@@ -37,6 +37,8 @@
 #include "xfs_alloc.h"
 #include "xfs_bit.h"
 #include "xfs_fsmap.h"
+#include "xfs_refcount.h"
+#include "xfs_refcount_btree.h"
 
 /* Convert an xfs_fsmap to an fsmap. */
 void

@@ -192,6 +194,42 @@ xfs_getfsmap_rec_before_low_key(
 	return false;
 }
 
+/* Decide if this mapping is shared. */
+STATIC int
+xfs_getfsmap_is_shared(
+	struct xfs_mount		*mp,
+	struct xfs_getfsmap_info	*info,
+	struct xfs_rmap_irec		*rec,
+	bool				*stat)
+{
+	struct xfs_btree_cur		*cur;
+	xfs_agblock_t			fbno;
+	xfs_extlen_t			flen;
+	int				error;
+
+	*stat = false;
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return 0;
+	/* rt files will have agno set to NULLAGNUMBER */
+	if (info->agno == NULLAGNUMBER)
+		return 0;
+
+	/* Are there any shared blocks here? */
+	flen = 0;
+	cur = xfs_refcountbt_init_cursor(mp, NULL, info->agf_bp,
+			info->agno, NULL);
+
+	error = xfs_refcount_find_shared(cur, rec->rm_startblock,
+			rec->rm_blockcount, &fbno, &flen, false);
+
+	xfs_btree_del_cursor(cur, error ? XFS_BTREE_ERROR : XFS_BTREE_NOERROR);
+	if (error)
+		return error;
+
+	*stat = flen > 0;
+	return 0;
+}
+
 /*
  * Format a reverse mapping for getfsmap, having translated rm_startblock
  * into the appropriate daddr units.

@@ -205,6 +243,7 @@ xfs_getfsmap_helper(
 {
 	struct xfs_fsmap		fmr;
 	xfs_daddr_t			key_end;
+	bool				shared;
 	int				error;
 
 	/*

@@ -304,6 +343,13 @@ xfs_getfsmap_helper(
 		fmr.fmr_flags |= FMR_OF_ATTR_FORK;
 	if (rec->rm_flags & XFS_RMAP_BMBT_BLOCK)
 		fmr.fmr_flags |= FMR_OF_EXTENT_MAP;
+	if (fmr.fmr_flags == 0) {
+		error = xfs_getfsmap_is_shared(mp, info, rec, &shared);
+		if (error)
+			return error;
+		if (shared)
+			fmr.fmr_flags |= FMR_OF_SHARED;
+	}
 	error = info->formatter(&fmr, info->format_arg);
 	if (error)
 		return error;