This is just bd_openers, protected by the bd_mutex.

Signed-off-by: Daniel Stodden <daniel.stodden@xxxxxxxxxx>

diff -r 4d4cc7268176 -r 798c5b306104 drivers/block/xen-blkfront.c
--- a/drivers/block/xen-blkfront.c	Fri Apr 30 14:58:59 2010 -0700
+++ b/drivers/block/xen-blkfront.c	Fri Apr 30 14:58:59 2010 -0700
@@ -94,12 +94,6 @@
 	unsigned long shadow_free;
 	int feature_barrier;
 	int is_ready;
-
-	/**
-	 * The number of people holding this device open.  We won't allow a
-	 * hot-unplug unless this is 0.
-	 */
-	int users;
 };
 
 static DEFINE_SPINLOCK(blkif_io_lock);
@@ -977,7 +971,7 @@
 
 	mutex_lock(&bdev->bd_mutex);
 
-	if (info->users) {
+	if (bdev->bd_openers) {
 		xenbus_dev_error(xbdev, -EBUSY,
 				 "Device in use; refusing to close");
 		xenbus_switch_state(xbdev, XenbusStateClosing);
@@ -1128,7 +1122,7 @@
 	mutex_lock(&bdev->bd_mutex);
 	info = disk->private_data;
 
-	if (info && !info->users) {
+	if (info && !bdev->bd_openers) {
 		xlvbd_release_gendisk(info);
 		disk->private_data = NULL;
 		kfree(info);
@@ -1166,9 +1160,6 @@
 
 	mutex_unlock(&info->mutex);
 
-	if (!err)
-		++info->users;
-
 	return err;
 }
 
@@ -1178,12 +1169,12 @@
 	struct block_device *bdev;
 	struct xenbus_device *xbdev;
 
-	if (--info->users)
-		return 0;
-
 	bdev = bdget_disk(disk, 0);
 	bdput(bdev);
 
+	if (bdev->bd_openers)
+		return 0;
+
 	/*
 	 * Check if we have been instructed to close. We will have
 	 * deferred this request, because the bdev was still open.