Linux系统内核空间与用户空间通信的实现与分析

static struct sock *nlfd;struct{  __u32 pid;  rwlock_t lock;}user_proc;/*挂接在 netfilter 框架的 NF_IP_PRE_ROUTING 点上的函数为 get_icmp()*/static struct nf_hook_ops imp2_ops ={  .hook = get_icmp,/*netfilter 钩子函数*/  .pf = PF_INET,  .hooknum = NF_IP_PRE_ROUTING,  .priority = NF_IP_PRI_FILTER -1,};static int __init init(void){  rwlock_init(&user_proc.lock);  /*在内核创建一个 netlink socket，并注明由 kernel_recieve() 函数接收数据    这里协议 NL_IMP2 是自定的*/  nlfd = netlink_kernel_create(NL_IMP2, kernel_receive);  if(!nlfd)    {      printk("can not create a netlink socket/n");      return -1;    }  /*向 netfilter 的 NF_IP_PRE_ROUTING 点挂接函数*/  return nf_register_hook(&imp2_ops);}static void __exit fini(void){  if(nlfd)    {      sock_release(nlfd->socket);}  nf_unregister_hook(&imp2_ops);}module_init(init);module_exit(fini);

DECLARE_MUTEX(receive_sem);01:static void kernel_receive(struct sock *sk, int len)02:{03:  do04:    {05:     struct sk_buff *skb;06:      if(down_trylock(&receive_sem))07:        return;08:09:      while((skb = skb_dequeue(&sk-

static unsigned int get_icmp(unsigned int hook,                             struct sk_buff **pskb,                             const struct net_device *in,                             const struct net_device *out,                             int (*okfn)(struct sk_buff *)){  struct iphdr *iph = (*pskb)->nh.iph;  struct packet_info info;  if(iph->protocol == IPPROTO_ICMP)/*若传输层协议为 ICMP*/    {      read_lock_bh(&user_proc.lock);      if(user_proc.pid != 0)    {          read_unlock_bh(&user_proc.lock);          info.src = iph->saddr;/*记录源地址*/          info.dest = iph->daddr;/*记录目的地址*/          send_to_user(&info);/*发送数据*/        }      else        read_unlock_bh(&user_proc.lock);    }  return NF_ACCEPT;}

static int send_to_user(struct packet_info *info){  int ret;  int size;  unsigned char *old_tail;  struct sk_buff *skb;  struct nlmsghdr *nlh;  struct packet_info *packet;  size = NLMSG_SPACE(sizeof(*info));  /*开辟一个新的套接字缓存*/  skb = alloc_skb(size, GFP_ATOMIC);  old_tail = skb->tail;  /*填写数据报相关信息*/  nlh = NLMSG_PUT(skb, 0, 0, IMP2_K_MSG, size-sizeof(*nlh));  packet = NLMSG_DATA(nlh);  memset(packet, 0, sizeof(struct packet_info));  /*传输到用户空间的数据*/  packet->src = info->src;  packet->dest = info->dest;  /*计算经过字节对其后的数据实际长度*/  nlh->nlmsg_len = skb->tail - old_tail;  NETLINK_CB(skb).dst_groups = 0;  read_lock_bh(&user_proc.lock);  ret = netlink_unicast(nlfd, skb, user_proc.pid, MSG_DONTWAIT); /*发送数据*/  read_unlock_bh(&user_proc.lock);  return ret; nlmsg_failure: /*若发送失败，则撤销套接字缓存*/  if(skb)    kfree_skb(skb);  return -1;}

/*字节对齐*/#define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )/*计算包含报头的数据报长度*/#define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(sizeof(struct nlmsghdr)))/*字节对齐后的数据报长度*/#define NLMSG_SPACE(len) NLMSG_ALIGN(NLMSG_LENGTH(len))/*填写相关报头信息，这里使用了nlmsg_failure标签，所以在程序中要定义*/#define NLMSG_PUT(skb, pid, seq, type, len) /({ if (skb_tailroom(skb) <(int)NLMSG_SPACE(len)) goto nlmsg_failure; /   __nlmsg_put(skb, pid, seq, type, len); })static __inline__ struct nlmsghdr *__nlmsg_put(struct sk_buff *skb, u32 pid, u32 seq, int type, int len){struct nlmsghdr *nlh;int size = NLMSG_LENGTH(len);nlh = (struct nlmsghdr*)skb_put(skb, NLMSG_ALIGN(size));nlh->nlmsg_type = type;nlh->nlmsg_len = size;nlh->nlmsg_flags = 0;nlh->nlmsg_pid = pid;nlh->nlmsg_seq = seq;return nlh;}/*跳过报头取实际数据*/#define NLMSG_DATA(nlh)  ((void*)(((char*)nlh) + NLMSG_LENGTH(0)))/*取 netlink 控制字段*/#define NETLINK_CB(skb)(*(struct netlink_skb_parms*)&((skb)->cb))