diff -NurpP linux-2.6.16-rc1-vs2.1.0.9.1/block/ioctl.c linux-2.6.16-rc1-vs2.1.0.9.2/block/ioctl.c
--- linux-2.6.16-rc1-vs2.1.0.9.1/block/ioctl.c	2006-01-18 06:07:58 +0100
+++ linux-2.6.16-rc1-vs2.1.0.9.2/block/ioctl.c	2006-01-29 15:57:21 +0100
@@ -246,6 +246,13 @@ int blkdev_ioctl(struct inode *inode, st
 		set_device_ro(bdev, n);
 		unlock_kernel();
 		return 0;
+
+	case BLKHOLDER:
+		printk("bdev[%p]: holder=%p[%d]\n", bdev, bdev->bd_holder, bdev->bd_holders);
+		if (bdev->bd_holder && bdev->bd_holders)
+			return -EBUSY;
+		return 0;
+
 	case HDIO_GETGEO: {
 		struct hd_geometry geo;
 
diff -NurpP linux-2.6.16-rc1-vs2.1.0.9.1/include/linux/fs.h linux-2.6.16-rc1-vs2.1.0.9.2/include/linux/fs.h
--- linux-2.6.16-rc1-vs2.1.0.9.1/include/linux/fs.h	2006-01-25 05:34:51 +0100
+++ linux-2.6.16-rc1-vs2.1.0.9.2/include/linux/fs.h	2006-01-29 16:01:52 +0100
@@ -207,6 +207,7 @@ extern int dir_notify_enable;
 #define BLKBSZGET  _IOR(0x12,112,size_t)
 #define BLKBSZSET  _IOW(0x12,113,size_t)
 #define BLKGETSIZE64 _IOR(0x12,114,size_t)	/* return device size in bytes (u64 *arg) */
+#define BLKHOLDER  _IO(0x12,115)/* check for bdev holders */
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */