[PATCH V2 08/10] xfs: Check for extent overflow when moving extent from cow to data fork

[Chandan Babu R <chandanrlinux@gmail.com>]

Moving an extent to data fork can cause a sub-interval of an existing
extent to be unmapped. This will increase extent count by 1. Mapping in
the new extent can increase the extent count by 1 again i.e.
 | Old extent | New extent | Old extent |
Hence number of extents increases by 2.

Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
---
 fs/xfs/libxfs/xfs_inode_fork.h | 10 +++++++++-
 fs/xfs/xfs_reflink.c           |  6 ++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
index 63f83a13e0a8..d750bdff17c9 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.h
+++ b/fs/xfs/libxfs/xfs_inode_fork.h
@@ -76,7 +76,15 @@ struct xfs_ifork {
  * increase by 1.
  */
 #define XFS_IEXT_INSERT_HOLE_CNT 1
-
+/*
+ * Moving an extent to data fork can cause a sub-interval of an
+ * existing extent to be unmapped. This will increase extent count by
+ * 1. Mapping in the new extent can increase the extent count by 1
+ * again i.e.
+ * | Old extent | New extent | Old extent |
+ * Hence number of extents increases by 2.
+ */
+#define XFS_IEXT_REFLINK_END_COW_CNT 2
 /*
  * Fork handling.
  */
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index aac83f9d6107..04a7754ee681 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -29,6 +29,7 @@
 #include "xfs_iomap.h"
 #include "xfs_sb.h"
 #include "xfs_ag_resv.h"
+#include "xfs_trans_resv.h"
 
 /*
  * Copy on Write of Shared Blocks
@@ -628,6 +629,11 @@ xfs_reflink_end_cow_extent(
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, ip, 0);
 
+	error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
+			XFS_IEXT_REFLINK_END_COW_CNT);
+	if (error)
+		goto out_cancel;
+
 	/*
 	 * In case of racing, overlapping AIO writes no COW extents might be
 	 * left by the time I/O completes for the loser of the race.  In that
-- 
2.28.0