linux l2tp kernel（包含了L2TPv3的版本）主要数据结构理解

主要结构体

 原来的注释就挺全的，就不多废话了，无非就是通过指针相互指，通过全局的hash保存。

1

struct l2tp_net {struct list_head l2tp_tunnel_list; //保存了所有tunnel的双向列表的表头spinlock_t l2tp_tunnel_list_lock;struct hlist_head l2tp_session_hlist[L2TP_HASH_SIZE_2]; /*保存了所有的session的hash列表的表头偏移量由hash_32计算，此处的size（1<<8）更大，hash冲突比tunnel结构体里的小(1<<4)（不过一个tunnel基本上也不会包含很多个session,具体请参考hash_32的实现），通过调用RCU的api方式访问*/spinlock_t l2tp_session_hlist_lock;};

2

struct l2tp_tunnel {intmagic;/* Should be L2TP_TUNNEL_MAGIC */rwlock_thlist_lock;/* protect session_hlist */struct hlist_headsession_hlist[L2TP_HASH_SIZE]; //size比较下，是1<<4/* hashed list of sessions, * hashed by id */u32tunnel_id;u32peer_tunnel_id;intversion;/* 2=>L2TPv2, 3=>L2TPv3 */charname[20];/* for logging */ //"tunl %u"intdebug;/* bitmask of debug message * categories */enum l2tp_encap_typeencap;struct l2tp_statsstats;struct list_headlist;/* Keep a list of all tunnels */ //双向链接到l2tp_net结构体的l2tp_tunnel_list列表中，见上struct net*l2tp_net;/* the net we belong to */atomic_tref_count;#ifdef CONFIG_DEBUG_FSvoid (*show)(struct seq_file *m, void *arg);#endifint (*recv_payload_hook)(struct sk_buff *skb);void (*old_sk_destruct)(struct sock *);struct sock*sock;/* Parent socket */intfd;uint8_tpriv[0];/* private data */};

3

struct l2tp_session {intmagic;/* should be * L2TP_SESSION_MAGIC */struct l2tp_tunnel*tunnel;/* back pointer to tunnel * context */ //指向所属tunnelu32session_id;u32peer_session_id;u8cookie[8];intcookie_len;u8peer_cookie[8];intpeer_cookie_len;u16offset;/* offset from end of L2TP header   to beginning of data */u16l2specific_len;u16l2specific_type;u16hdr_len;u32nr;/* session NR state (receive) */u32ns;/* session NR state (send) */struct sk_buff_headreorder_q;/* receive reorder queue */struct hlist_nodehlist;/* Hash list node */ //链接到l2tp_tunnel结构体的sesson_hlist中，见上atomic_tref_count;charname[32];/* for logging */charifname[IFNAMSIZ];unsigneddata_seq:2;/* data sequencing level * 0 => none, 1 => IP only, * 2 => all */unsignedrecv_seq:1;/* expect receive packets with * sequence numbers? */unsignedsend_seq:1;/* send packets with sequence * numbers? */unsignedlns_mode:1;/* behave as LNS? LAC enables * sequence numbers under * control of LNS. */intdebug;/* bitmask of debug message * categories */intreorder_timeout; /* configured reorder timeout  * (in jiffies) */intmtu;intmru;enum l2tp_pwtypepwtype;struct l2tp_statsstats;struct hlist_nodeglobal_hlist;/* Global hash list node */ //链接到l2tp_net结构体的l2tp_session_hlist中，见上int (*build_header)(struct l2tp_session *session, void *buf);void (*recv_skb)(struct l2tp_session *session, struct sk_buff *skb, int data_len);void (*session_close)(struct l2tp_session *session);void (*ref)(struct l2tp_session *session);void (*deref)(struct l2tp_session *session);#if defined(CONFIG_L2TP_DEBUGFS) || defined(CONFIG_L2TP_DEBUGFS_MODULE)void (*show)(struct seq_file *m, void *priv);#endifuint8_tpriv[0];/* private data */};

4

/* Private data of each session. This data lives at the end of struct * l2tp_session, referenced via session->priv[]. 即处于上面结构体l2tp_session的最后部分，通过l2tp_session_priv(struct l2tp_session session)返回相应的地址指针，这里是上层承载ppp的包 */struct pppol2tp_session {intowner;/* pid that opened the socket */struct sock*sock;/* Pointer to the session * PPPoX socket */struct sock*tunnel_sock;/* Pointer to the tunnel UDP * socket */intflags;/* accessed by PPPIOCGFLAGS. * Unused. */};