通过netlink实现内核模块和应用层通信

贴上代码，方便以后查阅。

skb常用操作函数，比较容易弄混

skb_put : skb->tail += len, skb->len += len
skb_pull: skb->data += len, skb->len -= len
skb_push: skb->data -= len, skb->len += len

内核版本linux2.6.38，编译环境gcc 4.4.4，centos6.0

内核模块代码：

/* * author: [e-mail] * date : 2011-10-29 */#include <linux/module.h>#include <linux/netlink.h>#include <linux/sched.h>#include <net/sock.h>#include <linux/proc_fs.h>#include <linux/netfilter.h>#include <linux/netfilter_ipv4.h>#include <linux/ip.h>#include <linux/tcp.h>#include <linux/icmp.h>#include <linux/udp.h>#define NETLINK_TEST 30/* 调试信息 */#define LOGMSG(fmt, arg...) \do{ \    printk("[func:%s,line:%d]: "fmt, __FUNCTION__, __LINE__, ##arg); \}while(0)/* 错误信息 */#define LOGERR(fmt, arg...) \do{ \    printk("[func:%s,line:%d]: "fmt, __FUNCTION__, __LINE__, ##arg); \}while(0)/* 断言 */#define ASSERT(expr) \if (unlikely(!(expr))) { \    printk("Assertion failed! %s,%s,%s,line=%d\n", \    #expr, __FILE__, __func__, __LINE__); \}/* 消息最大值 */#define MAX_MSG_LEN 1024enum{    NLMSG_TYPE_NONE = 0,    NLMSG_TYPE_SETPID,  /* 设置PID */    NLMSG_TYPE_KERNEL,  /* 消息来自内核 */    NLMSG_TYPE_APP,     /* 消息来自应用层 */};struct nlmsg{    int type;               /* 消息类型 */    int len;                /* 消息长度，包括头部 */    char msg[MAX_MSG_LEN];  /* 消息正文 */};/* netlink socket */static struct sock *g_nl_sk = NULL;static int g_nlpid = -1;    /* 应用层接收程序PID *//* * 发送整个从ip头开始的skb数据到应用层 *  * param[in]: sk, skb发送目的socket * param[in]: skb, 待发送的skb * return -1, 失败; 0, 成功 * */int nl_sendskb(struct sock *sk, struct sk_buff *skb){    struct iphdr *iph = NULL;    struct nlmsghdr *nlh = NULL;    struct sk_buff *nl_skb = NULL;    int skb_len = 0;    ASSERT(skb != NULL);    ASSERT(sk != NULL);    if(g_nlpid < 0)        return 0;    iph = ip_hdr(skb);    skb_len = iph->tot_len;    /* NLMSG_SPACE: sizeof(struct nlmsghdr) + len按4字节对齐 */    nl_skb = alloc_skb(NLMSG_SPACE(skb_len), GFP_ATOMIC);    if(!nl_skb)    {        LOGERR("nl_skb == NULL, failed!\n");        return -1;    }    /*     * static inline struct nlmsghdr *nlmsg_put(struct sk_buff *skb, u32 pid, u32 seq,     *               int type, int payload, int flags);     * 设置skb->tail指针指向skb->data + sizeof(struct nlmsghdr) + payload     * skb->len = sizeof(struct nlmsghdr) + payload      */    nlh = nlmsg_put(nl_skb, 0, 0, 0, NLMSG_SPACE(skb_len) - sizeof(struct nlmsghdr), 0);     NETLINK_CB(nl_skb).pid = 0; /* 0代表数据来自内核 */    memcpy(NLMSG_DATA(nlh), (char *)iph, htons(iph->tot_len));    /* 将数据发送给进程号22345的进程 */    return netlink_unicast(sk, nl_skb, g_nlpid , MSG_DONTWAIT);}/* * 发送字符串到应用层 * * param[in]: sk, 数据发往的socket * param[in]: pmsg, 待发送字符串 * param[in]: msglen, 待发送字符串长度 *  * return: -1, 失败; 0, 成功 * */int nl_sendmsg(struct sock *sk, struct nlmsg *pmsg){    struct nlmsghdr *nlh = NULL;    struct sk_buff *nl_skb = NULL;    int msglen = pmsg->len;    ASSERT(pmsg != NULL);    ASSERT(sk != NULL);    if(g_nlpid < 0)        return 0;    nl_skb = alloc_skb(NLMSG_SPACE(msglen), GFP_ATOMIC);    if(!nl_skb)    {        LOGERR("nl_skb == NULL, msglen = %d, failed!\n", msglen);        return -1;    }    nlh = nlmsg_put(nl_skb, 0, 0, 0,                     NLMSG_SPACE(msglen) - NLMSG_HDRLEN, 0);     NETLINK_CB(nl_skb).pid = 0;    memcpy(NLMSG_DATA(nlh), pmsg, msglen);    return netlink_unicast(sk, nl_skb, g_nlpid , MSG_DONTWAIT);}/*  * 从应用层接收数据, netlink_kernel_create注册的回调 * param[in]: skb, 包含netlink数据的skb * * skb常用操作函数 * skb_put : skb->tail += len, skb->len += len * skb_pull: skb->data += len, skb->len -= len * skb_push: skb->data -= len, skb->len += len */static void nl_recvmsg(struct sk_buff *skb){    struct nlmsg *pmsg = NULL;    struct nlmsghdr *nlh = NULL;    uint32_t rlen = 0;        while(skb->len >= NLMSG_SPACE(0))    {        nlh = nlmsg_hdr(skb);        if(nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len)            return;        rlen = NLMSG_ALIGN(nlh->nlmsg_len);        if(rlen > skb->len)            rlen = skb->len;        pmsg = (struct nlmsg*)NLMSG_DATA(nlh);        switch(pmsg->type)        {        case NLMSG_TYPE_SETPID:            g_nlpid = nlh->nlmsg_pid;            LOGMSG("pid: %d\n", g_nlpid);            LOGMSG("msg: %s\n", pmsg->msg);            break;        case NLMSG_TYPE_KERNEL:            break;        case NLMSG_TYPE_APP:            break;        }        /* 获取下一条netlink消息 */        skb_pull(skb, rlen);    }}/*  * netfilter PRE_ROUTING钩子 * */unsigned int pre_routing_hook(unsigned int hooknum,                            struct sk_buff *skb,                            const struct net_device *in,                           const struct net_device *out,                           int (*okfn)(struct sk_buff *)){    char *psend = "msg for kernel";    struct nlmsg msg;    int ret = 0;    msg.type = NLMSG_TYPE_KERNEL;    msg.len = strlen(psend) + offsetof(struct nlmsg, msg) + 1;    memcpy(msg.msg, psend, msg.len);    //ret = nl_sendskb(g_nl_sk, skb);    ret = nl_sendmsg(g_nl_sk, &msg);    //LOGMSG("ok\n");    return NF_ACCEPT;}static struct nf_hook_ops local_in_ops __read_mostly = {    .hook = pre_routing_hook,    .owner = THIS_MODULE,    .pf = PF_INET,    .hooknum = NF_INET_PRE_ROUTING,    .priority = NF_IP_PRI_FIRST};static int __init nl_init(void){    int ret = 0;    /*      * struct sock *netlink_kernel_create(struct net *net, int unit, unsigned int groups,     *                                    void (*input)(struct sk_buff *skb),     *                                    struct mutex *cb_mutex, struct module *module)     */    g_nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, 0, nl_recvmsg, NULL, THIS_MODULE);    if (!g_nl_sk) {        LOGERR("Fail to create netlink socket.\n");        return -1;    }    ret = nf_register_hook(&local_in_ops);    if(ret < 0)    {        LOGMSG("nf_register_hook failed!\n");        goto sock_release;    }    LOGMSG("ok!\n");    return 0;sock_release:    if(g_nl_sk)        sock_release(g_nl_sk->sk_socket);    return -1;}static void __exit nl_exit(void){    synchronize_sched();    if(g_nl_sk)        sock_release(g_nl_sk->sk_socket);    nf_unregister_hook(&local_in_ops);    LOGMSG("ok!\n");}module_init(nl_init);module_exit(nl_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("[e-mail]");

内核模块Makefile

module := netlinkobj-m := $(module).o#$(module)-objs :=  $(module).oKDIR=/root/kernel_newKHDR=/root/kernel_new/includeEXTRA_CFLAGS += $(FLAG) -I$(KHDR) -O2 -D__KERNEL__ -DMODULE $(INCLUDE) -DEXPORT_SYMTABCPPFLAGS += $(FLAG) -I$(KHDR)OUTDIR =TARGET = netlink.koTARGETDIR = /lib/modules/all:make -C $(KDIR) M=$(PWD) modulesclean:make -C $(KDIR) M=$(PWD) clean install: allinstall --verbose --mode=0755 $(OUTDIR)$(TARGET) $(INSTALLROOT)$(TARGETDIR)

应用层代码：

/* * author: [e-mail] * date : 2011-10-29 */#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 <stddef.h>#include <errno.h>   #define FREE_INIT(ptr) do{ \    free(ptr); \    ptr = NULL; \}while(0)/* 消息最大值 */#define MAX_MSG_LEN 1024enum{    NLMSG_TYPE_NONE = 0,    NLMSG_TYPE_SETPID,  /* 设置PID */    NLMSG_TYPE_KERNEL,  /* 消息来自内核 */    NLMSG_TYPE_APP,     /* 消息来自应用层 */};struct nlmsg{    int type;               /* 消息类型 */    int len;                /* 消息长度，包括头部 */    char msg[MAX_MSG_LEN];  /* 消息正文 */};#define NETLINK_TEST 30   /* * 打开netlink * return: 0, 成功; -1, 失败 * */int netlink_open(void){    struct sockaddr_nl saddr;    int sockfd = -1, ret = 0;        sockfd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TEST);      if(sockfd < -1){          perror("create socket!\n");        return -1;      }          memset(&saddr, 0, sizeof(saddr));      saddr.nl_family = PF_NETLINK;       saddr.nl_pid = getpid();    // self pid        saddr.nl_groups = 0;        // multi cast         ret = bind(sockfd, (struct sockaddr*)&saddr, sizeof(saddr));      if(ret < 0){          perror("bind failed!\n");          close(sockfd);          return -1;      }     return sockfd;}/* * 发送信息 * param[in]: sockfd * param[in]: pmsg, 待发送信息 *  * return: 0, 发送成功; -1: 发送失败 * */int netlink_send(int sockfd, struct nlmsg *pmsg){      struct msghdr msg;    struct iovec iov;    struct nlmsghdr *nlh = NULL;        int msglen = pmsg->len;    int totlen = NLMSG_SPACE(pmsg->len);    int ret = 0;        nlh = malloc(totlen);    if(!nlh)    {        fprintf(stderr, "malloc failed!\n");        return -1;    }    nlh->nlmsg_len = totlen;    nlh->nlmsg_flags = 0;    nlh->nlmsg_pid = getpid();        iov.iov_base = (void *)nlh;      iov.iov_len = nlh->nlmsg_len;        memset(&msg, 0, sizeof(msg));      msg.msg_iov = &iov;      msg.msg_iovlen = 1;             memcpy(NLMSG_DATA(nlh), pmsg, msglen);    ret = sendmsg(sockfd, &msg, 0);    if(ret < 0)    {        fprintf(stderr, "sendmsg failed!\n");        FREE_INIT(nlh);        return -1;    }    return 0;    }/* * 接收信息 * param[in]: sockfd * param[out]: pmsg *  * return 0, 成功; -1, 失败 * */int netlink_recv(int sockfd, struct nlmsg *pmsg){    struct msghdr msg;    struct iovec iov;    struct nlmsghdr *nlh = NULL;        int msglen = sizeof(*pmsg);    int totlen = NLMSG_SPACE(sizeof(*pmsg));    int ret = 0;        nlh = malloc(totlen);    if(!nlh)    {        fprintf(stderr, "malloc failed!\n");        return -1;    }        iov.iov_base = (void *)nlh;      iov.iov_len = totlen;        memset(&msg, 0, sizeof(msg));      msg.msg_iov = &iov;      msg.msg_iovlen = 1;         memcpy(NLMSG_DATA(nlh), pmsg, msglen);    ret = recvmsg(sockfd, &msg, 0);    if(ret < 0)    {        fprintf(stderr, "recvmsg failed!\n");        FREE_INIT(nlh);        return -1;    }    memcpy(pmsg, NLMSG_DATA(nlh), msglen);    return 0;}/*  * 关闭netlink * param[in]: sockfd, netlink socket号 * */void netlink_close(int sockfd){    if(sockfd > 0)        close(sockfd);}int main(int argc, char* argv[])  {      int sockfd = -1;    int ret = 0;    struct nlmsg msg;    char *psend = "msg from app!";        memset(&msg, 0, sizeof(msg));    /* 创建netlink socket */    sockfd = netlink_open();    if(sockfd < 0)    {        fprintf(stderr, "netlink_open failed!\n");        return -1;    }    /* 将进程号通知内核 */    msg.type = NLMSG_TYPE_SETPID;    msg.len = strlen(psend) + offsetof(struct nlmsg, msg) + 1;    memcpy(msg.msg, psend, strlen(psend));    ret = netlink_send(sockfd, &msg);    if(ret < 0)    {        fprintf(stderr, "netlink_send failed!\n");        return -1;    }    /* 接收消息 */    while(1)    {        ret = netlink_recv(sockfd, &msg);        if(ret < 0)        {            fprintf(stderr, "netlink_recv failed!\n");            return -1;        }        printf("msg: %s\n", msg.msg);    }    /* 关闭netlink */    netlink_close(sockfd);    return 0;  }