diff --git a/fs/nilfs2/btnode.c b/fs/nilfs2/btnode.c
new file mode 100644
index 0000000..ebb24a3
--- /dev/null
+++ b/fs/nilfs2/btnode.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * btnode.c - NILFS B-tree node cache
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * Originally written by Seiji Kihara.
+ * Fully revised by Ryusuke Konishi for stabilization and simplification.
+ *
+ */
+
+#include <linux/types.h>
+#include <linux/buffer_head.h>
+#include <linux/mm.h>
+#include <linux/backing-dev.h>
+#include <linux/gfp.h>
+#include "nilfs.h"
+#include "mdt.h"
+#include "dat.h"
+#include "page.h"
+#include "btnode.h"
+
+void nilfs_btnode_cache_clear(struct address_space *btnc)
+{
+	invalidate_mapping_pages(btnc, 0, -1);
+	truncate_inode_pages(btnc, 0);
+}
+
+struct buffer_head *
+nilfs_btnode_create_block(struct address_space *btnc, __u64 blocknr)
+{
+	struct inode *inode = NILFS_BTNC_I(btnc);
+	struct buffer_head *bh;
+
+	bh = nilfs_grab_buffer(inode, btnc, blocknr, BIT(BH_NILFS_Node));
+	if (unlikely(!bh))
+		return NULL;
+
+	if (unlikely(buffer_mapped(bh) || buffer_uptodate(bh) ||
+		     buffer_dirty(bh))) {
+		brelse(bh);
+		BUG();
+	}
+	memset(bh->b_data, 0, i_blocksize(inode));
+	bh->b_bdev = inode->i_sb->s_bdev;
+	bh->b_blocknr = blocknr;
+	set_buffer_mapped(bh);
+	set_buffer_uptodate(bh);
+
+	unlock_page(bh->b_page);
+	put_page(bh->b_page);
+	return bh;
+}
+
+int nilfs_btnode_submit_block(struct address_space *btnc, __u64 blocknr,
+			      sector_t pblocknr, int mode, int mode_flags,
+			      struct buffer_head **pbh, sector_t *submit_ptr)
+{
+	struct buffer_head *bh;
+	struct inode *inode = NILFS_BTNC_I(btnc);
+	struct page *page;
+	int err;
+
+	bh = nilfs_grab_buffer(inode, btnc, blocknr, BIT(BH_NILFS_Node));
+	if (unlikely(!bh))
+		return -ENOMEM;
+
+	err = -EEXIST; /* internal code */
+	page = bh->b_page;
+
+	if (buffer_uptodate(bh) || buffer_dirty(bh))
+		goto found;
+
+	if (pblocknr == 0) {
+		pblocknr = blocknr;
+		if (inode->i_ino != NILFS_DAT_INO) {
+			struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
+
+			/* blocknr is a virtual block number */
+			err = nilfs_dat_translate(nilfs->ns_dat, blocknr,
+						  &pblocknr);
+			if (unlikely(err)) {
+				brelse(bh);
+				goto out_locked;
+			}
+		}
+	}
+
+	if (mode_flags & REQ_RAHEAD) {
+		if (pblocknr != *submit_ptr + 1 || !trylock_buffer(bh)) {
+			err = -EBUSY; /* internal code */
+			brelse(bh);
+			goto out_locked;
+		}
+	} else { /* mode == READ */
+		lock_buffer(bh);
+	}
+	if (buffer_uptodate(bh)) {
+		unlock_buffer(bh);
+		err = -EEXIST; /* internal code */
+		goto found;
+	}
+	set_buffer_mapped(bh);
+	bh->b_bdev = inode->i_sb->s_bdev;
+	bh->b_blocknr = pblocknr; /* set block address for read */
+	bh->b_end_io = end_buffer_read_sync;
+	get_bh(bh);
+	submit_bh(mode, mode_flags, bh);
+	bh->b_blocknr = blocknr; /* set back to the given block address */
+	*submit_ptr = pblocknr;
+	err = 0;
+found:
+	*pbh = bh;
+
+out_locked:
+	unlock_page(page);
+	put_page(page);
+	return err;
+}
+
+/**
+ * nilfs_btnode_delete - delete B-tree node buffer
+ * @bh: buffer to be deleted
+ *
+ * nilfs_btnode_delete() invalidates the specified buffer and delete the page
+ * including the buffer if the page gets unbusy.
+ */
+void nilfs_btnode_delete(struct buffer_head *bh)
+{
+	struct address_space *mapping;
+	struct page *page = bh->b_page;
+	pgoff_t index = page_index(page);
+	int still_dirty;
+
+	get_page(page);
+	lock_page(page);
+	wait_on_page_writeback(page);
+
+	nilfs_forget_buffer(bh);
+	still_dirty = PageDirty(page);
+	mapping = page->mapping;
+	unlock_page(page);
+	put_page(page);
+
+	if (!still_dirty && mapping)
+		invalidate_inode_pages2_range(mapping, index, index);
+}
+
+/**
+ * nilfs_btnode_prepare_change_key
+ *  prepare to move contents of the block for old key to one of new key.
+ *  the old buffer will not be removed, but might be reused for new buffer.
+ *  it might return -ENOMEM because of memory allocation errors,
+ *  and might return -EIO because of disk read errors.
+ */
+int nilfs_btnode_prepare_change_key(struct address_space *btnc,
+				    struct nilfs_btnode_chkey_ctxt *ctxt)
+{
+	struct buffer_head *obh, *nbh;
+	struct inode *inode = NILFS_BTNC_I(btnc);
+	__u64 oldkey = ctxt->oldkey, newkey = ctxt->newkey;
+	int err;
+
+	if (oldkey == newkey)
+		return 0;
+
+	obh = ctxt->bh;
+	ctxt->newbh = NULL;
+
+	if (inode->i_blkbits == PAGE_SHIFT) {
+		lock_page(obh->b_page);
+		/*
+		 * We cannot call radix_tree_preload for the kernels older
+		 * than 2.6.23, because it is not exported for modules.
+		 */
+retry:
+		err = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
+		if (err)
+			goto failed_unlock;
+		/* BUG_ON(oldkey != obh->b_page->index); */
+		if (unlikely(oldkey != obh->b_page->index))
+			NILFS_PAGE_BUG(obh->b_page,
+				       "invalid oldkey %lld (newkey=%lld)",
+				       (unsigned long long)oldkey,
+				       (unsigned long long)newkey);
+
+		xa_lock_irq(&btnc->i_pages);
+		err = radix_tree_insert(&btnc->i_pages, newkey, obh->b_page);
+		xa_unlock_irq(&btnc->i_pages);
+		/*
+		 * Note: page->index will not change to newkey until
+		 * nilfs_btnode_commit_change_key() will be called.
+		 * To protect the page in intermediate state, the page lock
+		 * is held.
+		 */
+		radix_tree_preload_end();
+		if (!err)
+			return 0;
+		else if (err != -EEXIST)
+			goto failed_unlock;
+
+		err = invalidate_inode_pages2_range(btnc, newkey, newkey);
+		if (!err)
+			goto retry;
+		/* fallback to copy mode */
+		unlock_page(obh->b_page);
+	}
+
+	nbh = nilfs_btnode_create_block(btnc, newkey);
+	if (!nbh)
+		return -ENOMEM;
+
+	BUG_ON(nbh == obh);
+	ctxt->newbh = nbh;
+	return 0;
+
+ failed_unlock:
+	unlock_page(obh->b_page);
+	return err;
+}
+
+/**
+ * nilfs_btnode_commit_change_key
+ *  commit the change_key operation prepared by prepare_change_key().
+ */
+void nilfs_btnode_commit_change_key(struct address_space *btnc,
+				    struct nilfs_btnode_chkey_ctxt *ctxt)
+{
+	struct buffer_head *obh = ctxt->bh, *nbh = ctxt->newbh;
+	__u64 oldkey = ctxt->oldkey, newkey = ctxt->newkey;
+	struct page *opage;
+
+	if (oldkey == newkey)
+		return;
+
+	if (nbh == NULL) {	/* blocksize == pagesize */
+		opage = obh->b_page;
+		if (unlikely(oldkey != opage->index))
+			NILFS_PAGE_BUG(opage,
+				       "invalid oldkey %lld (newkey=%lld)",
+				       (unsigned long long)oldkey,
+				       (unsigned long long)newkey);
+		mark_buffer_dirty(obh);
+
+		xa_lock_irq(&btnc->i_pages);
+		radix_tree_delete(&btnc->i_pages, oldkey);
+		radix_tree_tag_set(&btnc->i_pages, newkey,
+				   PAGECACHE_TAG_DIRTY);
+		xa_unlock_irq(&btnc->i_pages);
+
+		opage->index = obh->b_blocknr = newkey;
+		unlock_page(opage);
+	} else {
+		nilfs_copy_buffer(nbh, obh);
+		mark_buffer_dirty(nbh);
+
+		nbh->b_blocknr = newkey;
+		ctxt->bh = nbh;
+		nilfs_btnode_delete(obh); /* will decrement bh->b_count */
+	}
+}
+
+/**
+ * nilfs_btnode_abort_change_key
+ *  abort the change_key operation prepared by prepare_change_key().
+ */
+void nilfs_btnode_abort_change_key(struct address_space *btnc,
+				   struct nilfs_btnode_chkey_ctxt *ctxt)
+{
+	struct buffer_head *nbh = ctxt->newbh;
+	__u64 oldkey = ctxt->oldkey, newkey = ctxt->newkey;
+
+	if (oldkey == newkey)
+		return;
+
+	if (nbh == NULL) {	/* blocksize == pagesize */
+		xa_lock_irq(&btnc->i_pages);
+		radix_tree_delete(&btnc->i_pages, newkey);
+		xa_unlock_irq(&btnc->i_pages);
+		unlock_page(ctxt->bh->b_page);
+	} else
+		brelse(nbh);
+}