diff -Naurp a/drivers/md/dm.c b/drivers/md/dm.c
--- a/drivers/md/dm.c	2006-01-14 22:16:02.000000000 -0800
+++ b/drivers/md/dm.c	2006-02-09 14:05:18.000000000 -0800
@@ -17,6 +17,7 @@
 #include <linux/mempool.h>
 #include <linux/slab.h>
 #include <linux/idr.h>
+#include <linux/hdreg.h>
 
 static const char *_name = DM_NAME;
 
@@ -223,6 +224,47 @@ static int dm_blk_close(struct inode *in
 	return 0;
 }
 
+static int dm_blk_ioctl(struct inode * inode, struct file * filp,
+			unsigned int cmd, unsigned long arg)
+{
+	struct block_device *bdev = inode->i_bdev;
+	struct hd_geometry __user *loc = (void __user *)arg;
+	struct mapped_device *md;
+	int diskinfo[4];
+
+	if (cmd == HDIO_GETGEO) {
+		if (!arg)
+			return -EINVAL;
+
+		/* Make up some fake geometry. */
+		md = bdev->bd_disk->private_data;
+		diskinfo[0] = 0x40;	/* 1 << 6 */
+		diskinfo[1] = 0x20;	/* 1 << 5 */
+		diskinfo[2] = md->disk->capacity >> 11;
+		diskinfo[3] = 0;
+
+		/* cylinder count too big? */
+		if (diskinfo[2] > 65536) {
+			diskinfo[0] = 255;
+			diskinfo[1] = 63;
+			diskinfo[2] = md->disk->capacity / 16065; /* 255*63 */
+		}
+
+		if (put_user(diskinfo[0], &loc->heads))
+			return -EFAULT;
+		if (put_user(diskinfo[1], &loc->sectors))
+			return -EFAULT;
+		if (put_user(diskinfo[2], &loc->cylinders))
+			return -EFAULT;
+		if (put_user(diskinfo[3], &loc->start))
+			return -EFAULT;
+
+		return 0;
+	}
+
+	return -ENOTTY;
+}
+
 static inline struct dm_io *alloc_io(struct mapped_device *md)
 {
 	return mempool_alloc(md->io_pool, GFP_NOIO);
@@ -1179,6 +1221,7 @@ int dm_suspended(struct mapped_device *m
 static struct block_device_operations dm_blk_dops = {
 	.open = dm_blk_open,
 	.release = dm_blk_close,
+	.ioctl = dm_blk_ioctl,
 	.owner = THIS_MODULE
 };