v4.19.13 snapshot.
diff --git a/fs/btrfs/async-thread.h b/fs/btrfs/async-thread.h
new file mode 100644
index 0000000..7861c9f
--- /dev/null
+++ b/fs/btrfs/async-thread.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2007 Oracle. All rights reserved.
+ * Copyright (C) 2014 Fujitsu. All rights reserved.
+ */
+
+#ifndef BTRFS_ASYNC_THREAD_H
+#define BTRFS_ASYNC_THREAD_H
+
+#include <linux/workqueue.h>
+
+struct btrfs_fs_info;
+struct btrfs_workqueue;
+/* Internal use only */
+struct __btrfs_workqueue;
+struct btrfs_work;
+typedef void (*btrfs_func_t)(struct btrfs_work *arg);
+typedef void (*btrfs_work_func_t)(struct work_struct *arg);
+
+struct btrfs_work {
+ btrfs_func_t func;
+ btrfs_func_t ordered_func;
+ btrfs_func_t ordered_free;
+
+ /* Don't touch things below */
+ struct work_struct normal_work;
+ struct list_head ordered_list;
+ struct __btrfs_workqueue *wq;
+ unsigned long flags;
+};
+
+#define BTRFS_WORK_HELPER_PROTO(name) \
+void btrfs_##name(struct work_struct *arg)
+
+BTRFS_WORK_HELPER_PROTO(worker_helper);
+BTRFS_WORK_HELPER_PROTO(delalloc_helper);
+BTRFS_WORK_HELPER_PROTO(flush_delalloc_helper);
+BTRFS_WORK_HELPER_PROTO(cache_helper);
+BTRFS_WORK_HELPER_PROTO(submit_helper);
+BTRFS_WORK_HELPER_PROTO(fixup_helper);
+BTRFS_WORK_HELPER_PROTO(endio_helper);
+BTRFS_WORK_HELPER_PROTO(endio_meta_helper);
+BTRFS_WORK_HELPER_PROTO(endio_meta_write_helper);
+BTRFS_WORK_HELPER_PROTO(endio_raid56_helper);
+BTRFS_WORK_HELPER_PROTO(endio_repair_helper);
+BTRFS_WORK_HELPER_PROTO(rmw_helper);
+BTRFS_WORK_HELPER_PROTO(endio_write_helper);
+BTRFS_WORK_HELPER_PROTO(freespace_write_helper);
+BTRFS_WORK_HELPER_PROTO(delayed_meta_helper);
+BTRFS_WORK_HELPER_PROTO(readahead_helper);
+BTRFS_WORK_HELPER_PROTO(qgroup_rescan_helper);
+BTRFS_WORK_HELPER_PROTO(extent_refs_helper);
+BTRFS_WORK_HELPER_PROTO(scrub_helper);
+BTRFS_WORK_HELPER_PROTO(scrubwrc_helper);
+BTRFS_WORK_HELPER_PROTO(scrubnc_helper);
+BTRFS_WORK_HELPER_PROTO(scrubparity_helper);
+
+
+struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info,
+ const char *name,
+ unsigned int flags,
+ int limit_active,
+ int thresh);
+void btrfs_init_work(struct btrfs_work *work, btrfs_work_func_t helper,
+ btrfs_func_t func,
+ btrfs_func_t ordered_func,
+ btrfs_func_t ordered_free);
+void btrfs_queue_work(struct btrfs_workqueue *wq,
+ struct btrfs_work *work);
+void btrfs_destroy_workqueue(struct btrfs_workqueue *wq);
+void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int max);
+void btrfs_set_work_high_priority(struct btrfs_work *work);
+struct btrfs_fs_info *btrfs_work_owner(const struct btrfs_work *work);
+struct btrfs_fs_info *btrfs_workqueue_owner(const struct __btrfs_workqueue *wq);
+bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq);
+
+#endif