用户态与内核态交互通信的方法不止一种，sockopt是比较方便的一个，写法也简单.
缺点就是使用 copy_from_user()/copy_to_user()完成内核和用户的通信， 效率其实不高， 多用在传递控制 选项 信息，不适合做大量的数据传输
用户态函数：
发送：int setsockopt ( int sockfd, int proto, int cmd, void *data, int datelen);
接收：int getsockopt(int sockfd, int proto, int cmd, void *data, int datalen)
第一个参数是socket描述符；
第二个参数proto是sock协议，IP RAW的就用SOL_SOCKET/SOL_IP等，TCP/UDP socket的可用SOL_SOCKET/SOL_IP/SOL_TCP/SOL_UDP等，即高层的socket是都可以使用低层socket的命令字 的，IPPROTO_IP；
第三个参数cmd是操作命令字，由自己定义；
第四个参数是数据缓冲区起始位置指针，set操作时是将缓冲区数据写入内核，get的时候是将内核中的数 据读入该缓冲区；
第五个参数数据长度
内核态函数
注册：nf_register_sockopt(struct nf_sockopt_ops *sockops)
解除：nf_unregister_sockopt(struct nf_sockopt_ops *sockops)
结构体 nf_sockopt_ops test_sockops
struct nf_sockopt_ops { struct list_head list; u_int8_t pf; // 协议族 /* Non-inclusive ranges: use 0/0/NULL to never get called. */ int set_optmin;// 定义最小set命令字 int set_optmax;// 定义最大set命令字 int (*set)(struct sock *sk, int optval, void __user *user, unsigned int len);// 定义set处理函数 #ifdef CONFIG_COMPAT int (*compat_set)(struct sock *sk, int optval, void __user *user, unsigned int len); #endif int get_optmin;// 定义最小get命令字 int get_optmax;// 定义最大get命令字 int (*get)(struct sock *sk, int optval, void __user *user, int *len);// 定义get处理函数 #ifdef CONFIG_COMPAT int (*compat_get)(struct sock *sk, int optval, void __user *user, int *len); #endif /* Use the module struct to lock set/get code in place */ struct module *owner; };
其中命令字不能和内核已有的重复，宜大不宜小。命令字很重要，是用来做标识符的。而且用户态和内核态要定义的相同，
系统调用如下：sockt==》sock_common_setsockopt==》sk->sk_prot->setsockopt==》ip_setsockopt（tcp为例）
==>do_ip_setsockopt
==> nf_setsockopt==>nf_sockopt
int ip_setsockopt(struct sock *sk, int level, int optname, char __user *optval, unsigned int optlen) { int err; if (level != SOL_IP) return -ENOPROTOOPT; err = do_ip_setsockopt(sk, level, optname, optval, optlen); #ifdef CONFIG_NETFILTER /* we need to exclude all possible ENOPROTOOPTs except default case */ if (err == -ENOPROTOOPT && optname != IP_HDRINCL && optname != IP_IPSEC_POLICY && optname != IP_XFRM_POLICY && !ip_mroute_opt(optname)) { lock_sock(sk); err = nf_setsockopt(sk, PF_INET, optname, optval, optlen); release_sock(sk); } #endif return err; } /* Call get/setsockopt() */ static int nf_sockopt(struct sock *sk, u_int8_t pf, int val, char __user *opt, int *len, int get) { struct nf_sockopt_ops *ops; int ret; ops = nf_sockopt_find(sk, pf, val, get); if (IS_ERR(ops)) return PTR_ERR(ops); if (get) ret = ops->get(sk, val, opt, len); else ret = ops->set(sk, val, opt, *len); module_put(ops->owner); return ret; } int nf_setsockopt(struct sock *sk, u_int8_t pf, int val, char __user *opt, unsigned int len) { return nf_sockopt(sk, pf, val, opt, &len, 0); }
#include <linux/module.h> #include <linux/kernel.h> #include <linux/types.h> #include <linux/string.h> #include <linux/netfilter_ipv4.h> #include <linux/init.h> #include <asm/uaccess.h> #define SOCKET_OPS_BASE 128 #define SOCKET_OPS_SET (SOCKET_OPS_BASE) #define SOCKET_OPS_GET (SOCKET_OPS_BASE) #define SOCKET_OPS_MAX (SOCKET_OPS_BASE + 1) #define KMSG "--------kernel---------" #define KMSG_LEN sizeof("--------kernel---------") MODULE_LICENSE("GPL"); MODULE_AUTHOR("SiasJack");/*作者*/ MODULE_DESCRIPTION("sockopt module,simple module");//描述 MODULE_VERSION("1.0");//版本号 static int recv_msg(struct sock *sk, int cmd, void __user *user, unsigned int len) { int ret = 0; printk(KERN_INFO "sockopt: recv_msg() "); if (cmd == SOCKET_OPS_SET) { char umsg[64]; int len = sizeof(char)*64; memset(umsg, 0, len); ret = copy_from_user(umsg, user, len); printk("recv_msg: umsg = %s. ret = %d ", umsg, ret); } return 0; } static int send_msg(struct sock *sk, int cmd, void __user *user, int *len) { int ret = 0; printk(KERN_INFO "sockopt: send_msg() "); if (cmd == SOCKET_OPS_GET) { ret = copy_to_user(user, KMSG, KMSG_LEN); printk("send_msg: umsg = %s. ret = %d. success ", KMSG, ret); } return 0; } static struct nf_sockopt_ops test_sockops = { .pf = PF_INET, .set_optmin = SOCKET_OPS_SET, .set_optmax = SOCKET_OPS_MAX, .set = recv_msg, .get_optmin = SOCKET_OPS_GET, .get_optmax = SOCKET_OPS_MAX, .get = send_msg, .owner = THIS_MODULE, }; static int __init init_sockopt(void) { printk(KERN_INFO "sockopt: init_sockopt() "); return nf_register_sockopt(&test_sockops); } static void __exit exit_sockopt(void) { printk(KERN_INFO "sockopt: fini_sockopt() "); nf_unregister_sockopt(&test_sockops); } module_init(init_sockopt);
#include <unistd.h> #include <stdio.h> #include <sys/socket.h> #include <linux/in.h> #include <string.h> #include <errno.h> #define SOCKET_OPS_BASE 128 #define SOCKET_OPS_SET (SOCKET_OPS_BASE) #define SOCKET_OPS_GET (SOCKET_OPS_BASE) #define SOCKET_OPS_MAX (SOCKET_OPS_BASE + 1) #define UMSG "----------user------------" #define UMSG_LEN sizeof("----------user------------") char kmsg[64]; int main(void) { int sockfd; int len; int ret; sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW); if(sockfd < 0) { printf("can not create a socket "); return -1; } /*call function recv_msg()*/ ret = setsockopt(sockfd, IPPROTO_IP, SOCKET_OPS_SET, UMSG, UMSG_LEN); printf("setsockopt: ret = %d. msg = %s ", ret, UMSG); len = sizeof(char)*64; /*call function send_msg()*/ ret = getsockopt(sockfd, IPPROTO_IP, SOCKET_OPS_GET, kmsg, &len); printf("getsockopt: ret = %d. msg = %s ", ret, kmsg); if (ret != 0) { printf("getsockopt error: errno = %d, errstr = %s ", errno, strerror(errno)); } close(sockfd); return 0; }