md/md-bitmap: add 'events_cleared' into struct md_bitmap_stats

Also add a new helper to get events_cleared to avoid dereferencing
bitmap directly to prepare inventing a new bitmap.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240826074452.1490072-5-yukuai1@huaweicloud.comSigned-off-by: Song Liu <song@kernel.org>

drivers/md/md-bitmap.c

@@ -2104,6 +2104,8 @@ int md_bitmap_get_stats(struct bitmap *bitmap, struct md_bitmap_stats *stats)
 	counts = &bitmap->counts;
 	stats->missing_pages = counts->missing_pages;
 	stats->pages = counts->pages;
+
+	stats->events_cleared = bitmap->events_cleared;
 	stats->file = bitmap->storage.file;
 
 	return 0;

drivers/md/md-bitmap.h

@@ -235,6 +235,7 @@ struct bitmap {
 };
 
 struct md_bitmap_stats {
+	u64		events_cleared;
 	unsigned long	missing_pages;
 	unsigned long	pages;
 	struct file	*file;

drivers/md/md.c

@@ -1372,6 +1372,18 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
 	return ret;
 }
 
+static u64 md_bitmap_events_cleared(struct mddev *mddev)
+{
+	struct md_bitmap_stats stats;
+	int err;
+
+	err = md_bitmap_get_stats(mddev->bitmap, &stats);
+	if (err)
+		return 0;
+
+	return stats.events_cleared;
+}
+
 /*
  * validate_super for 0.90.0
  * note: we are not using "freshest" for 0.9 superblock
@@ -1464,7 +1476,7 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *freshest, stru
 		/* if adding to array with a bitmap, then we can accept an
 		 * older device ... but not too old.
 		 */
-		if (ev1 < mddev->bitmap->events_cleared)
+		if (ev1 < md_bitmap_events_cleared(mddev))
 			return 0;
 		if (ev1 < mddev->events)
 			set_bit(Bitmap_sync, &rdev->flags);
@@ -1991,7 +2003,7 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struc
 		/* If adding to array with a bitmap, then we can accept an
 		 * older device, but not too old.
 		 */
-		if (ev1 < mddev->bitmap->events_cleared)
+		if (ev1 < md_bitmap_events_cleared(mddev))
 			return 0;
 		if (ev1 < mddev->events)
 			set_bit(Bitmap_sync, &rdev->flags);