使用netlink机制在内核进程和用户空间进程通信
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内核模块代码:
netlink_drv.c
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <net/sock.h>
#include <net/netlink.h>
#define NETLINK_TEST 21
struct sock *nl_sk = NULL;
EXPORT_SYMBOL_GPL(nl_sk);
void nl_data_ready (struct sk_buff *__skb)
{
struct sk_buff *skb;
struct nlmsghdr *nlh;
u32 pid;
int rc;
int len = NLMSG_SPACE(1200);
char str[100];
//printk("net_link: data is ready to read.\n");
skb = skb_get(__skb);
if (skb->len >= NLMSG_SPACE(0)) {
nlh = nlmsg_hdr(skb);
//printk("net_link: recv %s.\n", (char *)NLMSG_DATA(nlh));
memset(str, 0, sizeof(str));
memcpy(str,NLMSG_DATA(nlh), sizeof(str));
pid = nlh->nlmsg_pid; /*pid of sending process */
//printk("Usrspace sender pid is %d, message is %s \n", pid, (char *)NLMSG_DATA(nlh));
kfree_skb(skb);
skb = alloc_skb(len, GFP_ATOMIC);
if (!skb){
printk(KERN_ERR "net_link: allocate failed.\n");
return;
}
nlh = nlmsg_put(skb,0,0,0,1200,0);
NETLINK_CB(skb).pid = 0; /* from kernel */
if (strstr(str, "open")) {
printk("@@@ Kernel receive open command from Userspace then send open to Userspace \n");
memcpy(NLMSG_DATA(nlh), "kernel receive open command", sizeof("kernel receive open command"));
} else if (strstr(str, "close")) {
printk("@@@ Kernel receive close command from Userspace then send close to Userspace \n");
memcpy(NLMSG_DATA(nlh), "kernel receive close command", sizeof("kernel receive close command"));
}
//printk("net_link: going to send.\n");
rc = netlink_unicast(nl_sk, skb, pid, MSG_DONTWAIT);
if (rc < 0) {
printk(KERN_ERR "net_link: can not unicast skb (%d)\n", rc);
}
//printk("net_link: send is ok.\n");
}
return;
}
static int test_netlink(void)
{
nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, 0, nl_data_ready, NULL, THIS_MODULE);
if (!nl_sk) {
printk(KERN_ERR "net_link: Can not create netlink socket.\n");
return -EIO;
}
printk("net_link: create socket ok.\n");
return 0;
}
int my_module_init(void)
{
test_netlink();
return 0;
}
void my_module_exit(void)
{
if (nl_sk != NULL){
sock_release(nl_sk->sk_socket);
}
printk("net_link: remove ok.\n");
}
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alex Xia");
module_init(my_module_init);
module_exit(my_module_exit);
用户空间应用程序代码:
netlink_app.c
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <string.h>
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/socket.h>
#define MAX_PAYLOAD 1024 /* maximum payload size*/
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
int sock_fd;
struct msghdr msg;
char str[100];
int main(int argc, char* argv[])
{
char c;
sock_fd = socket(PF_NETLINK, SOCK_RAW, 21);
nlh=(struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
while(1) {
memset(str, 0, sizeof(str));
memset(&msg, 0, sizeof(msg));
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid(); /* self pid */
src_addr.nl_groups = 0; /* not in mcast groups */
bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));
memset(&dest_addr, 0, sizeof(dest_addr));
dest_addr.nl_family = AF_NETLINK;
dest_addr.nl_pid = 0; /* For Linux Kernel */
dest_addr.nl_groups = 0; /* unicast */
nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
nlh->nlmsg_pid = getpid(); /* self pid */
nlh->nlmsg_flags = 0;
iov.iov_base = (void *)nlh;
iov.iov_len = nlh->nlmsg_len;
msg.msg_name = (void *)&dest_addr;
msg.msg_namelen = sizeof(dest_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf("Please input a char, which o:open, c:close, k:killed, e:exit \n");
c = getchar();
if ('o' == c) {
strcpy(NLMSG_DATA(nlh), "open");
printf("Sending open message ...\n");
sendmsg(sock_fd, &msg, 0);
memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
recvmsg(sock_fd, &msg, 0);
printf("Received message payload: %s\n",NLMSG_DATA(nlh));
memcpy(str, NLMSG_DATA(nlh), sizeof(str));
if (strstr(str, "please kill your process")) {
printf("<<< Userspace receive kill process message from kernel, please input k \n");
}
} else if ('c' == c) {
printf("Sending close message ...\n");
strcpy(NLMSG_DATA(nlh), "close");
sendmsg(sock_fd, &msg, 0);
printf("Close return to userspace \n");
} else if ('k' == c) {
printf("Sending killed message ...\n");
strcpy(NLMSG_DATA(nlh), "killed");
sendmsg(sock_fd, &msg, 0);
printf("Killed return to userspace \n");
} else if ('e' == c) {
break;
}
}
/* Close Netlink Socket */
close(sock_fd);
}
如此可以再内核进程和用户空间进程间直接实现进程通信。
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