ext4: verify and calculate checksums for extent tree blocks

Calculate and verify the checksum for each extent tree block.  The
checksum is located in the space immediately after the last possible
ext4_extent in the block.  The space is is typically the last 4-8
bytes in the block.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index 94822e74ef73..cb1b2c919963 100644
--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -114,6 +114,17 @@ struct ext4_extent_header {
 
 #define EXT4_EXT_MAGIC          cpu_to_le16(0xf30a)
 
+#define EXT4_EXTENT_TAIL_OFFSET(hdr) \
+        (sizeof(struct ext4_extent_header) + \
+         (sizeof(struct ext4_extent) * le16_to_cpu((hdr)->eh_max)))
+
+static inline struct ext4_extent_tail *
+find_ext4_extent_tail(struct ext4_extent_header *eh)
+{
+        return (struct ext4_extent_tail *)(((void *)eh) +
+                                           EXT4_EXTENT_TAIL_OFFSET(eh));
+}
+
 /*
  * Array of ext4_ext_path contains path to some extent.
  * Creation/lookup routines use it for traversal/splitting/etc.