From dab88520d6ef96a5546d79ef1f12843df3cdf71a Mon Sep 17 00:00:00 2001
From: "K. Y. Srinivasan" <kys@microsoft.com>
Date: Thu, 1 Dec 2011 09:59:34 -0800
Subject: [PATCH] --- yaml --- r: 280055 b: refs/heads/master c:
 cf6a2eacbcb2593b5b91d0817915c4f0464bb534 h: refs/heads/master i:   280053:
 9353d036c1ab399583c41eecbb684f330691ea6d   280051:
 4871bebbcb2338d1819c98d9f3926090d2c1df9b   280047:
 58f4abaeeda4dabb405e6f086188d9026865a59b v: v3

---
 [refs]                       |  2 +-
 trunk/drivers/hv/vmbus_drv.c | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index 298c685eb9eb..78ab8920bfc6 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d2554f50df9be3c53a13f7541a5f4d054bd56cc3
+refs/heads/master: cf6a2eacbcb2593b5b91d0817915c4f0464bb534
diff --git a/trunk/drivers/hv/vmbus_drv.c b/trunk/drivers/hv/vmbus_drv.c
index 7d3bccb3b2a5..40956d1c6608 100644
--- a/trunk/drivers/hv/vmbus_drv.c
+++ b/trunk/drivers/hv/vmbus_drv.c
@@ -62,6 +62,14 @@ struct hv_device_info {
 	struct hv_dev_port_info outbound;
 };
 
+static int vmbus_exists(void)
+{
+	if (hv_acpi_dev == NULL)
+		return -ENODEV;
+
+	return 0;
+}
+
 
 static void get_channel_info(struct hv_device *device,
 			     struct hv_device_info *info)
@@ -590,6 +598,10 @@ int __vmbus_driver_register(struct hv_driver *hv_driver, struct module *owner, c
 
 	pr_info("registering driver %s\n", hv_driver->name);
 
+	ret = vmbus_exists();
+	if (ret < 0)
+		return ret;
+
 	hv_driver->driver.name = hv_driver->name;
 	hv_driver->driver.owner = owner;
 	hv_driver->driver.mod_name = mod_name;
@@ -614,6 +626,9 @@ void vmbus_driver_unregister(struct hv_driver *hv_driver)
 {
 	pr_info("unregistering driver %s\n", hv_driver->name);
 
+	if (!vmbus_exists())
+		return;
+
 	driver_unregister(&hv_driver->driver);
 
 }
@@ -776,6 +791,7 @@ static int __init hv_acpi_init(void)
 
 cleanup:
 	acpi_bus_unregister_driver(&vmbus_acpi_driver);
+	hv_acpi_dev = NULL;
 	return ret;
 }