From: Chandan Babu R <redacted>

Source kernel commit: c442f3086d5a108b7ff086c8ade1923a8f389db5

A write to a sub-interval of an existing unwritten extent causes
the original extent to be split into 3 extents
i.e. | Unwritten | Real | Unwritten |
Hence extent count can increase by 2.

Reviewed-by: Darrick J. Wong <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Henderson <redacted>
Signed-off-by: Chandan Babu R <redacted>
Signed-off-by: Darrick J. Wong <redacted>
Signed-off-by: Allison Henderson <redacted>
---
 libxfs/xfs_inode_fork.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/libxfs/xfs_inode_fork.h b/libxfs/xfs_inode_fork.h
index 8d89838..917e289 100644
--- a/libxfs/xfs_inode_fork.h
+++ b/libxfs/xfs_inode_fork.h

@@ -71,6 +71,15 @@ struct xfs_ifork {
 	(XFS_DA_NODE_MAXDEPTH + max(1, rmt_blks))
 
 /*
+ * A write to a sub-interval of an existing unwritten extent causes the original
+ * extent to be split into 3 extents
+ * i.e. | Unwritten | Real | Unwritten |
+ * Hence extent count can increase by 2.
+ */
+#define XFS_IEXT_WRITE_UNWRITTEN_CNT	(2)
+
+
+/*
  * Fork handling.
  */
 

-- 
2.7.4