六、系统网络状态相关的数据结构

6.1 ifconf

• \linux-2.6.32.63\include\linux\if.h

/* Structure used in SIOCGIFCONF request.  Used to retrieve interface
   configuration for machine (useful for programs which must know all
   networks accessible).  
*/ 
struct ifconf
{
    int ifc_len;        	// Size of buffer.   
    union
    {
    __caddr_t ifcu_buf;
    struct ifreq *ifcu_req;    //保存每块网卡的具体信息的结构体数组
    } ifc_ifcu;
};
#define ifc_buf    ifc_ifcu.ifcu_buf   /* Buffer address.  */
#define ifc_req    ifc_ifcu.ifcu_req   /* Array of structures.  */
#define _IOT_ifconf _IOT(_IOTS(struct ifconf),1,0,0,0,0) /* not right */

6.2 ifreq

• \linux-2.6.32.63\include\linux\if.h

/*
 * Interface request structure used for socket
 * ioctl's.  All interface ioctl's must have parameter
 * definitions which begin with ifr_name.  The
 * remainder may be interface specific.
*/
struct ifreq 
{
#define IFHWADDRLEN    6
    union
    {
        char    ifrn_name[IFNAMSIZ];        /* if name, e.g. "en0" */
    } ifr_ifrn;
    
    //描述套接口的地址结构
    union 
    {
        struct    sockaddr ifru_addr;
        struct    sockaddr ifru_dstaddr;
        struct    sockaddr ifru_broadaddr;
        struct    sockaddr ifru_netmask;
        struct  sockaddr ifru_hwaddr;
        short    ifru_flags;
        int    ifru_ivalue;
        int    ifru_mtu;
        struct  ifmap ifru_map;
        char    ifru_slave[IFNAMSIZ];    /* Just fits the size */
        char    ifru_newname[IFNAMSIZ];
        void __user *    ifru_data;
        struct    if_settings ifru_settings;
    } ifr_ifru;
};
#define 	ifr_name    ifr_ifrn.ifrn_name    		/* interface name */
#define		ifr_hwaddr    ifr_ifru.ifru_hwaddr    	/* MAC address*/
#define    	ifr_addr    ifr_ifru.ifru_addr    		/* address */
#define    	ifr_dstaddr    ifr_ifru.ifru_dstaddr    /* other end of p-p lnk */
#define    	ifr_broadaddr    ifr_ifru.ifru_broadaddr    /* broadcast address */
#define    	ifr_netmask    ifr_ifru.ifru_netmask    /* interface net mask    */
#define    	ifr_flags    ifr_ifru.ifru_flags    	/* flags */
#define    	ifr_metric    ifr_ifru.ifru_ivalue    	/* metric */
#define    	ifr_mtu        ifr_ifru.ifru_mtu    	/* mtu */
#define 	ifr_map		ifr_ifru.ifru_map    		/* device map */
#define 	ifr_slave    ifr_ifru.ifru_slave   		/* slave device */
#define    	ifr_data    ifr_ifru.ifru_data    		/* for use by interface */
#define 	ifr_ifindex    ifr_ifru.ifru_ivalue		/* interface index */
#define 	ifr_bandwidth    ifr_ifru.ifru_ivalue   /* link bandwidth */
#define 	ifr_qlen    ifr_ifru.ifru_ivalue    	/* Queue length */
#define 	ifr_newname    ifr_ifru.ifru_newname    /* New name */
#define 	ifr_settings    ifr_ifru.ifru_settings  /* Device/proto settings*/

• 编程示例：

  #include <arpa/inet.h>
  #include <net/if.h>
  #include <net/if_arp.h>
  #include <netinet/in.h>
  #include <stdio.h>
  #include <sys/ioctl.h>
  #include <sys/socket.h>
  #include <unistd.h>
   
  #define MAXINTERFACES 16    /* 最大接口数 */
   
  int fd;         /* 套接字 */
  int if_len;     /* 接口数量 */
  struct ifreq buf[MAXINTERFACES];    /* ifreq结构数组 */
  struct ifconf ifc;                  /* ifconf结构 */
   
  int main(argc, argv)
  {
      /* 建立IPv4的UDP套接字fd */
      if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
      {
          perror("socket(AF_INET, SOCK_DGRAM, 0)");
          return -1;
      }
   
      /* 初始化ifconf结构 */
      ifc.ifc_len = sizeof(buf);
      ifc.ifc_buf = (caddr_t) buf;
   
      /* 获得接口列表 */
      if (ioctl(fd, SIOCGIFCONF, (char *) &ifc) == -1)
      {
          perror("SIOCGIFCONF ioctl");
          return -1;
      }
   
      if_len = ifc.ifc_len / sizeof(struct ifreq); /* 接口数量 */
      printf("接口数量:%d\n", if_len);
   
      while (if_len > 0) /* 遍历每个接口 */
      {
          printf("接口：%s/n", buf[if_len].ifr_name); /* 接口名称 */
   
          /* 获得接口标志 */
          if (!(ioctl(fd, SIOCGIFFLAGS, (char *) &buf[if_len])))
          {
              /* 接口状态 */
              if (buf[if_len].ifr_flags & IFF_UP)
              {
                  printf("接口状态: UP\n");
              }
              else
              {
                  printf("接口状态: DOWN\n");
              }
          }
          else
          {
              char str[256];
              sprintf(str, "SIOCGIFFLAGS ioctl %s", buf[if_len].ifr_name);
              perror(str);
          }
   
   
          /* IP地址 */
          if (!(ioctl(fd, SIOCGIFADDR, (char *) &buf[if_len])))
          {
              printf("IP地址:%s/n",\
                     (char*)inet_ntoa(((struct sockaddr_in*)(&buf[if_len].ifr_addr))->sin_addr));
          }
          else
          {
              char str[256];
              sprintf(str, "SIOCGIFADDR ioctl %s", buf[if_len].ifr_name);
              perror(str);
          }
   
          /* 子网掩码 */
          if (!(ioctl(fd, SIOCGIFNETMASK, (char *) &buf[if_len])))
          {
              printf("子网掩码:%s/n",
                      (char*)inet_ntoa(((struct sockaddr_in*)(&buf[if_len].ifr_addr))->sin_addr));
          }
          else
          {
              char str[256];
              sprintf(str, "SIOCGIFADDR ioctl %s", buf[if_len].ifr_name);
              perror(str);
          }
   
          /* 广播地址 */
          if (!(ioctl(fd, SIOCGIFBRDADDR, (char *) &buf[if_len])))
          {
              printf("广播地址:%s/n",
                      (char*)inet_ntoa(((struct sockaddr_in*) (&buf[if_len].ifr_addr))->sin_addr));
          }
          else
          {
              char str[256];
              sprintf(str, "SIOCGIFADDR ioctl %s", buf[if_len].ifr_name);
              perror(str);
          }
   
          /*MAC地址 */
          if (!(ioctl(fd, SIOCGIFHWADDR, (char *) &buf[if_len])))
          {
              printf("MAC地址:%02x:%02x:%02x:%02x:%02x:%02x/n/n",
                      (unsigned char) buf[if_len].ifr_hwaddr.sa_data[0],
                      (unsigned char) buf[if_len].ifr_hwaddr.sa_data[1],
                      (unsigned char) buf[if_len].ifr_hwaddr.sa_data[2],
                      (unsigned char) buf[if_len].ifr_hwaddr.sa_data[3],
                      (unsigned char) buf[if_len].ifr_hwaddr.sa_data[4],
                      (unsigned char) buf[if_len].ifr_hwaddr.sa_data[5]);
          }
          else
          {
              char str[256];
              sprintf(str, "SIOCGIFHWADDR ioctl %s", buf[if_len].ifr_name);
              perror(str);
          }
      }//while end
   
      //关闭socket
      close(fd);
      return 0;
  }
  

• 拓展链接

  • http://blog.csdn.net/jk110333/article/details/8832077
  • http://www.360doc.com/content/12/0314/15/5782959_194281431.shtml

6.3 socket

• \linux-2.6.32.63\include\linux\net.h

struct socket 
{    
    /*
    1. state：socket状态
    typedef enum 
    {
        SS_FREE = 0,            //该socket还未分配
        SS_UNCONNECTED,         //未连向任何socket
        SS_CONNECTING,          //正在连接过程中
        SS_CONNECTED,           //已连向一个socket
        SS_DISCONNECTING        //正在断开连接的过程中
    }socket_state; 
    */
    socket_state        state;

    kmemcheck_bitfield_begin(type);
    /*
    2. type：socket类型
    enum sock_type 
    {
        SOCK_STREAM    	= 1,    //stream (connection) socket
        SOCK_DGRAM    	= 2,    //datagram (conn.less) socket
        SOCK_RAW    	= 3,    //raw socket
        SOCK_RDM    	= 4,    //reliably-delivered message
        SOCK_SEQPACKET  = 5,	//sequential packet socket
        SOCK_DCCP    	= 6,    //Datagram Congestion Control Protocol socket
        SOCK_PACKET    	= 10,   //linux specific way of getting packets at the dev level.
    };
    */
    short            type;
    kmemcheck_bitfield_end(type);

    /*
    3. flags：socket标志
        1) #define SOCK_ASYNC_NOSPACE 	0
        2) #define SOCK_ASYNC_WAITDATA 	1
        3) #define SOCK_NOSPACE 		2
        4) #define SOCK_PASSCRED 		3
        5) #define SOCK_PASSSEC 		4
    */
    unsigned long        flags;

    //fasync_list is used when processes have chosen asynchronous handling of this 'file'
    struct fasync_struct    *fasync_list;
    //4. Not used by sockets in AF_INET
    wait_queue_head_t    wait;

    //5. file holds a reference to the primary file structure associated with this socket
    struct file        *file;

    //6. sk contains most of the useful state associated with a socket. 
    struct sock        *sk;

    //7. ops：定义了当前socket的处理函数
    const struct proto_ops    *ops;
};

6.4 sock

• struct sock本身不能获取到当前socket的IP、Port相关信息，要通过inet_sk()进行转换得到struct inet_sock才能得到IP、Port相关信息。但struct sock保存了当前socket大量的元描述信息。
• \linux-2.6.32.63\include\net\sock.h

struct sock 
{
    /*
     * Now struct inet_timewait_sock also uses sock_common, so please just
     * don't add nothing before this first member (__sk_common) --acme
     */
    //shared layout with inet_timewait_sock
    struct sock_common    __sk_common;
#define sk_node            __sk_common.skc_node
#define sk_nulls_node        __sk_common.skc_nulls_node
#define sk_refcnt        __sk_common.skc_refcnt

#define sk_copy_start        __sk_common.skc_hash
#define sk_hash            __sk_common.skc_hash
#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_bind_node        __sk_common.skc_bind_node
#define sk_prot            __sk_common.skc_prot
#define sk_net            __sk_common.skc_net

    kmemcheck_bitfield_begin(flags);
    //mask of %SEND_SHUTDOWN and/or %RCV_SHUTDOWN
    unsigned int sk_shutdown  : 2,
                //%SO_NO_CHECK setting, wether or not checkup packets
                sk_no_check  : 2,
                //%SO_SNDBUF and %SO_RCVBUF settings
                sk_userlocks : 4,
                //which protocol this socket belongs in this network family
                sk_protocol  : 8,
                //socket type (%SOCK_STREAM, etc)
                sk_type      : 16;
    kmemcheck_bitfield_end(flags);
    
    int            sk_rcvbuf;	//size of receive buffer in bytes  
    socket_lock_t        sk_lock;	//synchronizer
    /*
     * 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;
    
    wait_queue_head_t    *sk_sleep;	//sock wait queue
    
    struct dst_entry    *sk_dst_cache;	//destination cache

#ifdef CONFIG_XFRM
    struct xfrm_policy    *sk_policy[2];	//flow policy
#endif

    rwlock_t        sk_dst_lock;    	//destination cache lock
    atomic_t        sk_rmem_alloc;    	//receive queue bytes committed
    atomic_t        sk_wmem_alloc;		//transmit queue bytes committed
    atomic_t        sk_omem_alloc;		//"o" is "option" or "other"

    int            sk_sndbuf;    //size of send buffer in bytes

    struct sk_buff_head    sk_receive_queue;    //incoming packets
    struct sk_buff_head    sk_write_queue;    //Packet sending queue

#ifdef CONFIG_NET_DMA
    struct sk_buff_head    sk_async_wait_queue;    //DMA copied packets
#endif

    int            sk_wmem_queued;    //persistent queue size
    int            sk_forward_alloc;    //space allocated forward
    gfp_t            sk_allocation;    //allocation mode
    int            sk_route_caps;    //route capabilities (e.g. %NETIF_F_TSO)
    int            sk_gso_type;    //GSO type (e.g. %SKB_GSO_TCPV4)
    unsigned int        sk_gso_max_size;    //Maximum GSO segment size to build
    int            sk_rcvlowat;    //%SO_RCVLOWAT setting
    /*
    1. %SO_LINGER (l_onoff)
    2. %SO_BROADCAST
    3. %SO_KEEPALIVE
    4. %SO_OOBINLINE settings
    5. %SO_TIMESTAMPING settings
    */
    unsigned long         sk_flags;
    
    unsigned long            sk_lingertime;	//%SO_LINGER l_linger setting
    struct sk_buff_head    sk_error_queue;    //rarely used
    //sk_prot of original sock creator (see ipv6_setsockopt, IPV6_ADDRFORM for instance)
    struct proto        *sk_prot_creator;
    
    //used with the callbacks in the end of this struct
    rwlock_t        sk_callback_lock;
    //last error
    int            sk_err,
                //rrors that don't cause failure but are the cause of a persistent failure not just 'timed out'
                sk_err_soft;
                    //raw/udp drops counter
    atomic_t        sk_drops;
    //always used with the per-socket spinlock held
    //current listen backlog
    unsigned short        sk_ack_backlog;
    //listen backlog set in listen()
    unsigned short        sk_max_ack_backlog;
    //%SO_PRIORITY setting
    __u32            sk_priority;
    //%SO_PEERCRED setting
    struct ucred        sk_peercred;
    //%SO_RCVTIMEO setting
    long            sk_rcvtimeo;
    //%SO_SNDTIMEO setting
    long            sk_sndtimeo;
    //socket filtering instructions
    struct sk_filter          *sk_filter;
    //private area, net family specific, when not using slab
    void            *sk_protinfo;
    //sock cleanup timer
    struct timer_list    sk_timer;
    //time stamp of last packet received
    ktime_t            sk_stamp;
    //Identd and reporting IO signals
    struct socket        *sk_socket;
    //RPC layer private data
    void            *sk_user_data;
    //cached page for sendmsg
    struct page        *sk_sndmsg_page;
    //front of stuff to transmit
    struct sk_buff        *sk_send_head;
    //cached offset for sendmsg
    __u32            sk_sndmsg_off;
    //a write to stream socket waits to start
    int            sk_write_pending;
#ifdef CONFIG_SECURITY
    //used by security modules
    void            *sk_security;
#endif
    //generic packet mark
    __u32            sk_mark;
    /* XXX 4 bytes hole on 64 bit */
    //callback to indicate change in the state of the sock
    void            (*sk_state_change)(struct sock *sk);
    //callback to indicate there is data to be processed
    void            (*sk_data_ready)(struct sock *sk, int bytes);
    //callback to indicate there is bf sending space available
    void            (*sk_write_space)(struct sock *sk);
    //callback to indicate errors (e.g. %MSG_ERRQUEUE)
    void            (*sk_error_report)(struct sock *sk);
    //callback to process the backlog
      int            (*sk_backlog_rcv)(struct sock *sk, struct sk_buff *skb);  
      //called at sock freeing time, i.e. when all refcnt == 0
    void                    (*sk_destruct)(struct sock *sk);
}

6.5 proto_ops

• \linux-2.6.32.63\include\linux\net.h

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 (*compat_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, unsigned int optlen);
    
    int (*getsockopt)(struct socket *sock, int level, \
                      int optname, char __user *optval, int __user *optlen);
    
    int (*compat_setsockopt)(struct socket *sock, int level,\
                             int optname, char __user *optval, unsigned int optlen);
    
    int (*compat_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);
    
    /* Notes for implementing recvmsg:
     * ===============================
     * msg->msg_namelen should get updated by the recvmsg handlers
     * iff msg_name != NULL. It is by default 0 to prevent
     * returning uninitialized memory to user space.  The recvfrom
     * handlers can assume that msg.msg_name is either NULL or has
     * a minimum size of sizeof(struct sockaddr_storage).
     */
    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);
    
    ssize_t (*splice_read)(struct socket *sock,\
                           loff_t *ppos, struct pipe_inode_info *pipe, \
                           size_t len, unsigned int flags);
};

6.6 inet_sock

• 在实际编程中，我们需要使用inet_sk()，将"struct sock"结果强制转换为"struct inet_sock"之后，才可以从中取出我们想要的IP、Port等信息

• \linux-2.6.32.63\include\net\inet_sock.h

  static inline struct inet_sock *inet_sk(const struct sock *sk)
  {
      return (struct inet_sock *)sk;
  }
  

• inet_sock的结构体定义如下

  struct inet_sock 
  {
      /* sk and pinet6 has to be the first two members of inet_sock */
      struct sock        sk;    //ancestor class
  #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
      struct ipv6_pinfo    *pinet6;    //pointer to IPv6 control block
  #endif
      
      /* Socket demultiplex comparisons on incoming packets. */
      //Foreign IPv4 addr
      __be32            daddr;
      //Bound local IPv4 addr
      __be32            rcv_saddr;
      //Destination port
      __be16            dport;
      //Local port
      __u16            num;
      //Sending source
      __be32            saddr;
      //Unicast TTL
      __s16            uc_ttl;
      __u16            cmsg_flags;
      struct ip_options_rcu    *inet_opt;
      //Source port
      __be16            sport;
      //ID counter for DF pkts
      __u16            id;
      //TOS
      __u8            tos;
      //Multicasting TTL
      __u8	mc_ttl;
      __u8    pmtudisc;
      __u8    recverr:1,
              //is this an inet_connection_sock?
              is_icsk:1,
              freebind:1,
              hdrincl:1,
              mc_loop:1,
              transparent:1,
              mc_all:1;
  
      int            mc_index;          //Multicast device index
      __be32            mc_addr;
      struct ip_mc_socklist    *mc_list;
      //info to build ip hdr on each ip frag while socket is corked
      struct 
      {
          unsigned int        flags;
          unsigned int        fragsize;
          struct ip_options    *opt;
          struct dst_entry    *dst;
          int            length; /* Total length of all frames */
          __be32            addr;
          struct flowi        fl;
      } cork;
  };
  

6.7 sockaddr

struct sockaddr 
{
    unsigned short    sa_family;    // address family, AF_xxx
    char	sa_data[14];      // 14 bytes of protocol address
};

/* Structure describing an Internet (IP) socket address. */
#define __SOCK_SIZE__    16        /* sizeof(struct sockaddr)    */

struct sockaddr_in 
{

    sa_family_t	sin_family;        /* Address family */
    __be16	sin_port;    /* Port number */
    struct in_addr    sin_addr;        /* Internet address */

    /* Pad to size of `struct sockaddr'. */
    unsigned char	__pad[__SOCK_SIZE__ - sizeof(short int) - sizeof(unsigned short int) - sizeof(struct in_addr)];
};

#define sin_zero    __pad        /* for BSD UNIX comp. -FvK    */

/* Internet address. */
struct in_addr 
{
    __be32    s_addr;
};