ext4: add data structures for the extent status tree

This patch adds two structures that supports extent status tree, extent_status
and ext4_es_tree.  Currently extent_status is used to track a delay extent for
an inode, which record the start block and the length of the delay extent.
ext4_es_tree is used to store all extent_status for an inode in memory.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: Allison Henderson <achender@linux.vnet.ibm.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -811,6 +811,8 @@ struct ext4_ext_cache {
 	__u32		ec_len; /* must be 32bit to return holes */
 };
 
+#include "extents_status.h"
+
 /*
  * fourth extended file system inode data in memory
  */
@@ -888,6 +890,10 @@ struct ext4_inode_info {
 	struct list_head i_prealloc_list;
 	spinlock_t i_prealloc_lock;
 
+	/* extents status tree */
+	struct ext4_es_tree i_es_tree;
+	rwlock_t i_es_lock;
+
 	/* ialloc */
 	ext4_group_t	i_last_alloc_group;