Net-link Socket hanging issue

Question

I want to create a Net-link Socket Over which continuously sending of the data from the user space and continuously redirecting of the message from the kernel space to the user space. but it hangs. Please help or suggest the solution. If any one knows why this is happening please provide the solution.

the code i used in Kernel SPACE is

#include <linux/module.h>
#include <net/sock.h> 
#include <linux/netlink.h>
#include <linux/skbuff.h>

#define NETLINK_USER 31

struct sock *nl_sk = NULL;

static void hello_nl_recv_msg(struct sk_buff *skb)
{

    struct nlmsghdr *nlh;
    int pid;
    struct sk_buff *skb_out;
    int msg_size;
    char *msg;
    int res;

    printk(KERN_INFO "Entering: %s\n", __FUNCTION__);

    nlh = (struct nlmsghdr *)skb->data;
    printk(KERN_INFO "Netlink received msg payload:%s\n", (char *)nlmsg_data(nlh));
    pid = nlh->nlmsg_pid; /*pid of sending process */

    msg = (char *)nlmsg_data(nlh);
    msg_size = strlen(msg);

    skb_out = nlmsg_new(msg_size, 0);
    if (!skb_out) {
        printk(KERN_ERR "Failed to allocate new skb\n");
        return;
    }

    nlh = nlmsg_put(skb_out, 0, 0, NLMSG_DONE, msg_size, 0);
    NETLINK_CB(skb_out).dst_group = 0; /* not in mcast group */

    strncpy(nlmsg_data(nlh), msg, msg_size);

    res = nlmsg_unicast(nl_sk, skb_out, pid);
    if (res < 0)
        printk(KERN_INFO "Error while sending bak to user\n");
}

static int __init hello_init(void)
{

    printk("Entering: %s\n", __FUNCTION__);
    //nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, 0, hello_nl_recv_msg, NULL, THIS_MODULE);
    struct netlink_kernel_cfg cfg = {
        .input = hello_nl_recv_msg,
    };

    nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg);
    if (!nl_sk) {
        printk(KERN_ALERT "Error creating socket.\n");
        return -10;
    }

    return 0;
}

static void __exit hello_exit(void)
{

    printk(KERN_INFO "exiting hello module\n");
    netlink_kernel_release(nl_sk);
}

module_init(hello_init); module_exit(hello_exit);

MODULE_LICENSE("GPL");

the code for the user space is

#include <sys/socket.h>
#include <linux/netlink.h>

#define NETLINK_USER 31

#define MAX_PAYLOAD 1024 /* maximum payload size*/
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
int sock_fd;
struct msghdr msg;

void *print_message_function( void *ptr )
{
     printf("Sending message to kernel\n");
    sendmsg(sock_fd, &msg, 0);
}

void main()
{
     pthread_t thread1;
     const char *message1 = "Thread 1";
     int  iret1;

    /* Create independent threads each of which will execute function */



    sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USER);
    if (sock_fd < 0)
        return -1;

    memset(&src_addr, 0, sizeof(src_addr));
    src_addr.nl_family = AF_NETLINK;
    src_addr.nl_pid = getpid(); /* self pid */

    bind(sock_fd, (struct sockaddr *)&src_addr, sizeof(src_addr));

    memset(&dest_addr, 0, sizeof(dest_addr));
    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.nl_family = AF_NETLINK;
    dest_addr.nl_pid = 0; /* For Linux Kernel */
    dest_addr.nl_groups = 0; /* unicast */

    nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
    memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
    nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
    nlh->nlmsg_pid = getpid();
    nlh->nlmsg_flags = 0;

    strcpy(NLMSG_DATA(nlh), "Hello");

    iov.iov_base = (void *)nlh;
    iov.iov_len = nlh->nlmsg_len;
    msg.msg_name = (void *)&dest_addr;
    msg.msg_namelen = sizeof(dest_addr);
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    iret1 = pthread_create( &thread1, NULL, print_message_function, NULL);
     if(iret1)
     {
         fprintf(stderr,"Error - pthread_create() return code: %d\n",iret1);
         exit(EXIT_FAILURE);
     }

    printf("Waiting for message from kernel\n");

    while(1)
    {
        /* Read message from kernel */
        recvmsg(sock_fd, &msg, 0);
        printf("Received message payload: %s\n", NLMSG_DATA(nlh));
        close(sock_fd);
    }
}

Net-link Socket hanging issue

0 Answers0