LINUX下getsockopt和setsockopt函数

这两个函数仅用于套接字。

函数原型：

 #include <sys/socket.h>
 #include <sys/types.h>

 int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen);

 int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen);

sockfd:必须指向一个打开的套接字描述符

level:指定系统中解释选项的代码或为通用套接字代码，或为某个特定于协议的代码（例如IPv4、IPv6、TCP或SCTP）。

optval:指向某个变量（＊optval）的指针，setsockopt从*optval中取得选项设置的新值，getsockopt则把以获取的选项当前值存入*optval。

optlen:指定*optval的大小

套接字选项的汇总可以查看unix网络编程（卷1）151页 图7-1和图7-2.

并非所有实现都支持所有的套接字选项，下面的程序可以简单测试系统是否支持选项：

 /* include checkopts1 */
 /* *INDENT-OFF* */
 #include    "unp.h"
 #include    <netinet/tcp.h>        /* for TCP_xxx defines */

 union val {
   int                i_val;
   long                l_val;
   struct linger        linger_val;
   struct timeval    timeval_val;
 } val;

 static char    *sock_str_flag(union val *, int);
 static char    *sock_str_int(union val *, int);
 static char    *sock_str_linger(union val *, int);
 static char    *sock_str_timeval(union val *, int);

 struct sock_opts {
   const char       *opt_str;
   int        opt_level;
   int        opt_name;
   char   *(*opt_val_str)(union val *, int);
 } sock_opts[] = {
 #ifdef  SO_BROADCAST
     { "SO_BROADCAST",        SOL_SOCKET,    SO_BROADCAST,    sock_str_flag },
 #else
     { "SO_BROADCAST",            ,        ,        NULL},
 #endif
 #ifdef  SO_DEBUG
     { "SO_DEBUG",            SOL_SOCKET,    SO_DEBUG,        sock_str_flag },
 #else
     { "SO_DEBUG",                ,        ,        NULL},
 #endif
 #ifdef  SO_DONTROUTE
     { "SO_DONTROUTE",        SOL_SOCKET,    SO_DONTROUTE,    sock_str_flag },
 #else
     { "SO_DONTROUTE",            ,        ,        NULL},
 #endif
 #ifdef  SO_ERROR
     { "SO_ERROR",            SOL_SOCKET,    SO_ERROR,        sock_str_int },
 #else
     { "SO_ERROR",                ,        ,        NULL},
 #endif
 #ifdef  SO_KEEPALIVE
     { "SO_KEEPALIVE",        SOL_SOCKET,    SO_KEEPALIVE,    sock_str_flag },
 #else
     { "SO_KEEPALIVE",            ,        ,        NULL},
 #endif
 #ifdef  SO_LINGER
     { "SO_LINGER",            SOL_SOCKET,    SO_LINGER,        sock_str_linger },
 #else
     { "SO_LINGER",                ,        ,        NULL},
 #endif
 #ifdef  SO_OOBINLINE
     { "SO_OOBINLINE",        SOL_SOCKET,    SO_OOBINLINE,    sock_str_flag },
 #else
     : "SO_OOBINLINE",            ,        ,        NULL},
 #endif
 #ifdef  SO_RCVBUF
     { "SO_RCVBUF",            SOL_SOCKET,    SO_RCVBUF,        sock_str_int },
 #else
     { "SO_RCVBUF",                ,        ,        NULL},
 #endif
 #ifdef  SO_SNDBUF
     { "SO_SNDBUF",            SOL_SOCKET,    SO_SNDBUF,        sock_str_int },
 #else
     { "SO_SNDBUF",                ,        ,        NULL},
 #endif
 #ifdef  SO_RCVLOWAT
     { "SO_RCVLOWAT",        SOL_SOCKET,    SO_RCVLOWAT,    sock_str_int },
 #else
     { "SO_RCVLOWAT",            ,        ,        NULL},
 #endif
 #ifdef  SO_SNDLOWAT
     { "SO_SNDLOWAT",        SOL_SOCKET,    SO_SNDLOWAT,    sock_str_int },
 #else
     { "SO_SNDLOWAT",            ,        ,        NULL},
 #endif
 #ifdef  SO_RCVTIMEO
     { "SO_RCVTIMEO",        SOL_SOCKET,    SO_RCVTIMEO,    sock_str_timeval },
 #else
     { "SO_RCVTIMEO",            ,        ,        NULL},
 #endif
 #ifdef  SO_SNDTIMEO
     { "SO_SNDTIMEO",        SOL_SOCKET,    SO_SNDTIMEO,    sock_str_timeval },
 #else
     { "SO_SNDTIMEO",            ,        ,        NULL},
 #endif
 #ifdef  SO_REUSEADDR
     { "SO_REUSEADDR",        SOL_SOCKET,    SO_REUSEADDR,    sock_str_flag },
 #else
     { "SO_REUSEADDR",            ,        ,        NULL},
 #endif
 #ifdef    SO_REUSEPORT
     { "SO_REUSEPORT",        SOL_SOCKET,    SO_REUSEPORT,    sock_str_flag },
 #else
     { "SO_REUSEPORT",        ,            ,                NULL },
 #endif
 #ifdef  SO_TYPE
     { "SO_TYPE",            SOL_SOCKET,    SO_TYPE,        sock_str_int },
 #else
     { "SO_TYPE",            ,            ,        NULL},
 #endif
 #ifdef  SO_USELOOPBACK
     { "SO_USELOOPBACK",        SOL_SOCKET,    SO_USELOOPBACK,    sock_str_flag },
 #else
     { "SO_USELOOPBACK",        ,            ,                NULL},
 #endif
 #ifdef  IP_TOS
     { "IP_TOS",                IPPROTO_IP,    IP_TOS,            sock_str_int },
 #else
     { "IP_TOS",            ,            ,        NULL},
 #endif
 #ifdef  IP_TTL
     { "IP_TTL",                IPPROTO_IP,    IP_TTL,            sock_str_int },
 #else
     { "IP_TTL",            ,            ,        NULL},
 #endif
 #ifdef    IPV6_DONTFRAG
     { "IPV6_DONTFRAG",        IPPROTO_IPV6,IPV6_DONTFRAG,    sock_str_flag },
 #else
     { "IPV6_DONTFRAG",        ,            ,                NULL },
 #endif
 #ifdef    IPV6_UNICAST_HOPS
     { "IPV6_UNICAST_HOPS",    IPPROTO_IPV6,IPV6_UNICAST_HOPS,sock_str_int },
 #else
     { "IPV6_UNICAST_HOPS",    ,            ,                NULL },
 #endif
 #ifdef    IPV6_V6ONLY
     { "IPV6_V6ONLY",        IPPROTO_IPV6,IPV6_V6ONLY,    sock_str_flag },
 #else
     { "IPV6_V6ONLY",        ,            ,                NULL },
 #endif
 #ifdef  TCP_MAXSEG
     { "TCP_MAXSEG",            IPPROTO_TCP,TCP_MAXSEG,        sock_str_int },
 #else
     { "TCP_MAXSEG",            ,            ,            NULL},
 #endif
 #ifdef  TCP_NODELAY
     { "TCP_NODELAY",        IPPROTO_TCP,TCP_NODELAY,    sock_str_flag },
 #else
     { "TCP_NODELAY",        ,            ,            NULL},
 #endif
 #ifdef    SCTP_AUTOCLOSE
     { "SCTP_AUTOCLOSE",        IPPROTO_SCTP,SCTP_AUTOCLOSE,sock_str_int },
 #else
     { "SCTP_AUTOCLOSE",        ,            ,                NULL },
 #endif
 #ifdef    SCTP_MAXBURST
     { "SCTP_MAXBURST",        IPPROTO_SCTP,SCTP_MAXBURST,    sock_str_int },
 #else
     { "SCTP_MAXBURST",        ,            ,                NULL },
 #endif
 #ifdef    SCTP_MAXSEG
     { "SCTP_MAXSEG",        IPPROTO_SCTP,SCTP_MAXSEG,    sock_str_int },
 #else
     { "SCTP_MAXSEG",        ,            ,                NULL },
 #endif
 #ifdef    SCTP_NODELAY
     { "SCTP_NODELAY",        IPPROTO_SCTP,SCTP_NODELAY,    sock_str_flag },
 #else
     { "SCTP_NODELAY",        ,            ,                NULL },
 #endif
     { NULL,                    ,            ,                NULL }
 };
 /* *INDENT-ON* */
 /* end checkopts1 */

 /* include checkopts2 */
 int
 main(int argc, char **argv)
 {
     int                    fd;
     socklen_t            len;
     struct sock_opts    *ptr;

     for (ptr = sock_opts; ptr->opt_str != NULL; ptr++) {
         printf("%s: ", ptr->opt_str);
         if (ptr->opt_val_str == NULL)
             printf("(undefined)\n");
         else {
             switch(ptr->opt_level) {
             case SOL_SOCKET:
             case IPPROTO_IP:
             case IPPROTO_TCP:
                 fd = Socket(AF_INET, SOCK_STREAM, );
                 break;
 #ifdef    IPV6
             case IPPROTO_IPV6:
                 fd = Socket(AF_INET6, SOCK_STREAM, );
                 break;
 #endif
 #ifdef    IPPROTO_SCTP
             case IPPROTO_SCTP:
                 fd = Socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
                 break;
 #endif
             default:
                 err_quit("Can't create fd for level %d\n", ptr->opt_level);
             }

             len = sizeof(val);
             if (getsockopt(fd, ptr->opt_level, ptr->opt_name,
                            &val, &len) == -) {
                 err_ret("getsockopt error");
             } else {
                 printf("default = %s\n", (*ptr->opt_val_str)(&val, len));
             }
             close(fd);
         }
     }
     exit();
 }
 /* end checkopts2 */

 /* include checkopts3 */
 static char    strres[];

 static char    *
 sock_str_flag(union val *ptr, int len)
 {
 /* *INDENT-OFF* */
     if (len != sizeof(int))
         snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
     else
         snprintf(strres, sizeof(strres),
                  "%s", (ptr->i_val == ) ? "off" : "on");
     return(strres);
 /* *INDENT-ON* */
 }
 /* end checkopts3 */

 static char    *
 sock_str_int(union val *ptr, int len)
 {
     if (len != sizeof(int))
         snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
     else
         snprintf(strres, sizeof(strres), "%d", ptr->i_val);
     return(strres);
 }

 static char    *
 sock_str_linger(union val *ptr, int len)
 {
     struct linger    *lptr = &ptr->linger_val;

     if (len != sizeof(struct linger))
         snprintf(strres, sizeof(strres),
                  "size (%d) not sizeof(struct linger)", len);
     else
         snprintf(strres, sizeof(strres), "l_onoff = %d, l_linger = %d",
                  lptr->l_onoff, lptr->l_linger);
     return(strres);
 }

 static char    *
 sock_str_timeval(union val *ptr, int len)
 {
     struct timeval    *tvptr = &ptr->timeval_val;

     if (len != sizeof(struct timeval))
         snprintf(strres, sizeof(strres),
                  "size (%d) not sizeof(struct timeval)", len);
     else
         snprintf(strres, sizeof(strres), "%ld sec, %ld usec",
                  tvptr->tv_sec, tvptr->tv_usec);
     return(strres);
 }

我用的系统是Ubuntu 13.04，结果截图：