[PATCH] md: replace magic numbers in sb_dirty with well defined bit flags

Instead of magic numbers (0,1,2,3) in sb_dirty, we have
some flags instead:
MD_CHANGE_DEVS
   Some device state has changed requiring superblock update
   on all devices.
MD_CHANGE_CLEAN
   The array has transitions from 'clean' to 'dirty' or back,
   requiring a superblock update on active devices, but possibly
   not on spares
MD_CHANGE_PENDING
   A superblock update is underway.

We wait for an update to complete by waiting for all flags to be clear.  A
flag can be set at any time, even during an update, without risk that the
change will be lost.

Stop exporting md_update_sb - isn't needed.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4500660..d5a06b2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -696,7 +696,7 @@
 	PRINTK("raid5: error called\n");
 
 	if (!test_bit(Faulty, &rdev->flags)) {
-		mddev->sb_dirty = 1;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
 		if (test_bit(In_sync, &rdev->flags)) {
 			conf->working_disks--;
 			mddev->degraded++;
@@ -2781,9 +2781,9 @@
 		wait_event(conf->wait_for_overlap,
 			   atomic_read(&conf->reshape_stripes)==0);
 		mddev->reshape_position = conf->expand_progress;
-		mddev->sb_dirty = 1;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
 		md_wakeup_thread(mddev->thread);
-		wait_event(mddev->sb_wait, mddev->sb_dirty == 0 ||
+		wait_event(mddev->sb_wait, mddev->flags == 0 ||
 			   kthread_should_stop());
 		spin_lock_irq(&conf->device_lock);
 		conf->expand_lo = mddev->reshape_position;
@@ -3605,7 +3605,7 @@
 	mddev->degraded = (conf->raid_disks - conf->previous_raid_disks) - added_devices;
 	mddev->raid_disks = conf->raid_disks;
 	mddev->reshape_position = 0;
-	mddev->sb_dirty = 1;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);