X-Git-Url: http://git.cascardo.eti.br/?a=blobdiff_plain;ds=sidebyside;f=fs%2Fext4%2Fext4_extents.h;h=cb1b2c919963290fd10d09ba12f6d8c53ace9fa6;hb=314949321ea821a47d266f2c09168a65aa439b3d;hp=0f58b86e3a0206e19626f361f453aa80b2838857;hpb=af56e0aa35f3ae2a4c1a6d1000702df1dd78cb76;p=cascardo%2Flinux.git

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
@@ -63,8 +63,21 @@
  * 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.