md: improve usefulness and accuracy of sysfs file md/sync_completed.

The sync_completed file reports how much of a resync (or recovery or
reshape) has been completed.
However due to the possibility of out-of-order completion of writes,
it is not certain to be accurate.

We have an internal value - mddev->curr_resync_completed - which is an
accurate value (though it might not always be quite so uptodate).

So:
- make curr_resync_completed be uptodate a little more often,
particularly when raid5 reshape updates status in the metadata
- report curr_resync_completed in the sysfs file
- allow poll/select to report all updates to md/sync_completed.

This makes sync_completed completed usable by any external metadata
handler that wants to record this status information in its metadata.

Signed-off-by: NeilBrown <[e-mail]>

drivers/md/bitmap.c

···
 		s += blocks;
 	}
 	bitmap->last_end_sync = jiffies;
+	sysfs_notify(&bitmap->mddev->kobj, NULL, "sync_completed");
 }
 
 static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int needed)

drivers/md/md.c

···
 	clear_bit(MD_CHANGE_PENDING, &mddev->flags);
 	spin_unlock_irq(&mddev->write_lock);
 	wake_up(&mddev->sb_wait);
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
 
 }
 
···
 {
 	unsigned long max_sectors, resync;
 
+	if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+		return sprintf(page, "none\n");
+
 	if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
 		max_sectors = mddev->resync_max_sectors;
 	else
 		max_sectors = mddev->dev_sectors;
 
-	resync = (mddev->curr_resync - atomic_read(&mddev->recovery_active));
+	resync = mddev->curr_resync_completed;
 	return sprintf(page, "%lu / %lu\n", resync, max_sectors);
 }
 
···
 		sector_t sectors;
 
 		skipped = 0;
-		if (j >= mddev->resync_max) {
-			sysfs_notify(&mddev->kobj, NULL, "sync_completed");
-			wait_event(mddev->recovery_wait,
-				   mddev->resync_max > j
-				   || kthread_should_stop());
-		}
-		if (kthread_should_stop())
-			goto interrupted;
 
-		if (mddev->curr_resync > mddev->curr_resync_completed &&
-		    (mddev->curr_resync - mddev->curr_resync_completed)
-		    > (max_sectors >> 4)) {
+		if ((mddev->curr_resync > mddev->curr_resync_completed &&
+		     (mddev->curr_resync - mddev->curr_resync_completed)
+		    > (max_sectors >> 4)) ||
+		    j >= mddev->resync_max
+			) {
 			/* time to update curr_resync_completed */
 			blk_unplug(mddev->queue);
 			wait_event(mddev->recovery_wait,
···
 			mddev->curr_resync_completed =
 				mddev->curr_resync;
 			set_bit(MD_CHANGE_CLEAN, &mddev->flags);
+			sysfs_notify(&mddev->kobj, NULL, "sync_completed");
 		}
+
+		if (j >= mddev->resync_max)
+			wait_event(mddev->recovery_wait,
+				   mddev->resync_max > j
+				   || kthread_should_stop());
+
+		if (kthread_should_stop())
+			goto interrupted;
+
 		sectors = mddev->pers->sync_request(mddev, j, &skipped,
 						  currspeed < speed_min(mddev));
 		if (sectors == 0) {
···
 
  skip:
 	mddev->curr_resync = 0;
+	mddev->curr_resync_completed = 0;
 	mddev->resync_min = 0;
 	mddev->resync_max = MaxSector;
 	sysfs_notify(&mddev->kobj, NULL, "sync_completed");

drivers/md/raid5.c

···
 		wait_event(conf->wait_for_overlap,
 			   atomic_read(&conf->reshape_stripes)==0);
 		mddev->reshape_position = conf->reshape_progress;
+		mddev->curr_resync_completed = mddev->curr_resync;
 		conf->reshape_checkpoint = jiffies;
 		set_bit(MD_CHANGE_DEVS, &mddev->flags);
 		md_wakeup_thread(mddev->thread);
···
 		conf->reshape_safe = mddev->reshape_position;
 		spin_unlock_irq(&conf->device_lock);
 		wake_up(&conf->wait_for_overlap);
+		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
 	}
 
 	if (mddev->delta_disks < 0) {
···
 		wait_event(conf->wait_for_overlap,
 			   atomic_read(&conf->reshape_stripes) == 0);
 		mddev->reshape_position = conf->reshape_progress;
+		mddev->curr_resync_completed = mddev->curr_resync;
 		conf->reshape_checkpoint = jiffies;
 		set_bit(MD_CHANGE_DEVS, &mddev->flags);
 		md_wakeup_thread(mddev->thread);
···
 		conf->reshape_safe = mddev->reshape_position;
 		spin_unlock_irq(&conf->device_lock);
 		wake_up(&conf->wait_for_overlap);
+		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
 	}
 	return reshape_sectors;
 }