Netfront cannot handle netback removal event. As we cannot fix all possible
frontends we add module get / put along with vif get / put to avoid
mis-unloading of netback. To unload netback module, user needs to shutdown all
VMs or migrate them to another host or unplug all vifs before hand.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>¬
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/common.h

@@ -120,6 +120,7 @@ void xenvif_get(struct xenvif *vif);
 void xenvif_put(struct xenvif *vif);
 
 int xenvif_xenbus_init(void);
+void xenvif_xenbus_fini(void);
 
 int xenvif_schedulable(struct xenvif *vif);
 

drivers/net/xen-netback/interface.c

@@ -316,6 +316,8 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
 	if (vif->irq)
 		return 0;
 
+	__module_get(THIS_MODULE);
+
 	err = xen_netbk_map_frontend_rings(vif, tx_ring_ref, rx_ring_ref);
 	if (err < 0)
 		goto err;
@@ -343,6 +345,7 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
 err_unmap:
 	xen_netbk_unmap_frontend_rings(vif);
 err:
+	module_put(THIS_MODULE);
 	return err;
 }
 
@@ -360,18 +363,32 @@ void xenvif_carrier_off(struct xenvif *vif)
 
 void xenvif_disconnect(struct xenvif *vif)
 {
+	/* Disconnect funtion might get called by generic framework
+	 * even before vif connects, so we need to check if we really
+	 * need to do a module_put.
+	 */
+	int need_module_put = 0;
+
 	if (netif_carrier_ok(vif->dev))
 		xenvif_carrier_off(vif);
 
 	atomic_dec(&vif->refcnt);
 	wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
 
-	if (vif->irq)
+	if (vif->irq) {
 		unbind_from_irqhandler(vif->irq, vif);
+		/* vif->irq is valid, we had a module_get in
+		 * xenvif_connect.
+		 */
+		need_module_put = 1;
+	}
 
 	unregister_netdev(vif->dev);
 
 	xen_netbk_unmap_frontend_rings(vif);
 
 	free_netdev(vif->dev);
+
+	if (need_module_put)
+		module_put(THIS_MODULE);
 }

drivers/net/xen-netback/netback.c

@@ -1949,5 +1949,25 @@ failed_init:
 
 module_init(netback_init);
 
+static void __exit netback_fini(void)
+{
+	int i, j;
+
+	xenvif_xenbus_fini();
+
+	for (i = 0; i < xen_netbk_group_nr; i++) {
+		struct xen_netbk *netbk = &xen_netbk[i];
+		del_timer_sync(&netbk->net_timer);
+		kthread_stop(netbk->task);
+		for (j = 0; j < MAX_PENDING_REQS; j++) {
+			if (netbk->mmap_pages[i])
+				__free_page(netbk->mmap_pages[i]);
+		}
+	}
+
+	vfree(xen_netbk);
+}
+module_exit(netback_fini);
+
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("xen-backend:vif");

drivers/net/xen-netback/xenbus.c

@@ -485,3 +485,8 @@ int xenvif_xenbus_init(void)
 {
 	return xenbus_register_backend(&netback_driver);
 }
+
+void xenvif_xenbus_fini(void)
+{
+	return xenbus_unregister_driver(&netback_driver);
+}