md/md-bitmap: introduce struct bitmap_operations

The structure is empty for now, and will be used in later patches to
merge in bitmap operations, so that bitmap implementation won't be
exposed.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240826074452.1490072-12-yukuai1@huaweicloud.comSigned-off-by: Song Liu <song@kernel.org>

drivers/md/md-bitmap.c

@@ -2714,3 +2714,11 @@ const struct attribute_group md_bitmap_group = {
 	.name = "bitmap",
 	.attrs = md_bitmap_attrs,
 };
+
+static struct bitmap_operations bitmap_ops = {
+};
+
+void mddev_set_bitmap_ops(struct mddev *mddev)
+{
+	mddev->bitmap_ops = &bitmap_ops;
+}

drivers/md/md-bitmap.h

@@ -246,7 +246,11 @@ struct md_bitmap_stats {
 	struct file	*file;
 };
 
+struct bitmap_operations {
+};
+
 /* the bitmap API */
+void mddev_set_bitmap_ops(struct mddev *mddev);
 
 /* these are used only by md/bitmap */
 struct bitmap *md_bitmap_create(struct mddev *mddev, int slot);

drivers/md/md.c

@@ -772,6 +772,7 @@ int mddev_init(struct mddev *mddev)
 	mddev->resync_min = 0;
 	mddev->resync_max = MaxSector;
 	mddev->level = LEVEL_NONE;
+	mddev_set_bitmap_ops(mddev);
 
 	INIT_WORK(&mddev->sync_work, md_start_sync);
 	INIT_WORK(&mddev->del_work, mddev_delayed_delete);

drivers/md/md.h

@@ -536,6 +536,7 @@ struct mddev {
 	int				sync_checkers;	/* # of threads checking writes_pending */
 
 	struct bitmap			*bitmap; /* the bitmap for the device */
+	struct bitmap_operations	*bitmap_ops;
 	struct {
 		struct file		*file; /* the bitmap file */
 		loff_t			offset; /* offset from superblock of