netlink示例程序：监听网络状态变化

下面的示例程序通过监听内核的netlink消息来获得网络接口的状态变化，比如插拔网线，获得IP地址等。

Makefile:

PROG=netlink
OBJS=netlink.o
CFLAGS =
LDFLAGS=-static
NDK_HOME ?=/opt/android-ndk-r9d


ifeq ($(ARM),1)
SYSROOT=$(NDK_HOME)/platforms/android-19/arch-arm/
CC=$(NDK_HOME)/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc --sysroot=$(SYSROOT)
PROG=netlink.arm
OBJS:=$(OBJS:.o=.arm.o)
else
ifeq ($(ndk),1)
SYSROOT=$(NDK_HOME)/platforms/android-19/arch-x86/
CC=$(NDK_HOME)/toolchains/x86-4.8/prebuilt/linux-x86_64/bin/i686-linux-android-gcc --sysroot=$(SYSROOT)
endif

ifeq ($(DEBUG),1)
CFLAGS += -g -ggdb
endif

#CFLAGS += -m32
#LDFLAGS += -m32

endif

all: $(PROG)

netlink: $(OBJS)
	$(CC) $(LDFLAGS) -o $@ $^

netlink.arm: $(OBJS)
	$(CC) $(LDFLAGS) -o $@ $^

%.o:%.c
	$(CC) $(CFLAGS) -c -o $@ $<

%.arm.o:%.c
	$(CC) $(CFLAGS) -c -o $@ $<

clean:
	rm -rf *.o netlink netlink.arm 

netlink.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 
#include 
//#include 
#include 

#include 

FILE* fp=NULL;
int running = 1;

void nl_log(const char* fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	if(fp != NULL){
		if (vfprintf(fp, fmt, ap) < 0){
			perror("fprintf");
		}
		fflush(fp);
	}
	vprintf(fmt, ap);
	va_end(ap);
}

void parseBinaryNetlinkMessage(struct nlmsghdr *nh) {
    int len = nh->nlmsg_len - sizeof(*nh);
    struct ifinfomsg *ifi;

    if (sizeof(*ifi) > (size_t) len) {
        nl_log("Got a short RTM_NEWLINK message\n");
        return;
    }

    ifi = (struct ifinfomsg *)NLMSG_DATA(nh);
    if ((ifi->ifi_flags & IFF_LOOPBACK) != 0) {
        return;
    }

    struct rtattr *rta = (struct rtattr *)
      ((char *) ifi + NLMSG_ALIGN(sizeof(*ifi)));
    len = NLMSG_PAYLOAD(nh, sizeof(*ifi));

    while(RTA_OK(rta, len)) {
        switch(rta->rta_type) {
          case IFLA_IFNAME:
          {
            char ifname[IFNAMSIZ];
	        char *action;
            snprintf(ifname, sizeof(ifname), "%s",
                     (char *) RTA_DATA(rta));
            //action = (ifi->ifi_flags & IFF_LOWER_UP) ? "up" : "down";
            action = (ifi->ifi_flags & IFF_RUNNING) ? "up" : "down";
	        nl_log("%s link %s\n", ifname, action);
          }
        }

        rta = RTA_NEXT(rta, len);
    }
}

void parseNetlinkAddrMsg(struct nlmsghdr *nlh, int new)
{
	struct ifaddrmsg *ifa = (struct ifaddrmsg *) NLMSG_DATA(nlh);
	struct rtattr *rth = IFA_RTA(ifa);
	int rtl = IFA_PAYLOAD(nlh);

	while (rtl && RTA_OK(rth, rtl)) {
	    if (rth->rta_type == IFA_LOCAL) {
		uint32_t ipaddr = htonl(*((uint32_t *)RTA_DATA(rth)));
		char name[IFNAMSIZ];
		if_indextoname(ifa->ifa_index, name);
		nl_log("%s %s address %d.%d.%d.%d\n",
		       name, (new != 0)?"add":"del",
		       (ipaddr >> 24) & 0xff,
		       (ipaddr >> 16) & 0xff,
		       (ipaddr >> 8) & 0xff,
		       ipaddr & 0xff);
	    }
	    rth = RTA_NEXT(rth, rtl);
	}
}

void signal_handle(int signo)
{
	nl_log("got signal:%d\n", signo);
	if(fp != NULL){
		fclose(fp);
	}
	exit(0);
}

int main(int argc, char* argv[])
{
    struct sockaddr_nl addr;
    int sock, len;
    char buffer[4096];
    struct nlmsghdr *nlh;
	char* fname = "netlink.log";

	if (argc > 1 && strcmp(argv[1],"-f")==0){
		fp = fopen(fname, "w");
		if (fp == NULL){
			perror("fopen");
			return 1;
		}
		printf("netlink message will also write to %s. \n", fname);
	}

	signal(SIGINT, signal_handle);
    if ((sock = socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) == -1) {
        perror("couldn't open NETLINK_ROUTE socket");
        return 1;
    }

    memset(&addr, 0, sizeof(addr));
    addr.nl_family = AF_NETLINK;
    addr.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR;

    if (bind(sock, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
        perror("couldn't bind");
        return 1;
    }

    while (running && (len = recv(sock, buffer, 4096, 0)) > 0) {
        nlh = (struct nlmsghdr *)buffer;
        while ((NLMSG_OK(nlh, len)) && (nlh->nlmsg_type != NLMSG_DONE)) {
            if (nlh->nlmsg_type == RTM_NEWADDR) {
				parseNetlinkAddrMsg(nlh, 1);
            }else if(nlh->nlmsg_type == RTM_DELADDR){
				parseNetlinkAddrMsg(nlh, 0);
            }else if (nlh->nlmsg_type == RTM_NEWLINK){
				parseBinaryNetlinkMessage(nlh);
			}
            nlh = NLMSG_NEXT(nlh, len);
        }
    }
	close(sock);
	if(fp != NULL){
		fclose(fp);
	}
    return 0;
}