md/md-bitmap: introduce CONFIG_MD_BITMAP

Now that all implementations are internal, it's sensible to add a config
option for md-bitmap, and it's a good way for isolation.

Link: https://lore.kernel.org/linux-raid/20250707012711.376844-16-yukuai1@huaweicloud.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>

drivers/md/Kconfig

@@ -37,6 +37,21 @@ config BLK_DEV_MD
 
 	  If unsure, say N.
 
+config MD_BITMAP
+	bool "MD RAID bitmap support"
+	default y
+	depends on BLK_DEV_MD
+	help
+	  If you say Y here, support for the write intent bitmap will be
+	  enabled. The bitmap can be used to optimize resync speed after power
+	  failure or readding a disk, limiting it to recorded dirty sectors in
+	  bitmap.
+
+	  This feature can be added to existing MD array or MD array can be
+	  created with bitmap via mdadm(8).
+
+	  If unsure, say Y.
+
 config MD_AUTODETECT
 	bool "Autodetect RAID arrays during kernel boot"
 	depends on BLK_DEV_MD=y
@@ -54,6 +69,7 @@ config MD_AUTODETECT
 config MD_BITMAP_FILE
 	bool "MD bitmap file support (deprecated)"
 	default y
+	depends on MD_BITMAP
 	help
 	  If you say Y here, support for write intent bitmaps in files on an
 	  external file system is enabled.  This is an alternative to the internal
@@ -174,6 +190,7 @@ config MD_RAID456
 
 config MD_CLUSTER
 	tristate "Cluster Support for MD"
+	select MD_BITMAP
 	depends on BLK_DEV_MD
 	depends on DLM
 	default n
@@ -393,6 +410,7 @@ config DM_RAID
        select MD_RAID1
        select MD_RAID10
        select MD_RAID456
+       select MD_BITMAP
        select BLK_DEV_MD
 	help
 	 A dm target that supports RAID1, RAID10, RAID4, RAID5 and RAID6 mappings

drivers/md/Makefile

@@ -27,7 +27,8 @@ dm-clone-y	+= dm-clone-target.o dm-clone-metadata.o
 dm-verity-y	+= dm-verity-target.o
 dm-zoned-y	+= dm-zoned-target.o dm-zoned-metadata.o dm-zoned-reclaim.o
 
-md-mod-y	+= md.o md-bitmap.o
+md-mod-y	+= md.o
+md-mod-$(CONFIG_MD_BITMAP)	+= md-bitmap.o
 raid456-y	+= raid5.o raid5-cache.o raid5-ppl.o
 linear-y       += md-linear.o
 

drivers/md/md-bitmap.c

@@ -224,6 +224,8 @@ struct bitmap {
 	int cluster_slot;
 };
 
+static struct workqueue_struct *md_bitmap_wq;
+
 static int __bitmap_resize(struct bitmap *bitmap, sector_t blocks,
 			   int chunksize, bool init);
 
@@ -2979,6 +2981,12 @@ static struct attribute_group md_bitmap_group = {
 };
 
 static struct bitmap_operations bitmap_ops = {
+	.head = {
+		.type	= MD_BITMAP,
+		.id	= ID_BITMAP,
+		.name	= "bitmap",
+	},
+
 	.enabled		= bitmap_enabled,
 	.create			= bitmap_create,
 	.resize			= bitmap_resize,
@@ -3013,7 +3021,18 @@ static struct bitmap_operations bitmap_ops = {
 	.group			= &md_bitmap_group,
 };
 
-void mddev_set_bitmap_ops(struct mddev *mddev)
+int md_bitmap_init(void)
 {
-	mddev->bitmap_ops = &bitmap_ops;
+	md_bitmap_wq = alloc_workqueue("md_bitmap", WQ_MEM_RECLAIM | WQ_UNBOUND,
+				       0);
+	if (!md_bitmap_wq)
+		return -ENOMEM;
+
+	return register_md_submodule(&bitmap_ops.head);
+}
+
+void md_bitmap_exit(void)
+{
+	destroy_workqueue(md_bitmap_wq);
+	unregister_md_submodule(&bitmap_ops.head);
 }

drivers/md/md-bitmap.h

@@ -62,6 +62,8 @@ struct md_bitmap_stats {
 };
 
 struct bitmap_operations {
+	struct md_submodule_head head;
+
 	bool (*enabled)(void *data, bool flush);
 	int (*create)(struct mddev *mddev);
 	int (*resize)(struct mddev *mddev, sector_t blocks, int chunksize);
@@ -105,8 +107,6 @@ 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;
@@ -147,4 +147,17 @@ static inline void md_bitmap_end_sync(struct mddev *mddev, sector_t offset,
 	mddev->bitmap_ops->end_sync(mddev, offset, blocks);
 }
 
+#ifdef CONFIG_MD_BITMAP
+int md_bitmap_init(void);
+void md_bitmap_exit(void);
+#else
+static inline int md_bitmap_init(void)
+{
+	return 0;
+}
+static inline void md_bitmap_exit(void)
+{
+}
+#endif
+
 #endif

drivers/md/md.c

@@ -94,7 +94,6 @@ static struct workqueue_struct *md_wq;
  * workqueue whith reconfig_mutex grabbed.
  */
 static struct workqueue_struct *md_misc_wq;
-struct workqueue_struct *md_bitmap_wq;
 
 static int remove_and_add_spares(struct mddev *mddev,
 				 struct md_rdev *this);
@@ -677,15 +676,34 @@ static void active_io_release(struct percpu_ref *ref)
 
 static void no_op(struct percpu_ref *r) {}
 
+static void mddev_set_bitmap_ops(struct mddev *mddev, enum md_submodule_id id)
+{
+	xa_lock(&md_submodule);
+	mddev->bitmap_ops = xa_load(&md_submodule, id);
+	xa_unlock(&md_submodule);
+	if (!mddev->bitmap_ops)
+		pr_warn_once("md: can't find bitmap id %d\n", id);
+}
+
+static void mddev_clear_bitmap_ops(struct mddev *mddev)
+{
+	mddev->bitmap_ops = NULL;
+}
+
 int mddev_init(struct mddev *mddev)
 {
+	/* TODO: support more versions */
+	mddev_set_bitmap_ops(mddev, ID_BITMAP);
 
 	if (percpu_ref_init(&mddev->active_io, active_io_release,
-			    PERCPU_REF_ALLOW_REINIT, GFP_KERNEL))
+			    PERCPU_REF_ALLOW_REINIT, GFP_KERNEL)) {
+		mddev_clear_bitmap_ops(mddev);
 		return -ENOMEM;
+	}
 
 	if (percpu_ref_init(&mddev->writes_pending, no_op,
 			    PERCPU_REF_ALLOW_REINIT, GFP_KERNEL)) {
+		mddev_clear_bitmap_ops(mddev);
 		percpu_ref_exit(&mddev->active_io);
 		return -ENOMEM;
 	}
@@ -713,7 +731,6 @@ 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);
@@ -724,6 +741,7 @@ EXPORT_SYMBOL_GPL(mddev_init);
 
 void mddev_destroy(struct mddev *mddev)
 {
+	mddev_clear_bitmap_ops(mddev);
 	percpu_ref_exit(&mddev->active_io);
 	percpu_ref_exit(&mddev->writes_pending);
 }
@@ -10121,8 +10139,12 @@ static void md_geninit(void)
 
 static int __init md_init(void)
 {
-	int ret = -ENOMEM;
+	int ret = md_bitmap_init();
 
+	if (ret)
+		return ret;
+
+	ret = -ENOMEM;
 	md_wq = alloc_workqueue("md", WQ_MEM_RECLAIM, 0);
 	if (!md_wq)
 		goto err_wq;
@@ -10131,11 +10153,6 @@ static int __init md_init(void)
 	if (!md_misc_wq)
 		goto err_misc_wq;
 
-	md_bitmap_wq = alloc_workqueue("md_bitmap", WQ_MEM_RECLAIM | WQ_UNBOUND,
-				       0);
-	if (!md_bitmap_wq)
-		goto err_bitmap_wq;
-
 	ret = __register_blkdev(MD_MAJOR, "md", md_probe);
 	if (ret < 0)
 		goto err_md;
@@ -10154,12 +10171,11 @@ static int __init md_init(void)
 err_mdp:
 	unregister_blkdev(MD_MAJOR, "md");
 err_md:
-	destroy_workqueue(md_bitmap_wq);
-err_bitmap_wq:
 	destroy_workqueue(md_misc_wq);
 err_misc_wq:
 	destroy_workqueue(md_wq);
 err_wq:
+	md_bitmap_exit();
 	return ret;
 }
 
@@ -10465,8 +10481,8 @@ static __exit void md_exit(void)
 	spin_unlock(&all_mddevs_lock);
 
 	destroy_workqueue(md_misc_wq);
-	destroy_workqueue(md_bitmap_wq);
 	destroy_workqueue(md_wq);
+	md_bitmap_exit();
 }
 
 subsys_initcall(md_init);

drivers/md/md.h

@@ -38,7 +38,7 @@ enum md_submodule_id {
 	ID_RAID6	= 6,
 	ID_RAID10	= 10,
 	ID_CLUSTER,
-	ID_BITMAP,	/* TODO */
+	ID_BITMAP,
 	ID_LLBITMAP,	/* TODO */
 };
 
@@ -1012,7 +1012,6 @@ struct mdu_array_info_s;
 struct mdu_disk_info_s;
 
 extern int mdp_major;
-extern struct workqueue_struct *md_bitmap_wq;
 void md_autostart_arrays(int part);
 int md_set_array_info(struct mddev *mddev, struct mdu_array_info_s *info);
 int md_add_new_disk(struct mddev *mddev, struct mdu_disk_info_s *info);