How can I get these packets in the user space application?

Srinivas G. srinivasg at
Wed Dec 8 15:01:18 CET 2004

Dear all,

I have developed a very simple/small net filter driver to capture the
network packets from my network path. It was working fine. Whenever a
packet goes through my network path it was simply prints a message. It
was printing the messages fine.

The kernel version is 2.4.18-3 with Red Hat 7.3

My question is: How can I get these packets in the user space
What APIs can I use? Is there any specific APIs are available? If
possible give some links or sample code which explains about it.

Please see the code attached below.


#include <linux/module.h>		/* for module parameters */
#include <linux/kernel.h>		/* for printk function */
#include <linux/init.h>			/* for module explicit
definitions */
#include <linux/netfilter.h>		/* for netfilter structure */
#include <linux/netfilter_ipv4.h>	/* for IPv4 specific defines */
#include <linux/vmalloc.h>		/* for vmalloc function */

#define PRINTK(fmt,arg...) printk("NET_DBG <%s> | "
fmt,__FUNCTION__,##arg); #else #define PRINTK(fmt,arg...) while(0)

/* define the maximum packet buffer */
#define MAX_PACK_BUFF   2048

MODULE_AUTHOR("Srinivas G at ESN Technologies");

/* define netfilter structure here */
static struct nf_hook_ops netfilter_hook;

/* pointer to a buffer */
unsigned char *ptr_packet_buff;

/* function prototype which is called when a packet arrives */ unsigned
int netfilter_drv_hook(unsigned int hooknum, 
				struct sk_buff **skb,
		      		const struct net_device *in, 
				const struct net_device *out,
		      		int (*okfn)(struct sk_buff *))
	PRINTK("One Packet arrvied!\n");

	/* alocate the packet buffer */
	ptr_packet_buff = (unsigned char *)vmalloc(MAX_PACK_BUFF);
	/* the received packet was dropped here itself */
	return NF_DROP;

/* netfilter_init: initialization function */
static int
__init init_netfilter(void)
	/* assign the function pointer */
	netfilter_hook.hook = netfilter_drv_hook;

	/* assign the protocol family i.e. IPv4 */ = PF_INET;

	/* assign the hook number like NF_IP_LOCAL_IN etc. */
	netfilter_hook.hooknum = NF_IP_PRE_ROUTING;

	/* assign the hook priority */
	netfilter_hook.priority = NF_IP_PRI_FIRST;

	/* register the netfilter driver with pointer to structure */

	return 0;

/* netfilter_exit: cleanup function */
static void
__exit netfilter_exit(void)

	/* unregister the driver */

/* explicit module definitions */


Any help greatly appreciated.

Thanks and regards,
Srinivas G

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