linux 用户态和内核通信之Netlink

http://www.linuxidc.com/Linux/2011-07/39085p2.htm

之前参考这篇帖子练习了一下netlink,当时记得可以正常调试成功，今天在自己笔记本上ubuntu 12.04 上调试了一下，结果一直出现kernel panic, 调试了一下发现应该是出现在kernel 向用户空间发送消息的流程中。至今没调试成功，记录一下吧，抽时间在调试一下：

用户空间：

/* * netlink_user.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>#include <errno.h>#define NETLINK_TEST 25#define MAX_PAYLOAD 1024 // maximum payload sizeint main(int argc, char* argv[]){    int state;    struct sockaddr_nl src_addr, dest_addr;    struct nlmsghdr *nlh = NULL;    struct iovec iov;    struct msghdr msg;    int sock_fd, retval;    int state_smg = 0;    // Create a socket    sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_TEST);    if(sock_fd == -1){        printf("error getting socket: %s", strerror(errno));        return -1;    }    // To prepare binding    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; // multi cast    retval = bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));    if(retval < 0){        printf("bind failed: %s", strerror(errno));        close(sock_fd);        return -1;    }    // To prepare recvmsg    nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));    if(!nlh){        printf("malloc nlmsghdr error!\n");        close(sock_fd);        return -1;    }    memset(&dest_addr,0,sizeof(dest_addr));    dest_addr.nl_family = AF_NETLINK;    dest_addr.nl_pid = 0;    dest_addr.nl_groups = 0;    nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);    nlh->nlmsg_pid = getpid();    nlh->nlmsg_flags = 0;    strcpy(NLMSG_DATA(nlh),"Hello you!");    iov.iov_base = (void *)nlh;   iov.iov_len = NLMSG_SPACE(MAX_PAYLOAD);    // iov.iov_len = nlh->nlmsg_len;    memset(&msg, 0, sizeof(msg));      msg.msg_name = (void *)&dest_addr;    msg.msg_namelen = sizeof(dest_addr);    msg.msg_iov = &iov;    msg.msg_iovlen = 1;    printf("state_smg\n");    state_smg = sendmsg(sock_fd,&msg,0);    if(state_smg == -1)    {        printf("get error sendmsg = %s\n",strerror(errno));    }    memset(nlh,0,NLMSG_SPACE(MAX_PAYLOAD));    printf("waiting received!\n");    // Read message from kernel    while(1){        printf("In while recvmsg\n");        state = recvmsg(sock_fd, &msg, 0);        if(state<0)        {            printf("state<1");        }        printf("In while\n");        printf("Received message: %s\n",(char *) NLMSG_DATA(nlh));    }    close(sock_fd);    return 0;}

内核空间：

/* * netlink_kernel.c */#include <linux/init.h>#include <linux/module.h>#include <linux/timer.h>#include <linux/time.h>#include <linux/types.h>#include <net/sock.h>#include <net/netlink.h>#define NETLINK_TEST 25#define MAX_MSGSIZE 1024int stringlength(char *s);void sendnlmsg(char* message);int pid;int err;struct sock *nl_sk = NULL;int flag = 0;void sendnlmsg(char* message){    struct sk_buff *skb_1;    struct nlmsghdr *nlh;    int len = NLMSG_SPACE(MAX_MSGSIZE);    int slen = 0;        if(!message || !nl_sk)    {        return ;    }        skb_1 = alloc_skb(len,GFP_KERNEL);        if(!skb_1)    {        printk(KERN_ERR "my_net_link:alloc_skb_1 error\n");    }        slen = stringlength(message);    nlh = nlmsg_put(skb_1,0,0,0,MAX_MSGSIZE,0);    NETLINK_CB(skb_1).pid = 0;    NETLINK_CB(skb_1).dst_group = 0;message[slen]= '\0';memcpy(NLMSG_DATA(nlh),message,slen+1);printk("my_net_link:send message '%s'.\n",(char *)NLMSG_DATA(nlh));    netlink_unicast(nl_sk,skb_1,pid,MSG_DONTWAIT);}int stringlength(char *s){    int slen = 0;    for(; *s; s++){        slen++;    }    return slen;}void nl_data_ready(struct sk_buff *__skb) {struct sk_buff *skb;struct nlmsghdr *nlh;char str[100];struct completion cmpl;int i=10;printk(KERN_ALERT "entering nl_data_ready\n");skb = skb_get (__skb);if(skb->len >= NLMSG_SPACE(0)){nlh = nlmsg_hdr(skb);memcpy(str, NLMSG_DATA(nlh), sizeof(str));printk("Message received:%s\n",str) ;pid = nlh->nlmsg_pid;printk(KERN_ALERT "pid is: %d\n",pid);/*while(i--){init_completion(&cmpl);wait_for_completion_timeout(&cmpl,3 * HZ);sendnlmsg("I am from kernel!");}*///NETLINK_CB(skb).groups = 0; /* not in mcast group */NETLINK_CB(skb).pid = 0;      /* from kernel *///NETLINK_CB(skb).dst_pid = pid;NETLINK_CB(skb).dst_group = 0;  /* unicast */    //netlink_unicast(nl_sk,skb,pid,MSG_DONTWAIT);flag = 1;kfree_skb(skb);    } }// Initialize netlinkint netlink_init(void){    nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, 1,                                 nl_data_ready, NULL, THIS_MODULE);    if(!nl_sk){        printk(KERN_ERR "my_net_link: create netlink socket error.\n");        return 1;    }    printk("my_net_link_3: create netlink socket ok.\n");    return 0;}static void netlink_exit(void){    if(nl_sk != NULL){        sock_release(nl_sk->sk_socket);    }    printk("my_net_link: self module exited\n");}module_init(netlink_init);module_exit(netlink_exit);MODULE_AUTHOR("xxxxxxx");MODULE_LICENSE("GPL");

Makefile:

obj-m := netlink_kernel.oKERNELBUILD := /lib/modules/`uname -r`/builddefault:@echo "BUILE Kmod"@make -C $(KERNELBUILD) M=$(shell pwd)gcc -o netlink_user netlink_user.cclean:@echo " CLEAN kmod"@rm -rf *.o@rm -rf .depend .*.cmd *.ko *.mod.c .tmp_versions *.symvers .*.d