xfs: recognize the reflink feature bit

Add the reflink feature flag to the set of recognized feature flags.
This enables users to write to reflink filesystems.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 15b9fcd..72bde281 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1614,6 +1614,9 @@
 			"DAX unsupported by block device. Turning off DAX.");
 			mp->m_flags &= ~XFS_MOUNT_DAX;
 		}
+		if (xfs_sb_version_hasreflink(&mp->m_sb))
+			xfs_alert(mp,
+		"DAX and reflink have not been tested together!");
 	}
 
 	if (xfs_sb_version_hasrmapbt(&mp->m_sb)) {
@@ -1627,6 +1630,10 @@
 	"EXPERIMENTAL reverse mapping btree feature enabled. Use at your own risk!");
 	}
 
+	if (xfs_sb_version_hasreflink(&mp->m_sb))
+		xfs_alert(mp,
+	"EXPERIMENTAL reflink feature enabled. Use at your own risk!");
+
 	error = xfs_mountfs(mp);
 	if (error)
 		goto out_filestream_unmount;