Linux下netlink通信的实例代码

Linux下netlink通信的实例代码
源代码共分三个文件：
内核模块：netlink-exam-kern.c
应用接收：netlink-exam-user-recv.c
应用发送：netlink-exam-user-send.c

内核模块源码：

//kernel module: netlink-exam-kern.c
#include <linux/config.h>
#include <linux/module.h>
#include <linux/netlink.h>
#include <linux/sched.h>
#include <net/sock.h>
#include <linux/proc_fs.h>

#define BUF_SIZE 16384
static struct sock *netlink_exam_sock;
static unsigned char buffer[BUF_SIZE];
static unsigned int buffer_tail = 0;
static int exit_flag = 0;
static DECLARE_COMPLETION(exit_completion);

static void recv_handler(struct sock * sk, int length)
{
wake_up(sk->sk_sleep);
}

static int process_message_thread(void * data)
{
struct sk_buff * skb = NULL;
struct nlmsghdr * nlhdr = NULL;
int len;
DEFINE_WAIT(wait);

daemonize("mynetlink");

while (exit_flag == 0) {
prepare_to_wait(netlink_exam_sock->sk_sleep, &wait, TASK_INTERRUPTIBLE);
schedule();
finish_wait(netlink_exam_sock->sk_sleep, &wait);

while ((skb = skb_dequeue(&netlink_exam_sock->sk_receive_queue))
!= NULL) {
nlhdr = (struct nlmsghdr *)skb->data;
if (nlhdr->nlmsg_len < sizeof(struct nlmsghdr)) {
printk("Corrupt netlink message.\n");
continue;
}
len = nlhdr->nlmsg_len - NLMSG_LENGTH(0);
if (len + buffer_tail > BUF_SIZE) {
printk("netlink buffer is full.\n");
}
else {
memcpy(buffer + buffer_tail, NLMSG_DATA(nlhdr), len);
buffer_tail += len;
}
nlhdr->nlmsg_pid = 0;
nlhdr->nlmsg_flags = 0;
NETLINK_CB(skb).pid = 0;
NETLINK_CB(skb).dst_pid = 0;
NETLINK_CB(skb).dst_group = 1;
netlink_broadcast(netlink_exam_sock, skb, 0, 1, GFP_KERNEL);
}
}
complete(&exit_completion);
return 0;
}

static int netlink_exam_readproc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
int len;

if (off >= buffer_tail) {
* eof = 1;
return 0;
}
else {
len = count;
if (count > PAGE_SIZE) {
len = PAGE_SIZE;
}
if (len > buffer_tail - off) {
len = buffer_tail - off;
}
memcpy(page, buffer + off, len);
*start = page;
return len;
}

}

static int __init netlink_exam_init(void)
{
netlink_exam_sock = netlink_kernel_create(NETLINK_GENERIC, 0, recv_handler, THIS_MODULE);
if (!netlink_exam_sock) {
printk("Fail to create netlink socket.\n");
return 1;
}
kernel_thread(process_message_thread, NULL, CLONE_KERNEL);
create_proc_read_entry("netlink_exam_buffer", 0444, NULL, netlink_exam_readproc, 0);
return 0;
}

static void __exit netlink_exam_exit(void)
{
exit_flag = 1;
wake_up(netlink_exam_sock->sk_sleep);
wait_for_completion(&exit_completion);
sock_release(netlink_exam_sock->sk_socket);
}

module_init(netlink_exam_init);
module_exit(netlink_exam_exit);
MODULE_LICENSE("GPL");

用户接收源码：

//application receiver: netlink-exam-user-recv.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/netlink.h>

#define MAX_MSGSIZE 1024

int main(void)
{
struct sockaddr_nl saddr, daddr;
struct nlmsghdr *nlhdr = NULL;
struct msghdr msg;
struct iovec iov;
int sd;
int ret = 1;

sd = socket(AF_NETLINK, SOCK_RAW,NETLINK_GENERIC);
memset(&saddr, 0, sizeof(saddr));
memset(&daddr, 0, sizeof(daddr));

saddr.nl_family = AF_NETLINK;
saddr.nl_pid = getpid();
saddr.nl_groups = 1;
bind(sd, (struct sockaddr*)&saddr, sizeof(saddr));

nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));

while (1) {
memset(nlhdr, 0, NLMSG_SPACE(MAX_MSGSIZE));

iov.iov_base = (void *)nlhdr;
iov.iov_len = NLMSG_SPACE(MAX_MSGSIZE);
msg.msg_name = (void *)&daddr;
msg.msg_namelen = sizeof(daddr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;

ret = recvmsg(sd, &msg, 0);
if (ret == 0) {
printf("Exit.\n");
exit(0);
}
else if (ret == -1) {
perror("recvmsg:");
exit(1);
}
printf("%s", NLMSG_DATA(nlhdr));
}

close(sd);
}

用户发送源码：

//application sender: netlink-exam-user-send.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/netlink.h>

#define MAX_MSGSIZE 1024

int main(int argc, char * argv[])
{
FILE * fp;
struct sockaddr_nl saddr, daddr;
struct nlmsghdr *nlhdr = NULL;
struct msghdr msg;
struct iovec iov;
int sd;
char text_line[MAX_MSGSIZE];
int ret = -1;

if (argc < 2) {
printf("Usage: %s atextfilename\n", argv[0]);
exit(1);
}

if ((fp = fopen(argv[1], "r")) == NULL) {
printf("File %s dosen't exist.\n");
exit(1);
}

sd = socket(AF_NETLINK, SOCK_RAW,NETLINK_GENERIC);
memset(&saddr, 0, sizeof(saddr));
memset(&daddr, 0, sizeof(daddr));

saddr.nl_family = AF_NETLINK;
saddr.nl_pid = getpid();
saddr.nl_groups = 0;
bind(sd, (struct sockaddr*)&saddr, sizeof(saddr));

daddr.nl_family = AF_NETLINK;
daddr.nl_pid = 0;
daddr.nl_groups = 0;

nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_MSGSIZE));

while (fgets(text_line, MAX_MSGSIZE, fp)) {
memcpy(NLMSG_DATA(nlhdr), text_line, strlen(text_line));
memset(&msg, 0 ,sizeof(struct msghdr));

nlhdr->nlmsg_len = NLMSG_LENGTH(strlen(text_line));
nlhdr->nlmsg_pid = getpid();  /* self pid */
nlhdr->nlmsg_flags = 0;

iov.iov_base = (void *)nlhdr;
iov.iov_len = nlhdr->nlmsg_len;
msg.msg_name = (void *)&daddr;
msg.msg_namelen = sizeof(daddr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
ret = sendmsg(sd, &msg, 0);
if (ret == -1) {
perror("sendmsg error:");
}
}

close(sd);
}