[PATCH] md: make sure 64bit fields in version-1 metadata are 64-bit aligned

reshape_position is a 64bit field that was not 64bit aligned.  So swap with
new_level.

NOTE: this is a user-visible change.  However:
  - The bad code has not appeared in a released kernel
  - This code is still marked 'experimental'
  - This only affects version-1 superblock, which are not in wide use
  - These field are only used (rather than simply reported) by user-space
    tools in extemely rare circumstances : after a reshape crashes in the
    first second of the reshape process.

So I believe that, at this stage, the change is safe.  Especially if people
heed the 'help' message on use mdadm-2.4.1.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/md/Kconfig

@@ -139,11 +139,12 @@ config MD_RAID5_RESHAPE
 	  is online.  However it is still EXPERIMENTAL code.  It should
 	  work, but please be sure that you have backups.
 
-	  You will need a version of mdadm newer than 2.3.1.   During the
-	  early stage of reshape there is a critical section where live data
-	  is being over-written.  A crash during this time needs extra care
-	  for recovery.  The newer mdadm takes a copy of the data in the
-	  critical section and will restore it, if necessary, after a crash.
+	  You will need mdadm verion 2.4.1 or later to use this
+	  feature safely.  During the early stage of reshape there is
+	  a critical section where live data is being over-written.  A
+	  crash during this time needs extra care for recovery.  The
+	  newer mdadm takes a copy of the data in the critical section
+	  and will restore it, if necessary, after a crash.
 
 	  The mdadm usage is e.g.
 	       mdadm --grow /dev/md1 --raid-disks=6

include/linux/raid/md_p.h

@@ -227,8 +227,8 @@ struct mdp_superblock_1 {
 				 */
 
 	/* These are only valid with feature bit '4' */
-	__u64	reshape_position;	/* next address in array-space for reshape */
 	__u32	new_level;	/* new level we are reshaping to		*/
+	__u64	reshape_position;	/* next address in array-space for reshape */
 	__u32	delta_disks;	/* change in number of raid_disks		*/
 	__u32	new_layout;	/* new layout					*/
 	__u32	new_chunk;	/* new chunk size (bytes)			*/