Linux之netlink学习

这几天抓着个机会和时间, 了解了下 netlink 这个东东.今天晚上也刚把打印出来.准备没事的时候看看.进一步加深对netlink的了解.

 

多谢 chinaunix 这个平台, 提供了如此多的资料, 让我知道自己有哪些不知道, 然后拼了老命的学习.这里附上几个链接,因为我的学习,很多都是基于这几个链接.

  duanjigang的精华帖.

  独孤九贱的帖子.

我花了大概半天的时间, 把 《Linux 系统内核空间与用户空间通信的实现与分析》陈鑫 中间提到的代码, 移植到了 Linux 2.6.32 上.<发现, Linux内核变化确实挺快的.>

这次先贴上我修改过后的代码, 有空再来补补注释.^_^.

1. 将 imp2_k_my.c 编译成 ko, 然后 insmod 到系统.
2. 将 imp2_u.c 编译成应用程序.(我这里编译为 imp2_u. gcc imp2_u.c -o imp2_u.)
3. 将 imp2_u 程序后台运行. (./imp2_u &)
4. 执行一条ping命令. 可以看到 imp2_u 的打印. 和驱动的打印(dmesg | tail -10).

imp2.h

/*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

imp2_k_my.c

#ifndef __KERNEL__
#define __KERNEL__
#endif

#ifndef MODULE
#define MODULE
#endif

#include <linux/netfilter.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/netfilter_ipv4.h>
#include <linux/inet.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/netlink.h>
#include <linux/spinlock.h>
#include <net/sock.h>

#include "imp2.h"

MODULE_LICENSE("Dual BSD/GPL");

#define IMP2_K_MY "imp2_k_my:"
//#define printk(arg) //printkk(KERN_ALERT IMP2_K_MY arg)

DECLARE_MUTEX(receive_sem);
static struct sock *mysock;

struct
{
    __u32 pid;
    rwlock_t lock;
} user_proc;

static int send_to_user(struct packet_info *info)
{
    int ret = 0;
    int size;
    unsigned char *old_tail;

    struct sk_buff *skb;
    struct nlmsghdr *nlh;
    struct packet_info *packet;

    printk("%s, begin !!! \n", __func__);

    size = NLMSG_SPACE(sizeof(*info));

    skb = alloc_skb(size, GFP_ATOMIC);
    old_tail = skb->tail;

    nlh = NLMSG_PUT(skb, 0, 0, IMP2_K_MSG, size - sizeof(*nlh));
    packet = NLMSG_DATA(nlh);
    memset(packet, 0, sizeof(struct packet_info));

    packet->src = info->src;
    packet->dest = info->dest;

    nlh->nlmsg_len = skb->tail - old_tail;
    NETLINK_CB(skb).dst_group = 0;

    read_lock_bh(&user_proc.lock);
    ret = netlink_unicast(mysock, skb, user_proc.pid, MSG_DONTWAIT);
    read_unlock_bh(&user_proc.lock);

    printk("%s, end !!! \n", __func__);

    return ret;

nlmsg_failure:
    if(skb)
        kfree_skb(skb);
    return -1;
}

static unsigned int icmp_hook_func(unsigned int hooknum,
             struct sk_buff *skb,
             const struct net_device *in,
             const struct net_device *out,
             int (*okfn)(struct sk_buff *))
{
    struct iphdr *iph = ip_hdr(skb);
    struct packet_info info;

    //printk("%s, begin !!! \n", __func__);

    if (iph->protocol == IPPROTO_ICMP) {
        read_lock_bh(&user_proc.lock);

        if (user_proc.pid != 0) {
            info.src = iph->saddr;
            info.dest = iph->daddr;
            printk("%s, src=%u.%u.%u.%u, dst=%u.%u.%u.%u\n", __func__,
                NIPQUAD(info.src), NIPQUAD(info.dest));
            send_to_user(&info);
        } else {
            printk("%s, no user process running..!\n", __func__);
        }

        read_unlock_bh(&user_proc.lock);
    }
    //printk("%s, end !!! \n", __func__);

    return NF_ACCEPT;
}

#define NF_IP_PRE_ROUTING    0

static struct nf_hook_ops my_icmp_hook = {
    .hook = icmp_hook_func,
    .pf = PF_INET,
    .hooknum = NF_IP_PRE_ROUTING,
    .owner = THIS_MODULE,
    .priority = NF_IP_PRI_FILTER - 1,
};

static void my_receive(struct sk_buff *skb)
{
    struct nlmsghdr *nlh;
    int len;

    printk("%s, begin !!!!!\n", __func__);

    nlh = nlmsg_hdr(skb);
    len = skb->len;

    while (NLMSG_OK(nlh, len)) {

        printk("%s, skb_len = %d!!!!!\n", __func__, len);

        write_lock_bh(&user_proc.pid);
        if (nlh->nlmsg_type == IMP2_U_PID) {
            user_proc.pid = nlh->nlmsg_pid;
        } else if (nlh->nlmsg_type == IMP2_CLOSE &&
                nlh->nlmsg_pid == user_proc.pid) {
            user_proc.pid = 0;
        }
        write_unlock_bh(&user_proc.pid);

        netlink_ack(skb, nlh, 0);
        nlh = NLMSG_NEXT(nlh, len);
    }

    printk("%s, end !!!!!\n", __func__);
}

static int __init imp2_k_my_init(void)
{
    printk("%s, begin !!!!!\n", __func__);

    rwlock_init(&user_proc.lock);

    mysock = netlink_kernel_create(&init_net, NL_IMP2, 0, my_receive,
        NULL, THIS_MODULE);
    if (!mysock) {
        printk("%s, netlink_kernel_create fail.. !!!!!\n", __func__);
        return -1;
    }

    printk("%s, end !!!!!\n", __func__);

    return nf_register_hook(&my_icmp_hook);
}

static void __exit imp2_k_my_exit(void)
{
    printk("%s, begin !!!!!\n", __func__);
    netlink_kernel_release(mysock);
    nf_unregister_hook(&my_icmp_hook);
    printk("%s, end !!!!!\n", __func__);
}

module_init(imp2_k_my_init);
module_exit(imp2_k_my_exit);

 

用户态程序:

#include <unistd.h>
#include <stdio.h>
#include <linux/types.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <asm/types.h>
#include <linux/netlink.h>
#include <signal.h>
#include "imp2.h"

struct msg_to_kernel
{
    struct nlmsghdr hdr;
};

struct u_packet_info
{
  struct nlmsghdr hdr;
  struct packet_info icmp_info;
};

static int skfd;

static void sig_int(int signo)
{
    struct sockaddr_nl kpeer;
    struct msg_to_kernel message;

    memset(&kpeer, 0, sizeof(kpeer));
    kpeer.nl_family = AF_NETLINK;
    kpeer.nl_pid = 0;
    kpeer.nl_groups = 0;

    memset(&message, 0, sizeof(message));
    message.hdr.nlmsg_len = NLMSG_LENGTH(0);
    message.hdr.nlmsg_flags = 0;
    message.hdr.nlmsg_type = IMP2_CLOSE;
    message.hdr.nlmsg_pid = getpid();

    sendto(skfd, &message, message.hdr.nlmsg_len, 0, (struct sockaddr *)(&kpeer),
         sizeof(kpeer));

    close(skfd);
    exit(0);
}

int main(void)
{
    struct sockaddr_nl local;
    struct sockaddr_nl kpeer;
    int kpeerlen;
    struct msg_to_kernel message;
    struct u_packet_info info;
    int sendlen = 0;
    int rcvlen = 0;
    struct in_addr addr;

    skfd = socket(PF_NETLINK, SOCK_RAW, NL_IMP2);
    if(skfd < 0) {
        printf("can not create a netlink socket\n");
        exit(0);
    }

    memset(&local, 0, sizeof(local));
    local.nl_family = AF_NETLINK;
    local.nl_pid = getpid();
    local.nl_groups = 0;
    if(bind(skfd, (struct sockaddr*)&local, sizeof(local)) != 0) {
        printf("bind() error\n");
        return -1;
    }

    signal(SIGINT, sig_int);

    memset(&kpeer, 0, sizeof(kpeer));
    kpeer.nl_family = AF_NETLINK;
    kpeer.nl_pid = 0;
    kpeer.nl_groups = 0;

    memset(&message, 0, sizeof(message));
    message.hdr.nlmsg_len = NLMSG_LENGTH(0);
    message.hdr.nlmsg_flags = 0;
    message.hdr.nlmsg_type = IMP2_U_PID;
    message.hdr.nlmsg_pid = local.nl_pid;

    sendto(skfd, &message, message.hdr.nlmsg_len, 0,
        (struct sockaddr*)&kpeer, sizeof(kpeer));

    while(1) {
        kpeerlen = sizeof(struct sockaddr_nl);
        rcvlen = recvfrom(skfd, &info, sizeof(struct u_packet_info),
        0, (struct sockaddr*)&kpeer, &kpeerlen);

        addr.s_addr = info.icmp_info.src;
        printf("src: %s, ", inet_ntoa(addr));
        addr.s_addr = info.icmp_info.dest;
        printf("dest: %s\n", inet_ntoa(addr));
    }

    return 0;
}