NAME
getsockopt, setsockopt - get and set options on sockets
获取或者设置套接字的选项
SYNOPSIS
#include <sys/types.h> /* See NOTES */
#include <sys/socket.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);sock：将要被设置或者获取选项的套接字。
level：选项所在的协议层。
optname：需要访问的选项名。
optval：对于getsockopt()，指向返回选项值的缓冲。
对于setsockopt()，指向包含新选项值的缓冲。
optlen：对于getsockopt()，作为入口参数时，选项值的最大长度。作为出口参数时，选项值的实际长度。
对于setsockopt()，The size, in bytes, of the optval buffer.
level指定控制套接字的层次.可以取三种值:
1)SOL_SOCKET:通用套接字选项.
2)IPPROTO_IP:IP选项.
3)IPPROTO_TCP:TCP选项.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EBADF The argument sockfd is not a valid descriptor.
EFAULT The address pointed to by optval is not in a valid part of the process address space. For getsockopt(), this error may
also be returned if optlen is not in a valid part of the process address space.//
EINVAL optlen invalid in setsockopt(). In some cases this error can also occur for an invalid value in optval (e.g., for the
IP_ADD_MEMBERSHIP option described in ip(7)).
ENOPROTOOPT
The option is unknown at the level indicated.
ENOTSOCK The argument sockfd is a file, not a socket.
EBADF：sock不是有效的文件描述词
EFAULT：optval指向的内存并非有效的进程空间
EINVAL：在调用setsockopt()时，optlen无效
ENOPROTOOPT：指定的协议层不能识别选项
ENOTSOCK：sock描述的不是套接字
套接字选项和IP层的套接字选项汇总见《unix网络编程第三版卷一》P151图7-1
下面用一段小代码来检查选项是否受支持并获取默认值：
root@wl-Lenovo-B590:/myworkspace/unixnetwork/unpv13e/sockopt# cat -n checkopts.c
1 /* include checkopts1 */
2 /* *INDENT-OFF* */
3 #include "unp.h"
4 #include <netinet/tcp.h> /* for TCP_xxx defines */
5
6 union val {
7 int i_val;
8 long l_val;
9 struct linger linger_val;
10 struct timeval timeval_val;
11 } val;
12
13 static char *sock_str_flag(union val *, int);
14 static char *sock_str_int(union val *, int);
15 static char *sock_str_linger(union val *, int);
16 static char *sock_str_timeval(union val *, int);
17
18 struct sock_opts {
19 const char *opt_str;
20 int opt_level;
21 int opt_name;
22 char *(*opt_val_str)(union val *, int);
23 } sock_opts[] = {
24 { "SO_BROADCAST", SOL_SOCKET, SO_BROADCAST, sock_str_flag },
25 { "SO_DEBUG", SOL_SOCKET, SO_DEBUG, sock_str_flag },
26 { "SO_DONTROUTE", SOL_SOCKET, SO_DONTROUTE, sock_str_flag },
27 { "SO_ERROR", SOL_SOCKET, SO_ERROR, sock_str_int },
28 { "SO_KEEPALIVE", SOL_SOCKET, SO_KEEPALIVE, sock_str_flag },
29 { "SO_LINGER", SOL_SOCKET, SO_LINGER, sock_str_linger },
30 { "SO_OOBINLINE", SOL_SOCKET, SO_OOBINLINE, sock_str_flag },
31 { "SO_RCVBUF", SOL_SOCKET, SO_RCVBUF, sock_str_int },
32 { "SO_SNDBUF", SOL_SOCKET, SO_SNDBUF, sock_str_int },
33 { "SO_RCVLOWAT", SOL_SOCKET, SO_RCVLOWAT, sock_str_int },
34 { "SO_SNDLOWAT", SOL_SOCKET, SO_SNDLOWAT, sock_str_int },
35 { "SO_RCVTIMEO", SOL_SOCKET, SO_RCVTIMEO, sock_str_timeval },
36 { "SO_SNDTIMEO", SOL_SOCKET, SO_SNDTIMEO, sock_str_timeval },
37 { "SO_REUSEADDR", SOL_SOCKET, SO_REUSEADDR, sock_str_flag },
38 #ifdef SO_REUSEPORT
39 { "SO_REUSEPORT", SOL_SOCKET, SO_REUSEPORT, sock_str_flag },
40 #else
41 { "SO_REUSEPORT", 0, 0, NULL },
42 #endif
43 { "SO_TYPE", SOL_SOCKET, SO_TYPE, sock_str_int },
44 // { "SO_USELOOPBACK", SOL_SOCKET, SO_USELOOPBACK, sock_str_flag },
45 { "IP_TOS", IPPROTO_IP, IP_TOS, sock_str_int },
46 { "IP_TTL", IPPROTO_IP, IP_TTL, sock_str_int },
47 #ifdef IPV6_DONTFRAG
48 { "IPV6_DONTFRAG", IPPROTO_IPV6,IPV6_DONTFRAG, sock_str_flag },
49 #else
50 { "IPV6_DONTFRAG", 0, 0, NULL },
51 #endif
52 #ifdef IPV6_UNICAST_HOPS
53 { "IPV6_UNICAST_HOPS", IPPROTO_IPV6,IPV6_UNICAST_HOPS,sock_str_int },
54 #else
55 { "IPV6_UNICAST_HOPS", 0, 0, NULL },
56 #endif
57 #ifdef IPV6_V6ONLY
58 { "IPV6_V6ONLY", IPPROTO_IPV6,IPV6_V6ONLY, sock_str_flag },
59 #else
60 { "IPV6_V6ONLY", 0, 0, NULL },
61 #endif
62 { "TCP_MAXSEG", IPPROTO_TCP,TCP_MAXSEG, sock_str_int },
63 { "TCP_NODELAY", IPPROTO_TCP,TCP_NODELAY, sock_str_flag },
64 #ifdef SCTP_AUTOCLOSE
65 { "SCTP_AUTOCLOSE", IPPROTO_SCTP,SCTP_AUTOCLOSE,sock_str_int },
66 #else
67 { "SCTP_AUTOCLOSE", 0, 0, NULL },
68 #endif
69 #ifdef SCTP_MAXBURST
70 { "SCTP_MAXBURST", IPPROTO_SCTP,SCTP_MAXBURST, sock_str_int },
71 #else
72 { "SCTP_MAXBURST", 0, 0, NULL },
73 #endif
74 #ifdef SCTP_MAXSEG
75 { "SCTP_MAXSEG", IPPROTO_SCTP,SCTP_MAXSEG, sock_str_int },
76 #else
77 { "SCTP_MAXSEG", 0, 0, NULL },
78 #endif
79 #ifdef SCTP_NODELAY
80 { "SCTP_NODELAY", IPPROTO_SCTP,SCTP_NODELAY, sock_str_flag },
81 #else
82 { "SCTP_NODELAY", 0, 0, NULL },
83 #endif
84 { NULL, 0, 0, NULL }
85 };
86 /* *INDENT-ON* */
87 /* end checkopts1 */
88
89 /* include checkopts2 */
90 int
91 main(int argc, char **argv)
92 {
93 int fd;
94 socklen_t len;
95 struct sock_opts *ptr;
96
97 for (ptr = sock_opts; ptr->opt_str != NULL; ptr++) {
98 printf("%s: ", ptr->opt_str);
99 if (ptr->opt_val_str == NULL)
100 printf("(undefined)\n");
101 else {
102 switch(ptr->opt_level) {
103 case SOL_SOCKET:
104 case IPPROTO_IP:
105 case IPPROTO_TCP:
106 fd = Socket(AF_INET, SOCK_STREAM, 0);
107 break;
108 #ifdef IPV6
109 case IPPROTO_IPV6:
110 fd = Socket(AF_INET6, SOCK_STREAM, 0);
111 break;
112 #endif
113 #ifdef IPPROTO_SCTP
114 case IPPROTO_SCTP:
115 fd = Socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
116 break;
117 #endif
118 default:
119 err_quit("Can‘t create fd for level %d\n", ptr->opt_level);
120 }
121
122 len = sizeof(val);
123 if (getsockopt(fd, ptr->opt_level, ptr->opt_name,
124 &val, &len) == -1) {
125 err_ret("getsockopt error");
126 } else {
127 printf("default = %s\n", (*ptr->opt_val_str)(&val, len));
128 }
129 close(fd);
130 }
131 }
132 exit(0);
133 }
134 /* end checkopts2 */
135
136 /* include checkopts3 */
137 static char strres[128];
138
139 static char *
140 sock_str_flag(union val *ptr, int len)
141 {
142 /* *INDENT-OFF* */
143 if (len != sizeof(int))
144 snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
145 else
146 snprintf(strres, sizeof(strres),
147 "%s", (ptr->i_val == 0) ? "off" : "on");
148 return(strres);
149 /* *INDENT-ON* */
150 }
151 /* end checkopts3 */
152
153 static char *
154 sock_str_int(union val *ptr, int len)
155 {
156 if (len != sizeof(int))
157 snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
158 else
159 snprintf(strres, sizeof(strres), "%d", ptr->i_val);
160 return(strres);
161 }
162
163 static char *
164 sock_str_linger(union val *ptr, int len)
165 {
166 struct linger *lptr = &ptr->linger_val;
167
168 if (len != sizeof(struct linger))
169 snprintf(strres, sizeof(strres),
170 "size (%d) not sizeof(struct linger)", len);
171 else
172 snprintf(strres, sizeof(strres), "l_onoff = %d, l_linger = %d",
173 lptr->l_onoff, lptr->l_linger);
174 return(strres);
175 }
176
177 static char *
178 sock_str_timeval(union val *ptr, int len)
179 {
180 struct timeval *tvptr = &ptr->timeval_val;
181
182 if (len != sizeof(struct timeval))
183 snprintf(strres, sizeof(strres),
184 "size (%d) not sizeof(struct timeval)", len);
185 else
186 snprintf(strres, sizeof(strres), "%d sec, %d usec",
187 tvptr->tv_sec, tvptr->tv_usec);
188 return(strres);
189 }
root@wl-Lenovo-B590:/myworkspace/unixnetwork/unpv13e/sockopt# man getsockopt
参考：UNIX网络编程卷一
Linux Programmer‘s Manual
linux下getsockopt和setsockopt详解及测试,布布扣,bubuko.com
linux下getsockopt和setsockopt详解及测试
原文：http://blog.csdn.net/hongkangwl/article/details/24105833
