[PATCH V7 06/14] xfs: Check for extent overflow when writing to unwritten extent

Chandan Babu R
2020-10-19T06:41:30Z

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 <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
---
fs/xfs/libxfs/xfs_inode_fork.h | 8 ++++++++
fs/xfs/xfs_iomap.c | 5 +++++
2 files changed, 13 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
index fd93fdc67ee4..afb647e1e3fa 100644
--- a/fs/xfs/libxfs/xfs_inode_fork.h
+++ b/fs/xfs/libxfs/xfs_inode_fork.h
@@ -70,6 +70,14 @@ struct xfs_ifork {
#define XFS_IEXT_DIR_MANIP_CNT(mp) \
((XFS_DA_NODE_MAXDEPTH + 1 + 1) * (mp)->m_dir_geo->fsbcount)

+/*
+ * 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.
*/
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index a302a96823b8..2aa788379611 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -566,6 +566,11 @@ xfs_iomap_write_unwritten(
if (error)
goto error_on_bmapi_transaction;

+ error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
+ XFS_IEXT_WRITE_UNWRITTEN_CNT);
+ if (error)
+ goto error_on_bmapi_transaction;
+
/*
* Modify the unwritten extent state of the buffer.
*/
--
2.28.0