[PATCH V2 09/10] xfs: Check for extent overflow when remapping an extent

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

Remapping an extent involves unmapping the existing extent and mapping
in the new extent. When unmapping, an extent containing the entire unmap
range can be split into two extents,
i.e. | Old extent | hole | Old extent |
Hence extent count increases by 1.

Mapping in the new extent into the destination file can increase the
extent count by 1.

Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
---
 fs/xfs/libxfs/xfs_inode_fork.h | 15 +++++++++++++++
 fs/xfs/xfs_reflink.c           |  5 +++++
 2 files changed, 20 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
index d750bdff17c9..afff20703270 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.h
+++ b/fs/xfs/libxfs/xfs_inode_fork.h
@@ -85,6 +85,21 @@ struct xfs_ifork {
  * Hence number of extents increases by 2.
  */
 #define XFS_IEXT_REFLINK_END_COW_CNT 2
+/*
+ * Remapping an extent involves unmapping the existing extent and
+ * mapping in the new extent.
+ * When unmapping, an extent containing the entire unmap
+ * range can be split into two extents,
+ * i.e. | Old extent | hole | Old extent |
+ * Hence extent count increases by 1.
+ *
+ * Mapping in the new extent into the destination file can increase
+ * the extent count by 1.
+ */
+#define XFS_IEXT_REFLINK_REMAP_CNT(smap_real, dmap_written) \
+	(((smap_real) ? 1 : 0) + ((dmap_written) ? 1 : 0))
+
+
 /*
  * Fork handling.
  */
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 04a7754ee681..134d49f8c941 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1100,6 +1100,11 @@ xfs_reflink_remap_extent(
 			goto out_cancel;
 	}
 
+	error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
+			XFS_IEXT_REFLINK_REMAP_CNT(smap_real, dmap_written));
+	if (error)
+		goto out_cancel;
+
 	if (smap_real) {
 		/*
 		 * If the extent we're unmapping is backed by storage (written
-- 
2.28.0