linux学习 内核提供 copy_from_user()/copy_to_user() 函数来实现内核态与用户态数据的拷贝,但这两个函数会引发阻塞,所以不能用在硬、软中断中。一般将这两个特殊拷贝函数用在类似于系统调用一类的函数中
在下面的代码中,内核模块注册了一组设置套接字选项的函数使得用户空间进程可以调用此组函数对内核态数据进行读写。
下面是有关操作步骤及源代码:
头文件:imp1.h
-
- #ifndef __IMP1_H__
- #define __IMP1_H__
-
- #define IMP1_OPS_BASIC 128
- #define IMP1_SET IMP1_OPS_BASIC
- #define IMP1_GET IMP1_OPS_BASIC
- #define IMP1_MAX IMP1_OPS_BASIC+1
-
- #endif
module:
编译:gcc -c -D__KERNEL__ -DMODULE imp1_k.c
查看module输出:方法一:dmesg, 方法二:tail -f /var/log/messages
/*imp1_k.c*/
- #ifndef __KERNEL__
- #define __KERNEL__
- #endif
-
- #ifndef MODULE
- #define MODULE
- #endif
-
- #include <linux/module.h>
- #include <linux/kernel.h>
- #include <linux/types.h>
- #include <linux/string.h>
- #include <linux/netfilter_ipv4.h>
- #include <linux/netfilter.h>
- #include <linux/init.h>
- #include <asm/uaccess.h>
- #include "imp1.h"
-
- #define KMSG "a message from kernel/n"
- #define KMSG_LEN sizeof("a message from kernel/n")
-
- static int data_to_kernel(struct sock *sk, int cmd, void *user,
- unsigned int len)
- {
- switch(cmd)
- {
- case IMP1_SET:
- {
- char umsg[64];
- memset(umsg, 0, sizeof(char)*64);
- copy_from_user(umsg, user, sizeof(char)*64);
- printk("umsg: %s", umsg);
- }
- break;
- }
- return 0;
- }
-
- static int data_from_kernel(struct sock *sk, int cmd, void *user, int *len)
- {
- switch(cmd)
- {
- case IMP1_GET:
- {
- copy_to_user(user, KMSG, KMSG_LEN);
- }
- break;
- }
- return 0;
- }
-
- static struct nf_sockopt_ops imp1_sockops =
- {
- .pf = PF_INET,
- .set_optmin = IMP1_SET,
- .set_optmax = IMP1_MAX,
- .set = data_to_kernel,
- .get_optmin = IMP1_GET,
- .get_optmax = IMP1_MAX,
- .get = data_from_kernel,
- };
-
- static int __init init(void)
- {
- return nf_register_sockopt(&imp1_sockops);
- }
-
- static void __exit fini(void)
- {
- nf_unregister_sockopt(&imp1_sockops);
- }
-
- module_init(init);
- module_exit(fini);
用户测试程序:
编译:gcc -o user imp1_u.c
/*imp1_u.c*/
- #include <unistd.h>
- #include <stdio.h>
- #include <sys/socket.h>
- #include <linux/in.h>
- #include "imp1.h"
-
- #define UMSG "a message from userspace/n"
- #define UMSG_LEN sizeof("a message from userspace/n")
-
- char kmsg[64];
-
- int main(void)
- {
- int sockfd;
- int len;
-
- sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
- if(sockfd < 0)
- {
- printf("can not create a socket/n");
- return -1;
- }
-
-
- setsockopt(sockfd, IPPROTO_IP, IMP1_SET, UMSG, UMSG_LEN);
-
- len = sizeof(char)*64;
-
-
- getsockopt(sockfd, IPPROTO_IP, IMP1_GET, kmsg, &len);
- printf("kmsg: %s", kmsg);
-
- close(sockfd);
- return 0;
- }
用insmod加载module
用rmmod删除module
用lsmod查看有没有加载成功
dmesg:
umsg: a message from userspace
umsg: a message from userspace
[root@localhost ipc_sockopt]# ./user
kmsg: a message from kernel
[root@localhost ipc_sockopt]# ./user
kmsg: a message from kernel
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