[PATCH] md: Don't write dirty/clean update to spares - leave them alone

- record the 'event' count on each individual device (they
  might sometimes be slightly different now)
- add a new value for 'sb_dirty': '3' means that the super
  block only needs to be updated to record a clean<->dirty
  transition.
- Prefer odd event numbers for dirty states and even numbers
  for clean states
- Using all the above, don't update the superblock on
  a spare device if the update is just doing a clean-dirty
  transition.  To accomodate this, a transition from
  dirty back to clean might now decrement the events counter
  if nothing else has changed.

The net effect of this is that spare drives will not see any IO requests
during normal running of the array, so they can go to sleep if that is what
they want to do.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 682574f3bd36..c1e0ac55bab5 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -58,6 +58,7 @@ struct mdk_rdev_s
 
         struct page     *sb_page;
         int             sb_loaded;
+        __u64           sb_events;
         sector_t        data_offset;    /* start of data in array */
         sector_t        sb_offset;
         int             sb_size;        /* bytes in the superblock */