struct socket 简介

本是古典何须时尚 2022-08-28 14:46 14阅读 0赞

### struct socket ###

*  struct socket
 *   *  状态
     *  socket操作函数集合
     *  struct file \*file
     *  struct sock \*sk

# struct socket #

内核版本：2.6.2

socket在内核中的变现形式，也就是我们通常所说的表示层的体现。

struct socket { 
    	socket_state		state;
    	unsigned long		flags;
    	struct proto_ops	*ops;
    	struct fasync_struct	*fasync_list;
    	struct file		*file;
    	struct sock		*sk;
    	wait_queue_head_t	wait;
    	short			type;
    	unsigned char		passcred;
    };

重要字段及其含义。

<table> 
 <thead> 
  <tr> 
   <th>字段</th> 
   <th>含义</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>socket_state state</td> 
   <td>状态</td> 
  </tr> 
  <tr> 
   <td>unsigned long flags</td> 
   <td>socket标志</td> 
  </tr> 
  <tr> 
   <td>struct proto_ops *ops</td> 
   <td>socket操作函数集合</td> 
  </tr> 
  <tr> 
   <td>struct file *file</td> 
   <td>应用层下的表示形式</td> 
  </tr> 
  <tr> 
   <td>struct sock *sk</td> 
   <td>连接层的一个抽象</td> 
  </tr> 
  <tr> 
   <td>short type</td> 
   <td>socket的类型</td> 
  </tr> 
  <tr> 
   <td>wait_queue_head_t</td> 
   <td>缓冲区</td> 
  </tr> 
 </tbody> 
</table>

## 状态 ##

typedef enum { 
    	SS_FREE = 0,			/* not allocated */
    	SS_UNCONNECTED,			/* unconnected to any socket */
    	SS_CONNECTING,			/* in process of connecting */
    	SS_CONNECTED,			/* connected to socket */
    	SS_DISCONNECTING		/* in process of disconnecting */
    } socket_state;

<table> 
 <thead> 
  <tr> 
   <th>字段</th> 
   <th>含义</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>SS_FREE</td> 
   <td>该socket还未分配</td> 
  </tr> 
  <tr> 
   <td>SS_UNCONNECTED</td> 
   <td>未连向任何socket</td> 
  </tr> 
  <tr> 
   <td>SS_CONNECTING</td> 
   <td>正在接连状态</td> 
  </tr> 
  <tr> 
   <td>SS_CONNECTED</td> 
   <td>已连接状态</td> 
  </tr> 
  <tr> 
   <td>SS_DISCONNECTING</td> 
   <td>正在断开连接的过程中</td> 
  </tr> 
 </tbody> 
</table>

该成员只对TCP socket有用，因为只有tcp是面向连接的协议，udp跟raw不需要维护socket状态。

## socket操作函数集合 ##

struct proto_ops { 
    	int		family;
    	struct module	*owner;
    	int		(*release)   (struct socket *sock);
    	int		(*bind)	     (struct socket *sock,
    				      struct sockaddr *myaddr,
    				      int sockaddr_len);
    	int		(*connect)   (struct socket *sock,
    				      struct sockaddr *vaddr,
    				      int sockaddr_len, int flags);
    	int		(*socketpair)(struct socket *sock1,
    				      struct socket *sock2);
    	int		(*accept)    (struct socket *sock,
    				      struct socket *newsock, int flags);
    	int		(*getname)   (struct socket *sock,
    				      struct sockaddr *addr,
    				      int *sockaddr_len, int peer);
    	unsigned int	(*poll)	     (struct file *file, struct socket *sock,
    				      struct poll_table_struct *wait);
    	int		(*ioctl)     (struct socket *sock, unsigned int cmd,
    				      unsigned long arg);
    	int		(*listen)    (struct socket *sock, int len);
    	int		(*shutdown)  (struct socket *sock, int flags);
    	int		(*setsockopt)(struct socket *sock, int level,
    				      int optname, char __user *optval, int optlen);
    	int		(*getsockopt)(struct socket *sock, int level,
    				      int optname, char __user *optval, int __user *optlen);
    	int		(*sendmsg)   (struct kiocb *iocb, struct socket *sock,
    				      struct msghdr *m, size_t total_len);
    	int		(*recvmsg)   (struct kiocb *iocb, struct socket *sock,
    				      struct msghdr *m, size_t total_len,
    				      int flags);
    	int		(*mmap)	     (struct file *file, struct socket *sock,
    				      struct vm_area_struct * vma);
    	ssize_t		(*sendpage)  (struct socket *sock, struct page *page,
    				      int offset, size_t size, int flags);
    };

协议栈中总共定义了三个strcut proto\_ops类型的变量，分别是myinet\_stream\_ops, myinet\_dgram\_ops, myinet\_sockraw\_ops，对应流协议, 数据报和原始套接口协议的操作函数集.

在我们使用使用tcp或者udp等时候时，用的bind，listen，connect等都是上面的函数。

## struct file \*file ##

在我们应用层下，一个socket的表现形式就是一个fd，应为Linux中一切皆为文件，有了文件系统的支持，我们就可以对socket抽象成的fd进行open，write，read等操作。

## struct sock \*sk ##

/** * struct sock - network layer representation of sockets * @__sk_common - shared layout with tcp_tw_bucket * @sk_zapped - ax25 & ipx means !linked * @sk_shutdown - mask of %SEND_SHUTDOWN and/or %RCV_SHUTDOWN * @sk_use_write_queue - wheter to call sk->sk_write_space in sock_wfree * @sk_userlocks - %SO_SNDBUF and %SO_RCVBUF settings * @sk_lock - synchronizer * @sk_rcvbuf - size of receive buffer in bytes * @sk_sleep - sock wait queue * @sk_dst_cache - destination cache * @sk_dst_lock - destination cache lock * @sk_policy - flow policy * @sk_rmem_alloc - receive queue bytes committed * @sk_receive_queue - incoming packets * @sk_wmem_alloc - transmit queue bytes committed * @sk_write_queue - Packet sending queue * @sk_omem_alloc - "o" is "option" or "other" * @sk_wmem_queued - persistent queue size * @sk_forward_alloc - space allocated forward * @sk_allocation - allocation mode * @sk_sndbuf - size of send buffer in bytes * @sk_flags - %SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE, %SO_OOBINLINE settings * @sk_no_check - %SO_NO_CHECK setting, wether or not checkup packets * @sk_debug - %SO_DEBUG setting * @sk_rcvtstamp - %SO_TIMESTAMP setting * @sk_no_largesend - whether to sent large segments or not * @sk_route_caps - route capabilities (e.g. %NETIF_F_TSO) * @sk_lingertime - %SO_LINGER l_linger setting * @sk_hashent - hash entry in several tables (e.g. tcp_ehash) * @sk_pair - socket pair (e.g. AF_UNIX/unix_peer) * @sk_backlog - always used with the per-socket spinlock held * @sk_callback_lock - used with the callbacks in the end of this struct * @sk_error_queue - rarely used * @sk_prot - protocol handlers inside a network family * @sk_err - last error * @sk_err_soft - errors that don't cause failure but are the cause of a persistent failure not just 'timed out' * @sk_ack_backlog - current listen backlog * @sk_max_ack_backlog - listen backlog set in listen() * @sk_priority - %SO_PRIORITY setting * @sk_type - socket type (%SOCK_STREAM, etc) * @sk_localroute - route locally only, %SO_DONTROUTE setting * @sk_protocol - which protocol this socket belongs in this network family * @sk_peercred - %SO_PEERCRED setting * @sk_rcvlowat - %SO_RCVLOWAT setting * @sk_rcvtimeo - %SO_RCVTIMEO setting * @sk_sndtimeo - %SO_SNDTIMEO setting * @sk_filter - socket filtering instructions * @sk_protinfo - private area, net family specific, when not using slab * @sk_slab - the slabcache this instance was allocated from * @sk_timer - sock cleanup timer * @sk_stamp - time stamp of last packet received * @sk_socket - Identd and reporting IO signals * @sk_user_data - RPC layer private data * @sk_owner - module that owns this socket * @sk_state_change - callback to indicate change in the state of the sock * @sk_data_ready - callback to indicate there is data to be processed * @sk_write_space - callback to indicate there is bf sending space available * @sk_error_report - callback to indicate errors (e.g. %MSG_ERRQUEUE) * @sk_backlog_rcv - callback to process the backlog * @sk_destruct - called at sock freeing time, i.e. when all refcnt == 0 */
    struct sock { 
    	/* * Now struct tcp_tw_bucket also uses sock_common, so please just * don't add nothing before this first member (__sk_common) --acme */
    	struct sock_common	__sk_common;
    #define sk_family __sk_common.skc_family
    #define sk_state __sk_common.skc_state
    #define sk_reuse __sk_common.skc_reuse
    #define sk_bound_dev_if __sk_common.skc_bound_dev_if
    #define sk_node __sk_common.skc_node
    #define sk_bind_node __sk_common.skc_bind_node
    #define sk_refcnt __sk_common.skc_refcnt
    	volatile unsigned char	sk_zapped;
    	unsigned char		sk_shutdown;
    	unsigned char		sk_use_write_queue;
    	unsigned char		sk_userlocks;
    	socket_lock_t		sk_lock;
    	int			sk_rcvbuf;
    	wait_queue_head_t	*sk_sleep;
    	struct dst_entry	*sk_dst_cache;
    	rwlock_t		sk_dst_lock;
    	struct xfrm_policy	*sk_policy[2];
    	atomic_t		sk_rmem_alloc;
    	struct sk_buff_head	sk_receive_queue;
    	atomic_t		sk_wmem_alloc;
    	struct sk_buff_head	sk_write_queue;
    	atomic_t		sk_omem_alloc;
    	int			sk_wmem_queued;
    	int			sk_forward_alloc;
    	unsigned int		sk_allocation;
    	int			sk_sndbuf;
    	unsigned long 		sk_flags;
    	char		 	sk_no_check;
    	unsigned char		sk_debug;
    	unsigned char		sk_rcvtstamp;
    	unsigned char		sk_no_largesend;
    	int			sk_route_caps;
    	unsigned long	        sk_lingertime;
    	int			sk_hashent;
    	struct sock		*sk_pair;
    	/* * The backlog queue is special, it is always used with * the per-socket spinlock held and requires low latency * access. Therefore we special case it's implementation. */
    	struct { 
    		struct sk_buff *head;
    		struct sk_buff *tail;
    	} sk_backlog;
    	rwlock_t		sk_callback_lock;
    	struct sk_buff_head	sk_error_queue;
    	struct proto		*sk_prot;
    	int			sk_err,
    				sk_err_soft;
    	unsigned short		sk_ack_backlog;
    	unsigned short		sk_max_ack_backlog;
    	__u32			sk_priority;
    	unsigned short		sk_type;
    	unsigned char		sk_localroute;
    	unsigned char		sk_protocol;
    	struct ucred		sk_peercred;
    	int			sk_rcvlowat;
    	long			sk_rcvtimeo;
    	long			sk_sndtimeo;
    	struct sk_filter      	*sk_filter;
    	void			*sk_protinfo;
    	kmem_cache_t		*sk_slab;
    	struct timer_list	sk_timer;
    	struct timeval		sk_stamp;
    	struct socket		*sk_socket;
    	void			*sk_user_data;
    	struct module		*sk_owner;
    	void			*sk_security;
    	void			(*sk_state_change)(struct sock *sk);
    	void			(*sk_data_ready)(struct sock *sk, int bytes);
    	void			(*sk_write_space)(struct sock *sk);
    	void			(*sk_error_report)(struct sock *sk);
      	int			(*sk_backlog_rcv)(struct sock *sk,
    						  struct sk_buff *skb);  
    	void                    (*sk_destruct)(struct sock *sk);
    };