chlclan

thanks for your article it is very useful . i try to create communication socket beetwin Kernel module and user land program . i used you proposed code . but it is not worked correctly . i compile my module and userland code correctly but there is no communication between them .
please , It would be nice if you could add working or at least compilable examples.

best regard's
M.taghiloo

thanks for your article it is very useful . i try to create communication socket beetwin Kernel module and user land program . i used you proposed code . but it is not worked correctly . i compile my module and userland code correctly but there is no communication between them .
please , It would be nice if you could add working or at least compilable examples.

best regard's
M.taghiloo

thanks for your article it is very useful . i try to create communication socket beetwin Kernel module and user land program . i used you proposed code . but it is not worked correctly . i compile my module and userland code correctly but there is no communication between them .
please , It would be nice if you could add working or at least compilable examples.

best regard's
M.taghiloo

/* Working version of the Netlink Socket code from Linux Journal's Kernel Korner */
#include
#include
#include
#include
#include
#include

#define MAX_PAYLOAD 1024
struct sockaddr_nl src_addr, dst_addr;
struct nlmsghdr *nlh = NULL;
struct msghdr msg;
struct iovec iov;
int sock_fd;

int main()
{
sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_NITRO);

memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
src_addr.nl_groups = 0; // no multicast
bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));

memset(&dst_addr, 0, sizeof(dst_addr));
dst_addr.nl_family = AF_NETLINK;
dst_addr.nl_pid = 0; // 0 means kernel
dst_addr.nl_groups = 0; // no multicast

nlh = (struct nlhmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));

/* Fill the netlink message header */
nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
nlh->nlmsg_pid = getpid();
nlh->nlmsg_flags = 0;

strcpy(NLMSG_DATA(nlh), "Yoo-hoo, Mr. Kernel!");

iov.iov_base = (void *)nlh;
iov.iov_len = nlh->nlmsg_len;

msg.msg_name = (void *)&dst_addr;
msg.msg_namelen = sizeof(dst_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;

sendmsg(sock_fd, &msg, 0);

/* Read message from kernel */
memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
recvmsg(sock_fd, &msg, 0);
printf("Received message payload: %s\n", NLMSG_DATA(nlh));

close(sock_fd);

return (EXIT_SUCCESS);

}

/* The Linux Journal Kernel Korner -- Working, compiling version of the kernel code */
#include
#include
#include
#include
#include
#include
#include

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Daniel Purcell");
MODULE_DESCRIPTION("Kernel Korner's working versinon of netlink sockets");

// Note: Debug is not implemented
static int debug = 0;

module_param(debug, int, 0);
MODULE_PARM_DESC(debug, "Debug information (default 0)");

static struct sock *nl_sk = NULL;

static void nl_data_ready (struct sock *sk, int len)
{
wake_up_interruptible(sk->sk_sleep);
}

static void netlink_test()
{
struct sk_buff *skb = NULL;
struct nlmsghdr *nlh = NULL;
int err;
u32 pid;

nl_sk = netlink_kernel_create(NETLINK_NITRO, nl_data_ready);
skb = skb_recv_datagram(nl_sk, 0, 0, &err);

nlh = (struct nlmsghdr *)skb->data;
printk(KERN_INFO "%s: received netlink message payload: %s\n", __FUNCTION__, NLMSG_DATA(nlh));

pid = nlh->nlmsg_pid;
NETLINK_CB(skb).groups = 0;
NETLINK_CB(skb).pid = 0;
NETLINK_CB(skb).dst_pid = pid;
NETLINK_CB(skb).dst_groups = 0;
netlink_unicast(nl_sk, skb, pid, MSG_DONTWAIT);
sock_release(nl_sk->sk_socket);
}

static int __init my_module_init(void)
{
printk(KERN_INFO "Initializing Netlink Socket");
netlink_test();
return 0;
}

static void __exit my_module_exit(void)
{
printk(KERN_INFO "Goodbye");
}

module_init(my_module_init);
module_exit(my_module_exit);

Hello,
The article is very clear and understood. It describes the advantages of using netlink sockets. I suppose it might be very useful in inter processes / threads communication in user-space application. But regarding the kernel space, there are disadvantages such as:
1. Kernel recompiling, because it requires netlink.h update.
2. Because it's running in the context of sendmsg prosses, the trivial ioctl is preferred just in the reason that it's not so sophisticated.
Any comments are very welcome,
Regards,
Michael

I hear that netlink provides support for communication within two different subsystems of the kernel. Wish this article had covered that.

RP

It would be nice if you could add working or at least compilable examples.

thanks,
-M