dm: allow offline devices

Allow check_device_area to succeed if a device has an i_size of zero.  This
addresses an issue seen on DASD devices setting up a multipath table for paths
in online and offline state.

Signed-off-by: Mike Anderson <andmike@us.ibm.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/dm-table.c

@@ -425,13 +425,15 @@ static void close_dev(struct dm_dev *d, struct mapped_device *md)
 }
 
 /*
- * If possible (ie. blk_size[major] is set), this checks an area
- * of a destination device is valid.
+ * If possible, this checks an area of a destination device is valid.
  */
 static int check_device_area(struct dm_dev *dd, sector_t start, sector_t len)
 {
-	sector_t dev_size;
-	dev_size = dd->bdev->bd_inode->i_size >> SECTOR_SHIFT;
+	sector_t dev_size = dd->bdev->bd_inode->i_size >> SECTOR_SHIFT;
+
+	if (!dev_size)
+		return 1;
+
 	return ((start < dev_size) && (len <= (dev_size - start)));
 }