f2fs源码解析(五) node管理结构梳理

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:

  struct f2fs_nm_info {
      block_t nat_blkaddr;        /* base disk address of NAT */
      nid_t max_nid;          /* maximum possible node ids */
      nid_t next_scan_nid;        /* the next nid to be scanned */
      /* NAT cache management */
      struct radix_tree_root nat_root;/* root of the nat entry cache */
      struct radix_tree_root nat_set_root;/* root of the nat set cache */
      struct list_head nat_entries;   /* cached nat entry list (clean) */
      unsigned int nat_cnt;       /* the # of cached nat entries */
      unsigned int dirty_nat_cnt; /* total num of nat entries in set */
      /* free node ids management */
      struct radix_tree_root free_nid_root;/* root of the free_nid cache */
      struct list_head free_nid_list; /* a list for free nids */
      unsigned int fcnt;      /* the number of free node id */
      /* for checkpoint */
      char *nat_bitmap;       /* NAT bitmap pointer */
      int bitmap_size;        /* bitmap size */
  };

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:

  struct node_info {
      nid_t nid;      /* node id */
      nid_t ino;      /* inode number of the node's owner */
      block_t blk_addr;   /* block address of the node */
      unsigned char version;  /* version of the node */
      unsigned char flag; /* for node information bits */
  };   

  struct nat_entry {
      struct list_head list;  /* for clean or dirty nat list */
      struct node_info ni;    /* in-memory node information */
  };

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 */
     __le32 ino;     /* inode number */
     __le32 block_addr;  /* block address */
 } __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。