md/md-bitmap: add a none backend for bitmap grow

Add a real none bitmap backend that exposes the common bitmap sysfs
group and use it to keep bitmap/location available when an array has no
bitmap.

Then switch the bitmap location sysfs path to move only between none
and the classic bitmap backend, using the no-sysfs bitmap helpers while
merging or unmerging the internal bitmap sysfs group.

This restores mdadm --grow bitmap addition through bitmap/location.

Fixes: fb8cc3b0d9 ("md/md-bitmap: delay registration of bitmap_ops until creating bitmap")
Reviewed-by: Su Yue <glass.su@suse.com>
Link: https://lore.kernel.org/r/20260425024615.1696892-4-yukuai@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>

drivers/md/md-bitmap.c

@@ -216,6 +216,7 @@ struct bitmap {
 };
 
 static struct workqueue_struct *md_bitmap_wq;
+static struct attribute_group md_bitmap_internal_group;
 
 static int __bitmap_resize(struct bitmap *bitmap, sector_t blocks,
 			   int chunksize, bool init);
@@ -2580,6 +2581,30 @@ static int bitmap_resize(struct mddev *mddev, sector_t blocks, int chunksize)
 	return __bitmap_resize(bitmap, blocks, chunksize, false);
 }
 
+static bool bitmap_none_enabled(void *data, bool flush)
+{
+	return false;
+}
+
+static int bitmap_none_create(struct mddev *mddev)
+{
+	return 0;
+}
+
+static int bitmap_none_load(struct mddev *mddev)
+{
+	return 0;
+}
+
+static void bitmap_none_destroy(struct mddev *mddev)
+{
+}
+
+static int bitmap_none_get_stats(void *data, struct md_bitmap_stats *stats)
+{
+	return -ENOENT;
+}
+
 static ssize_t
 location_show(struct mddev *mddev, char *page)
 {
@@ -2618,7 +2643,11 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 			goto out;
 		}
 
-		bitmap_destroy(mddev);
+		sysfs_unmerge_group(&mddev->kobj, &md_bitmap_internal_group);
+		md_bitmap_destroy_nosysfs(mddev);
+		mddev->bitmap_id = ID_BITMAP_NONE;
+		if (!mddev_set_bitmap_ops_nosysfs(mddev))
+			goto none_err;
 		mddev->bitmap_info.offset = 0;
 		if (mddev->bitmap_info.file) {
 			struct file *f = mddev->bitmap_info.file;
@@ -2654,16 +2683,25 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 			}
 
 			mddev->bitmap_info.offset = offset;
-			rv = bitmap_create(mddev);
-			if (rv)
-				goto out;
+			md_bitmap_destroy_nosysfs(mddev);
+			mddev->bitmap_id = ID_BITMAP;
+			if (!mddev_set_bitmap_ops_nosysfs(mddev))
+				goto bitmap_err;
 
-			rv = bitmap_load(mddev);
+			rv = md_bitmap_create_nosysfs(mddev);
+			if (rv)
+				goto create_err;
+
+			rv = mddev->bitmap_ops->load(mddev);
 			if (rv) {
 				mddev->bitmap_info.offset = 0;
-				bitmap_destroy(mddev);
-				goto out;
+				goto load_err;
 			}
+
+			rv = sysfs_merge_group(&mddev->kobj,
+					       &md_bitmap_internal_group);
+			if (rv)
+				goto merge_err;
 		}
 	}
 	if (!mddev->external) {
@@ -2679,6 +2717,22 @@ location_store(struct mddev *mddev, const char *buf, size_t len)
 	if (rv)
 		return rv;
 	return len;
+
+merge_err:
+	mddev->bitmap_info.offset = 0;
+load_err:
+	md_bitmap_destroy_nosysfs(mddev);
+create_err:
+	mddev->bitmap_info.offset = 0;
+	mddev->bitmap_id = ID_BITMAP_NONE;
+	if (!mddev_set_bitmap_ops_nosysfs(mddev))
+		rv = -ENOENT;
+	goto out;
+bitmap_err:
+	rv = -ENOENT;
+none_err:
+	mddev->bitmap_info.offset = 0;
+	goto out;
 }
 
 static struct md_sysfs_entry bitmap_location =
@@ -2987,6 +3041,27 @@ static const struct attribute_group *bitmap_groups[] = {
 	NULL,
 };
 
+static const struct attribute_group *bitmap_none_groups[] = {
+	&md_bitmap_common_group,
+	NULL,
+};
+
+static struct bitmap_operations bitmap_none_ops = {
+	.head = {
+		.type	= MD_BITMAP,
+		.id	= ID_BITMAP_NONE,
+		.name	= "none",
+	},
+
+	.enabled		= bitmap_none_enabled,
+	.create			= bitmap_none_create,
+	.load			= bitmap_none_load,
+	.destroy		= bitmap_none_destroy,
+	.get_stats		= bitmap_none_get_stats,
+
+	.groups			= bitmap_none_groups,
+};
+
 static struct bitmap_operations bitmap_ops = {
 	.head = {
 		.type	= MD_BITMAP,
@@ -3033,16 +3108,33 @@ static struct bitmap_operations bitmap_ops = {
 
 int md_bitmap_init(void)
 {
+	int err;
+
 	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);
+	err = register_md_submodule(&bitmap_none_ops.head);
+	if (err)
+		goto err_wq;
+
+	err = register_md_submodule(&bitmap_ops.head);
+	if (err)
+		goto err_none;
+
+	return 0;
+
+err_none:
+	unregister_md_submodule(&bitmap_none_ops.head);
+err_wq:
+	destroy_workqueue(md_bitmap_wq);
+	return err;
 }
 
 void md_bitmap_exit(void)
 {
-	destroy_workqueue(md_bitmap_wq);
 	unregister_md_submodule(&bitmap_ops.head);
+	unregister_md_submodule(&bitmap_none_ops.head);
+	destroy_workqueue(md_bitmap_wq);
 }

drivers/md/md.c

@@ -705,7 +705,7 @@ static void md_bitmap_sysfs_del(struct mddev *mddev)
 	sysfs_remove_group(&mddev->kobj, mddev->bitmap_ops->groups[0]);
 }
 
-static bool mddev_set_bitmap_ops_nosysfs(struct mddev *mddev)
+bool mddev_set_bitmap_ops_nosysfs(struct mddev *mddev)
 {
 	struct md_submodule_head *head;
 
@@ -4275,7 +4275,7 @@ bitmap_type_show(struct mddev *mddev, char *page)
 
 	xa_lock(&md_submodule);
 	xa_for_each(&md_submodule, i, head) {
-		if (head->type != MD_BITMAP)
+		if (head->type != MD_BITMAP || head->id == ID_BITMAP_NONE)
 			continue;
 
 		if (mddev->bitmap_id == head->id)
@@ -6535,7 +6535,7 @@ static enum md_submodule_id md_bitmap_get_id_from_sb(struct mddev *mddev)
 	return id;
 }
 
-static int md_bitmap_create_nosysfs(struct mddev *mddev)
+int md_bitmap_create_nosysfs(struct mddev *mddev)
 {
 	enum md_submodule_id orig_id = mddev->bitmap_id;
 	enum md_submodule_id sb_id;
@@ -6544,8 +6544,10 @@ static int md_bitmap_create_nosysfs(struct mddev *mddev)
 	if (mddev->bitmap_id == ID_BITMAP_NONE)
 		return -EINVAL;
 
-	if (!mddev_set_bitmap_ops_nosysfs(mddev))
+	if (!mddev_set_bitmap_ops_nosysfs(mddev)) {
+		mddev->bitmap_id = orig_id;
 		return -ENOENT;
+	}
 
 	err = mddev->bitmap_ops->create(mddev);
 	if (!err)
@@ -6559,8 +6561,10 @@ static int md_bitmap_create_nosysfs(struct mddev *mddev)
 	mddev->bitmap_ops = NULL;
 
 	sb_id = md_bitmap_get_id_from_sb(mddev);
-	if (sb_id == ID_BITMAP_NONE || sb_id == orig_id)
+	if (sb_id == ID_BITMAP_NONE || sb_id == orig_id) {
+		mddev->bitmap_id = orig_id;
 		return err;
+	}
 
 	pr_info("md: %s: bitmap version mismatch, switching from %d to %d\n",
 		mdname(mddev), orig_id, sb_id);
@@ -6594,7 +6598,7 @@ static int md_bitmap_create(struct mddev *mddev)
 	return 0;
 }
 
-static void md_bitmap_destroy_nosysfs(struct mddev *mddev)
+void md_bitmap_destroy_nosysfs(struct mddev *mddev)
 {
 	if (!md_bitmap_registered(mddev))
 		return;
@@ -6612,6 +6616,16 @@ static void md_bitmap_destroy(struct mddev *mddev)
 	md_bitmap_destroy_nosysfs(mddev);
 }
 
+static void md_bitmap_set_none(struct mddev *mddev)
+{
+	mddev->bitmap_id = ID_BITMAP_NONE;
+	if (!mddev_set_bitmap_ops_nosysfs(mddev))
+		return;
+
+	if (!mddev_is_dm(mddev) && mddev->bitmap_ops->groups)
+		md_bitmap_sysfs_add(mddev);
+}
+
 int md_run(struct mddev *mddev)
 {
 	int err;
@@ -6821,6 +6835,10 @@ int md_run(struct mddev *mddev)
 	if (mddev->sb_flags)
 		md_update_sb(mddev, 0);
 
+	if (IS_ENABLED(CONFIG_MD_BITMAP) && !mddev->bitmap_info.file &&
+	    !mddev->bitmap_info.offset)
+		md_bitmap_set_none(mddev);
+
 	md_new_event();
 	return 0;
 
@@ -7766,7 +7784,8 @@ static int set_bitmap_file(struct mddev *mddev, int fd)
 {
 	int err = 0;
 
-	if (!md_bitmap_registered(mddev))
+	if (!md_bitmap_registered(mddev) ||
+	    mddev->bitmap_id == ID_BITMAP_NONE)
 		return -EINVAL;
 
 	if (mddev->pers) {
@@ -7831,10 +7850,12 @@ static int set_bitmap_file(struct mddev *mddev, int fd)
 
 			if (err) {
 				md_bitmap_destroy(mddev);
+				md_bitmap_set_none(mddev);
 				fd = -1;
 			}
 		} else if (fd < 0) {
 			md_bitmap_destroy(mddev);
+			md_bitmap_set_none(mddev);
 		}
 	}
 
@@ -8141,12 +8162,16 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 				mddev->bitmap_info.default_offset;
 			mddev->bitmap_info.space =
 				mddev->bitmap_info.default_space;
+			mddev->bitmap_id = ID_BITMAP;
 			rv = md_bitmap_create(mddev);
 			if (!rv)
 				rv = mddev->bitmap_ops->load(mddev);
 
-			if (rv)
+			if (rv) {
 				md_bitmap_destroy(mddev);
+				mddev->bitmap_info.offset = 0;
+				md_bitmap_set_none(mddev);
+			}
 		} else {
 			struct md_bitmap_stats stats;
 
@@ -8174,6 +8199,7 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 			}
 			md_bitmap_destroy(mddev);
 			mddev->bitmap_info.offset = 0;
+			md_bitmap_set_none(mddev);
 		}
 	}
 	md_update_sb(mddev, 1);

drivers/md/md.h

@@ -934,6 +934,9 @@ extern void md_allow_write(struct mddev *mddev);
 extern void md_wait_for_blocked_rdev(struct md_rdev *rdev, struct mddev *mddev);
 extern void md_set_array_sectors(struct mddev *mddev, sector_t array_sectors);
 extern int md_check_no_bitmap(struct mddev *mddev);
+bool mddev_set_bitmap_ops_nosysfs(struct mddev *mddev);
+int md_bitmap_create_nosysfs(struct mddev *mddev);
+void md_bitmap_destroy_nosysfs(struct mddev *mddev);
 extern int md_integrity_register(struct mddev *mddev);
 extern int strict_strtoul_scaled(const char *cp, unsigned long *res, int scale);