Question

While creating a netlink socket using netlink_kernel_create() a function pointer is passed as argument to this function which is called when a message is received on this socket. This call back function receives an sk_buff as parameter which contains the message received.

My question is that whose responsibility is it to free this sk_buff?

Example Code

#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 my_nl_recv_msg(struct sk_buff *skb) {

struct nlmsghdr *nlh;  
int pid;  

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 */  
NETLINK_CB(skb).dst_group = 0; /* not in mcast group */  
NETLINK_CB(skb).pid = 0;      /* from kernel */  
//printk("About to send msg bak:\n");  
//netlink_unicast(nl_sk,skb,pid,MSG_DONTWAIT);

}

static int __init hello_init(void) {

printk("Entering: %s\n",__FUNCTION__);  
nl_sk=netlink_kernel_create(&init_net, NETLINK_USER, 0,  
        my_nl_recv_msg, NULL, THIS_MODULE);  
if(!nl_sk)  
{  
    printk(KERN_ALERT "Error creating socket.\n");  
    return -10;  
}  
return 0;

}

Answer 1

net/netlink/af_netlink.c:netlink_unicast_kernel, the caller of your my_nl_recv_msg function will take care of freeing it.