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node是f2fs重要的管理结构, 它非常重要! 系统挂载完毕后, 会有一个f2fs_nm_info结构的node管理器来管理node的分配. f2fs_nm_info中最让人疑惑的是几颗基数树:
490 struct f2fs_nm_info { 491 block_t nat_blkaddr; /* base disk address of NAT */ 492 nid_t max_nid; /* maximum possible node ids */ 494 nid_t next_scan_nid; /* the next nid to be scanned */ 497 /* NAT cache management */ 498 struct radix_tree_root nat_root;/* root of the nat entry cache */ 499 struct radix_tree_root nat_set_root;/* root of the nat set cache */ 501 struct list_head nat_entries; /* cached nat entry list (clean) */ 502 unsigned int nat_cnt; /* the # of cached nat entries */ 503 unsigned int dirty_nat_cnt; /* total num of nat entries in set */ 505 /* free node ids management */ 506 struct radix_tree_root free_nid_root;/* root of the free_nid cache */ 507 struct list_head free_nid_list; /* a list for free nids */ 509 unsigned int fcnt; /* the number of free node id */ 512 /* for checkpoint */ 513 char *nat_bitmap; /* NAT bitmap pointer */ 514 int bitmap_size; /* bitmap size */ 515 };
三棵基数树分别是: nat_root, nat_set_root, free_nid_root;
首先, 对于整个node管理器来说, 一个核心的结构体是node_info:
46 struct node_info { 47 nid_t nid; /* node id */ 48 nid_t ino; /* inode number of the node‘s owner */ 49 block_t blk_addr; /* block address of the node */ 50 unsigned char version; /* version of the node */ 51 unsigned char flag; /* for node information bits */ 52 }; 53 54 struct nat_entry { 55 struct list_head list; /* for clean or dirty nat list */ 56 struct node_info ni; /* in-memory node information */ 57 };
发现node_info和f2fs_nat_entry【磁盘上的存储】长得太像了, 甚至比 struct f2fs_nat_entry 还要多出来一个flag 位来表示这个节点的一些属性！
266 struct f2fs_nat_entry {
267 __u8 version; /* latest version of cached nat entry */ 268 __le32 ino; /* inode number */ 269 __le32 block_addr; /* block address */ 270 } __packed;
这个core数据结构被两个结构控制：一个是基数树【负责索引】，一个是链表。
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原文地址：http://www.cnblogs.com/honpey/p/4946128.html
