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

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3c20de1..bcc634b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -811,6 +811,8 @@
 	__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 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;
 

fs/ext4/extents_status.h

diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h
new file mode 100644
index 0000000..8be2ab9
--- /dev/null
+++ b/fs/ext4/extents_status.h
@@ -0,0 +1,25 @@
+/*
+ *  fs/ext4/extents_status.h
+ *
+ * Written by Yongqiang Yang <xiaoqiangnk@gmail.com>
+ * Modified by
+ *	Allison Henderson <achender@linux.vnet.ibm.com>
+ *	Zheng Liu <wenqing.lz@taobao.com>
+ *
+ */
+
+#ifndef _EXT4_EXTENTS_STATUS_H
+#define _EXT4_EXTENTS_STATUS_H
+
+struct extent_status {
+	struct rb_node rb_node;
+	ext4_lblk_t start;	/* first block extent covers */
+	ext4_lblk_t len;	/* length of extent in block */
+};
+
+struct ext4_es_tree {
+	struct rb_root root;
+	struct extent_status *cache_es;	/* recently accessed extent */
+};
+
+#endif /* _EXT4_EXTENTS_STATUS_H */