Question

I have made a module which is transmitting but I don’t know whether the packet which I am transmitting is a ping packet or not. Code is shown below:

 icmp.type = 8;
 icmp.code = 0;
 icmp.un.echo.sequence = i;
 ip4.protocol = 1; //for icmp protocol
 ip4.frag_off = 0;
 ip4.daddr = in_aton(procfs_buffer);
 ip4.saddr = in_aton(ifr->ifr_addr.sa_data);

 len = sizeof(data);

 skb = dev_alloc_skb(1500);
 skb->dev = __dev_get_by_name(&init_net,"wlan0");
 skb_reserve(skb,NET_IP_ALIGN); // header of 2 bytes; increments tail and 
                                // data pointer
 skb->data = skb_put(skb,sizeof(len)); // increments all pointer or adds data
 memcpy(data,skb->data,len);

 skb->transport_header =skb_push(skb,sizeof(icmp));
 memset(skb->transport_header,0,sizeof(struct icmphdr));
 memcpy(skb->transport_header,&icmp,sizeof(struct icmphdr));

 skb->network_header=skb_push(skb,sizeof(ip4));
 memset(skb->network_header,0,sizeof(struct iphdr));
 memcpy(skb->network_header,&ip4,sizeof(struct iphdr));

 // printk("i::%d\n",i);
 // skb->mac_header = skb_push(skb,6*sizeof(0xFF));
 // memset(skb->mac_header,0xFF,6*sizeof(0xFF));
 dev_queue_xmit(skb);
 kfree(skb);

How can I know that it is a ping packet which I am creating and transmitting? Further I want to receieve the ping packet in response to my ping packet which I have transmitted. I would like to use napi but wont mind any other suggestions.

please read a topic : reception napi mode here i could nt understand what to do from the link above…..

Answer 1

a ping packet is simply icmp packet with code 8, with timestamp in its data
icmp echo reply (ping reply) just copies the data from the icmp echo request and sends it back, this way ping can tell you how much time it took for the round trip (now – prev’ sended time)

i am not very familiar with the linux kernel, but be sure to calculate the correct ip and icmp checksums

also for receiving, it might be better to use netfilter