md/md-bitmap: add md_bitmap_registered/enabled() helper

There are no functional changes, prepare to handle the case that
mddev->bitmap_ops can be NULL, which is possible after introducing
CONFIG_MD_BITMAP.

Link: https://lore.kernel.org/linux-raid/[e-mail]
Signed-off-by: Yu Kuai <[e-mail]>
Reviewed-by: Xiao Ni <[e-mail]>

drivers/md/md-bitmap.c

···
 	return bitmap->mddev ? mdname(bitmap->mddev) : "mdX";
 }
 
-static bool __bitmap_enabled(struct bitmap *bitmap, bool flush)
+static bool bitmap_enabled(void *data, bool flush)
 {
+	struct bitmap *bitmap = data;
+
 	if (!flush)
 		return true;
 
···
 	 */
 	return !test_bit(BITMAP_STALE, &bitmap->flags) &&
 	       bitmap->storage.filemap != NULL;
-}
-
-static bool bitmap_enabled(struct mddev *mddev, bool flush)
-{
-	struct bitmap *bitmap = mddev->bitmap;
-
-	if (!bitmap)
-		return false;
-
-	return __bitmap_enabled(bitmap, flush);
 }
 
 /*
···
 	int dirty, need_write;
 	int writing = 0;
 
-	if (!__bitmap_enabled(bitmap, true))
+	if (!bitmap_enabled(bitmap, true))
 		return;
 
 	/* look at each page to see if there are any set bits that need to be

drivers/md/md-bitmap.h

···
 };
 
 struct bitmap_operations {
-	bool (*enabled)(struct mddev *mddev, bool flush);
+	bool (*enabled)(void *data, bool flush);
 	int (*create)(struct mddev *mddev);
 	int (*resize)(struct mddev *mddev, sector_t blocks, int chunksize);
 
···
 
 /* the bitmap API */
 void mddev_set_bitmap_ops(struct mddev *mddev);
+
+static inline bool md_bitmap_registered(struct mddev *mddev)
+{
+	return mddev->bitmap_ops != NULL;
+}
+
+static inline bool md_bitmap_enabled(struct mddev *mddev, bool flush)
+{
+	/* bitmap_ops must be registered before creating bitmap. */
+	if (!md_bitmap_registered(mddev))
+		return false;
+
+	if (!mddev->bitmap)
+		return false;
+
+	return mddev->bitmap_ops->enabled(mddev->bitmap, flush);
+}
 
 #endif

drivers/md/raid1-10.c

···
 	 * If bitmap is not enabled, it's safe to submit the io directly, and
 	 * this can get optimal performance.
 	 */
-	if (!mddev->bitmap_ops->enabled(mddev, true)) {
+	if (!md_bitmap_enabled(mddev, true)) {
 		raid1_submit_write(bio);
 		return true;
 	}