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/20250707012711.376844-7-yukuai1@huaweicloud.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>

drivers/md/md-bitmap.c

@@ -232,8 +232,10 @@ static inline char *bmname(struct bitmap *bitmap)
 	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;
 
@@ -245,16 +247,6 @@ static bool __bitmap_enabled(struct bitmap *bitmap, bool flush)
 	       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);
-}
-
 /*
  * check a page and, if necessary, allocate it (or hijack it if the alloc fails)
  *
@@ -1251,7 +1243,7 @@ static void __bitmap_unplug(struct bitmap *bitmap)
 	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

@@ -62,7 +62,7 @@ struct md_bitmap_stats {
 };
 
 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);
 
@@ -107,4 +107,21 @@ struct bitmap_operations {
 /* 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

@@ -140,7 +140,7 @@ static inline bool raid1_add_bio_to_plug(struct mddev *mddev, struct bio *bio,
 	 * 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;
 	}