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-rw-r--r--fs/ext4/ext4_extents.h24
1 files changed, 24 insertions, 0 deletions
diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index 0f58b86e3a02..cb1b2c919963 100644
--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -63,9 +63,22 @@
* ext4_inode has i_block array (60 bytes total).
* The first 12 bytes store ext4_extent_header;
* the remainder stores an array of ext4_extent.
+ * For non-inode extent blocks, ext4_extent_tail
+ * follows the array.
*/
/*
+ * This is the extent tail on-disk structure.
+ * All other extent structures are 12 bytes long. It turns out that
+ * block_size % 12 >= 4 for at least all powers of 2 greater than 512, which
+ * covers all valid ext4 block sizes. Therefore, this tail structure can be
+ * crammed into the end of the block without having to rebalance the tree.
+ */
+struct ext4_extent_tail {
+ __le32 et_checksum; /* crc32c(uuid+inum+extent_block) */
+};
+
+/*
* This is the extent on-disk structure.
* It's used at the bottom of the tree.
*/
@@ -101,6 +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.