md: introduce link/unlink_rdev() helpers

There are places where sysfs links to rdev are handled
in a same way. Add the helper functions to consolidate
them.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 1c26c7a..6863f72 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -413,6 +413,20 @@
 	return mddev->gendisk ? mddev->gendisk->disk_name : "mdX";
 }
 
+static inline int sysfs_link_rdev(mddev_t *mddev, mdk_rdev_t *rdev)
+{
+	char nm[20];
+	sprintf(nm, "rd%d", rdev->raid_disk);
+	return sysfs_create_link(&mddev->kobj, &rdev->kobj, nm);
+}
+
+static inline void sysfs_unlink_rdev(mddev_t *mddev, mdk_rdev_t *rdev)
+{
+	char nm[20];
+	sprintf(nm, "rd%d", rdev->raid_disk);
+	sysfs_remove_link(&mddev->kobj, nm);
+}
+
 /*
  * iterates through some rdev ringlist. It's safe to remove the
  * current 'rdev'. Dont touch 'tmp' though.