diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index ed8da62..4d759a5 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -914,3 +914,428 @@ xfs_reflink_recover_cow(
 
 	return error;
 }
+
+/*
+ * Reflinking (Block) Ranges of Two Files Together
+ *
+ * First, ensure that the reflink flag is set on both inodes.  The flag is an
+ * optimization to avoid unnecessary refcount btree lookups in the write path.
+ *
+ * Now we can iteratively remap the range of extents (and holes) in src to the
+ * corresponding ranges in dest.  Let drange and srange denote the ranges of
+ * logical blocks in dest and src touched by the reflink operation.
+ *
+ * While the length of drange is greater than zero,
+ *    - Read src's bmbt at the start of srange ("imap")
+ *    - If imap doesn't exist, make imap appear to start at the end of srange
+ *      with zero length.
+ *    - If imap starts before srange, advance imap to start at srange.
+ *    - If imap goes beyond srange, truncate imap to end at the end of srange.
+ *    - Punch (imap start - srange start + imap len) blocks from dest at
+ *      offset (drange start).
+ *    - If imap points to a real range of pblks,
+ *         > Increase the refcount of the imap's pblks
+ *         > Map imap's pblks into dest at the offset
+ *           (drange start + imap start - srange start)
+ *    - Advance drange and srange by (imap start - srange start + imap len)
+ *
+ * Finally, if the reflink made dest longer, update both the in-core and
+ * on-disk file sizes.
+ *
+ * ASCII Art Demonstration:
+ *
+ * Let's say we want to reflink this source file:
+ *
+ * ----SSSSSSS-SSSSS----SSSSSS (src file)
+ *   <-------------------->
+ *
+ * into this destination file:
+ *
+ * --DDDDDDDDDDDDDDDDDDD--DDD (dest file)
+ *        <-------------------->
+ * '-' means a hole, and 'S' and 'D' are written blocks in the src and dest.
+ * Observe that the range has different logical offsets in either file.
+ *
+ * Consider that the first extent in the source file doesn't line up with our
+ * reflink range.  Unmapping  and remapping are separate operations, so we can
+ * unmap more blocks from the destination file than we remap.
+ *
+ * ----SSSSSSS-SSSSS----SSSSSS
+ *   <------->
+ * --DDDDD---------DDDDD--DDD
+ *        <------->
+ *
+ * Now remap the source extent into the destination file:
+ *
+ * ----SSSSSSS-SSSSS----SSSSSS
+ *   <------->
+ * --DDDDD--SSSSSSSDDDDD--DDD
+ *        <------->
+ *
+ * Do likewise with the second hole and extent in our range.  Holes in the
+ * unmap range don't affect our operation.
+ *
+ * ----SSSSSSS-SSSSS----SSSSSS
+ *            <---->
+ * --DDDDD--SSSSSSS-SSSSS-DDD
+ *                 <---->
+ *
+ * Finally, unmap and remap part of the third extent.  This will increase the
+ * size of the destination file.
+ *
+ * ----SSSSSSS-SSSSS----SSSSSS
+ *                  <----->
+ * --DDDDD--SSSSSSS-SSSSS----SSS
+ *                       <----->
+ *
+ * Once we update the destination file's i_size, we're done.
+ */
+
+/*
+ * Ensure the reflink bit is set in both inodes.
+ */
+STATIC int
+xfs_reflink_set_inode_flag(
+	struct xfs_inode	*src,
+	struct xfs_inode	*dest)
+{
+	struct xfs_mount	*mp = src->i_mount;
+	int			error;
+	struct xfs_trans	*tp;
+
+	if (xfs_is_reflink_inode(src) && xfs_is_reflink_inode(dest))
+		return 0;
+
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
+	if (error)
+		goto out_error;
+
+	/* Lock both files against IO */
+	if (src->i_ino == dest->i_ino)
+		xfs_ilock(src, XFS_ILOCK_EXCL);
+	else
+		xfs_lock_two_inodes(src, dest, XFS_ILOCK_EXCL);
+
+	if (!xfs_is_reflink_inode(src)) {
+		trace_xfs_reflink_set_inode_flag(src);
+		xfs_trans_ijoin(tp, src, XFS_ILOCK_EXCL);
+		src->i_d.di_flags2 |= XFS_DIFLAG2_REFLINK;
+		xfs_trans_log_inode(tp, src, XFS_ILOG_CORE);
+		xfs_ifork_init_cow(src);
+	} else
+		xfs_iunlock(src, XFS_ILOCK_EXCL);
+
+	if (src->i_ino == dest->i_ino)
+		goto commit_flags;
+
+	if (!xfs_is_reflink_inode(dest)) {
+		trace_xfs_reflink_set_inode_flag(dest);
+		xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
+		dest->i_d.di_flags2 |= XFS_DIFLAG2_REFLINK;
+		xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
+		xfs_ifork_init_cow(dest);
+	} else
+		xfs_iunlock(dest, XFS_ILOCK_EXCL);
+
+commit_flags:
+	error = xfs_trans_commit(tp);
+	if (error)
+		goto out_error;
+	return error;
+
+out_error:
+	trace_xfs_reflink_set_inode_flag_error(dest, error, _RET_IP_);
+	return error;
+}
+
+/*
+ * Update destination inode size, if necessary.
+ */
+STATIC int
+xfs_reflink_update_dest(
+	struct xfs_inode	*dest,
+	xfs_off_t		newlen)
+{
+	struct xfs_mount	*mp = dest->i_mount;
+	struct xfs_trans	*tp;
+	int			error;
+
+	if (newlen <= i_size_read(VFS_I(dest)))
+		return 0;
+
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
+	if (error)
+		goto out_error;
+
+	xfs_ilock(dest, XFS_ILOCK_EXCL);
+	xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
+
+	trace_xfs_reflink_update_inode_size(dest, newlen);
+	i_size_write(VFS_I(dest), newlen);
+	dest->i_d.di_size = newlen;
+	xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
+
+	error = xfs_trans_commit(tp);
+	if (error)
+		goto out_error;
+	return error;
+
+out_error:
+	trace_xfs_reflink_update_inode_size_error(dest, error, _RET_IP_);
+	return error;
+}
+
+/*
+ * Unmap a range of blocks from a file, then map other blocks into the hole.
+ * The range to unmap is (destoff : destoff + srcioff + irec->br_blockcount).
+ * The extent irec is mapped into dest at irec->br_startoff.
+ */
+STATIC int
+xfs_reflink_remap_extent(
+	struct xfs_inode	*ip,
+	struct xfs_bmbt_irec	*irec,
+	xfs_fileoff_t		destoff,
+	xfs_off_t		new_isize)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_trans	*tp;
+	xfs_fsblock_t		firstfsb;
+	unsigned int		resblks;
+	struct xfs_defer_ops	dfops;
+	struct xfs_bmbt_irec	uirec;
+	bool			real_extent;
+	xfs_filblks_t		rlen;
+	xfs_filblks_t		unmap_len;
+	xfs_off_t		newlen;
+	int			error;
+
+	unmap_len = irec->br_startoff + irec->br_blockcount - destoff;
+	trace_xfs_reflink_punch_range(ip, destoff, unmap_len);
+
+	/* Only remap normal extents. */
+	real_extent =  (irec->br_startblock != HOLESTARTBLOCK &&
+			irec->br_startblock != DELAYSTARTBLOCK &&
+			!ISUNWRITTEN(irec));
+
+	/* Start a rolling transaction to switch the mappings */
+	resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);
+	if (error)
+		goto out;
+
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	xfs_trans_ijoin(tp, ip, 0);
+
+	/* If we're not just clearing space, then do we have enough quota? */
+	if (real_extent) {
+		error = xfs_trans_reserve_quota_nblks(tp, ip,
+				irec->br_blockcount, 0, XFS_QMOPT_RES_REGBLKS);
+		if (error)
+			goto out_cancel;
+	}
+
+	trace_xfs_reflink_remap(ip, irec->br_startoff,
+				irec->br_blockcount, irec->br_startblock);
+
+	/* Unmap the old blocks in the data fork. */
+	rlen = unmap_len;
+	while (rlen) {
+		xfs_defer_init(&dfops, &firstfsb);
+		error = __xfs_bunmapi(tp, ip, destoff, &rlen, 0, 1,
+				&firstfsb, &dfops);
+		if (error)
+			goto out_defer;
+
+		/* Trim the extent to whatever got unmapped. */
+		uirec = *irec;
+		xfs_trim_extent(&uirec, destoff + rlen, unmap_len - rlen);
+		unmap_len = rlen;
+
+		/* If this isn't a real mapping, we're done. */
+		if (!real_extent || uirec.br_blockcount == 0)
+			goto next_extent;
+
+		trace_xfs_reflink_remap(ip, uirec.br_startoff,
+				uirec.br_blockcount, uirec.br_startblock);
+
+		/* Update the refcount tree */
+		error = xfs_refcount_increase_extent(mp, &dfops, &uirec);
+		if (error)
+			goto out_defer;
+
+		/* Map the new blocks into the data fork. */
+		error = xfs_bmap_map_extent(mp, &dfops, ip, XFS_DATA_FORK,
+				&uirec);
+		if (error)
+			goto out_defer;
+
+		/* Update quota accounting. */
+		xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_BCOUNT,
+				uirec.br_blockcount);
+
+		/* Update dest isize if needed. */
+		newlen = XFS_FSB_TO_B(mp,
+				uirec.br_startoff + uirec.br_blockcount);
+		newlen = min_t(xfs_off_t, newlen, new_isize);
+		if (newlen > i_size_read(VFS_I(ip))) {
+			trace_xfs_reflink_update_inode_size(ip, newlen);
+			i_size_write(VFS_I(ip), newlen);
+			ip->i_d.di_size = newlen;
+			xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
+		}
+
+next_extent:
+		/* Process all the deferred stuff. */
+		error = xfs_defer_finish(&tp, &dfops, ip);
+		if (error)
+			goto out_defer;
+	}
+
+	error = xfs_trans_commit(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	if (error)
+		goto out;
+	return 0;
+
+out_defer:
+	xfs_defer_cancel(&dfops);
+out_cancel:
+	xfs_trans_cancel(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+out:
+	trace_xfs_reflink_remap_extent_error(ip, error, _RET_IP_);
+	return error;
+}
+
+/*
+ * Iteratively remap one file's extents (and holes) to another's.
+ */
+STATIC int
+xfs_reflink_remap_blocks(
+	struct xfs_inode	*src,
+	xfs_fileoff_t		srcoff,
+	struct xfs_inode	*dest,
+	xfs_fileoff_t		destoff,
+	xfs_filblks_t		len,
+	xfs_off_t		new_isize)
+{
+	struct xfs_bmbt_irec	imap;
+	int			nimaps;
+	int			error = 0;
+	xfs_filblks_t		range_len;
+
+	/* drange = (destoff, destoff + len); srange = (srcoff, srcoff + len) */
+	while (len) {
+		trace_xfs_reflink_remap_blocks_loop(src, srcoff, len,
+				dest, destoff);
+		/* Read extent from the source file */
+		nimaps = 1;
+		xfs_ilock(src, XFS_ILOCK_EXCL);
+		error = xfs_bmapi_read(src, srcoff, len, &imap, &nimaps, 0);
+		xfs_iunlock(src, XFS_ILOCK_EXCL);
+		if (error)
+			goto err;
+		ASSERT(nimaps == 1);
+
+		trace_xfs_reflink_remap_imap(src, srcoff, len, XFS_IO_OVERWRITE,
+				&imap);
+
+		/* Translate imap into the destination file. */
+		range_len = imap.br_startoff + imap.br_blockcount - srcoff;
+		imap.br_startoff += destoff - srcoff;
+
+		/* Clear dest from destoff to the end of imap and map it in. */
+		error = xfs_reflink_remap_extent(dest, &imap, destoff,
+				new_isize);
+		if (error)
+			goto err;
+
+		if (fatal_signal_pending(current)) {
+			error = -EINTR;
+			goto err;
+		}
+
+		/* Advance drange/srange */
+		srcoff += range_len;
+		destoff += range_len;
+		len -= range_len;
+	}
+
+	return 0;
+
+err:
+	trace_xfs_reflink_remap_blocks_error(dest, error, _RET_IP_);
+	return error;
+}
+
+/*
+ * Link a range of blocks from one file to another.
+ */
+int
+xfs_reflink_remap_range(
+	struct xfs_inode	*src,
+	xfs_off_t		srcoff,
+	struct xfs_inode	*dest,
+	xfs_off_t		destoff,
+	xfs_off_t		len)
+{
+	struct xfs_mount	*mp = src->i_mount;
+	xfs_fileoff_t		sfsbno, dfsbno;
+	xfs_filblks_t		fsblen;
+	int			error;
+
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return -EOPNOTSUPP;
+
+	if (XFS_FORCED_SHUTDOWN(mp))
+		return -EIO;
+
+	/* Don't reflink realtime inodes */
+	if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
+		return -EINVAL;
+
+	trace_xfs_reflink_remap_range(src, srcoff, len, dest, destoff);
+
+	/* Lock both files against IO */
+	if (src->i_ino == dest->i_ino) {
+		xfs_ilock(src, XFS_IOLOCK_EXCL);
+		xfs_ilock(src, XFS_MMAPLOCK_EXCL);
+	} else {
+		xfs_lock_two_inodes(src, dest, XFS_IOLOCK_EXCL);
+		xfs_lock_two_inodes(src, dest, XFS_MMAPLOCK_EXCL);
+	}
+
+	error = xfs_reflink_set_inode_flag(src, dest);
+	if (error)
+		goto out_error;
+
+	/*
+	 * Invalidate the page cache so that we can clear any CoW mappings
+	 * in the destination file.
+	 */
+	truncate_inode_pages_range(&VFS_I(dest)->i_data, destoff,
+				   PAGE_ALIGN(destoff + len) - 1);
+
+	dfsbno = XFS_B_TO_FSBT(mp, destoff);
+	sfsbno = XFS_B_TO_FSBT(mp, srcoff);
+	fsblen = XFS_B_TO_FSB(mp, len);
+	error = xfs_reflink_remap_blocks(src, sfsbno, dest, dfsbno, fsblen,
+			destoff + len);
+	if (error)
+		goto out_error;
+
+	error = xfs_reflink_update_dest(dest, destoff + len);
+	if (error)
+		goto out_error;
+
+out_error:
+	xfs_iunlock(src, XFS_MMAPLOCK_EXCL);
+	xfs_iunlock(src, XFS_IOLOCK_EXCL);
+	if (src->i_ino != dest->i_ino) {
+		xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
+		xfs_iunlock(dest, XFS_IOLOCK_EXCL);
+	}
+	if (error)
+		trace_xfs_reflink_remap_range_error(dest, error, _RET_IP_);
+	return error;
+}
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index 79b00a9..bd9c832 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -44,5 +44,7 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset,
 extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t count);
 extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
+extern int xfs_reflink_remap_range(struct xfs_inode *src, xfs_off_t srcoff,
+		struct xfs_inode *dest, xfs_off_t destoff, xfs_off_t len);
 
 #endif /* __XFS_REFLINK_H */
