Re: Linux IP stack change to obtain TTL min/max/avg

[mpk_india <mpk_india@yahoo.com>]

Hello Sam,

Can you elaborate more on how I can fetch these TTL min/max/avg values using
netdev?

Thanks

Mpk 

Sam Ravnborg wrote:
> 
> netdev is a much better place for this - added.
> 
> 	Sam
> 
> On Wed, Dec 31, 2008 at 03:20:53AM -0800, mpk_india wrote:
>> 
>> Hello All,
>> 
>> I am trying to modify the linux ip stack to get the avg/min/max of the
>> TTL
>> value (in trasport layer) from the received UDP packet. I have modifed
>> the
>> 2.6.28 kernel for this and added new setsockopt flags as IP_RECVTTL_AVG,
>> IP_RECVTLL_MIN, IP_RECVTTL_MAX.
>> 
>> Please see below changes I have made to do this:
>> 
>> 1. Inside "in.h" file Added following macros
>> #define IP_RECVTTL_AVG	20
>> #define IP_RECVTTL_MIN	21
>> #define IP_RECVTTL_MAX	22
>> 
>> 2. Inside "inet_sock.h" in struct inet_sock {
>> added 3 variables
>> __s16	 uc_ttl_avg;
>> __s16	 uc_ttl_min;
>> __s16	 uc_ttl_max;
>> 
>> 3. In ipv4/udp.c added following peice of code
>> sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
>> if (sk != NULL) {
>> 
>> #if 1	// Changes to get TTL stats..Start
>> struct iphdr *iph;
>> struct inet_sock *inet;
>> inet = inet_sk(sk);
>> iph = ip_hdr(skb);
>> inet->uc_ttl_avg = (iph->ttl + inet->uc_ttl_avg)>>1;
>> if (inet->uc_ttl_max < iph->ttl)
>> inet->uc_ttl_max = iph->ttl;
>> if (inet->uc_ttl_min > iph->ttl)
>> inet->uc_ttl_min = iph->ttl;
>> #endif	// Changes to get TTL stats..Start
>> 
>> int ret = udp_queue_rcv_skb(sk, skb);
>> sock_put(sk);
>> 
>> 4. Changes inside "ip_sockglue.c" file
>> 
>> static void ip_cmsg_recv_ttl_avg(struct msghdr *msg, struct sk_buff *skb)
>> {
>> struct inet_sock *inet = inet_sk(skb->sk);
>> int ttl = inet->uc_ttl_avg;
>> printk(KERN_DEBUG "***<recv ttl avg () is called -- value = %d***\n",
>> ttl);
>> put_cmsg(msg, SOL_IP, IP_TTL, sizeof(int), &ttl);
>> }
>> 
>> static void ip_cmsg_recv_ttl_max(struct msghdr *msg, struct sk_buff *skb)
>> {
>> struct inet_sock *inet = inet_sk(skb->sk);
>> int ttl = inet->uc_ttl_max;
>> printk(KERN_DEBUG "***<recv ttl max () is called -- value = %d***\n",
>> ttl);
>> put_cmsg(msg, SOL_IP, IP_TTL, sizeof(int), &ttl);
>> }
>> 
>> static void ip_cmsg_recv_ttl_min(struct msghdr *msg, struct sk_buff *skb)
>> {
>> struct inet_sock *inet = inet_sk(skb->sk);
>> int ttl = inet->uc_ttl_min;
>> printk(KERN_DEBUG "***<recv ttl min () is called -- value = %d***\n",
>> ttl);
>> put_cmsg(msg, SOL_IP, IP_TTL, sizeof(int), &ttl);
>> }
>> 
>> void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb)
>> {
>> .
>> .
>> .
>> .
>> #if 1	// Changes to get TTL stats..Start
>> if (flags & 1)
>> ip_cmsg_recv_ttl_avg(msg, skb);
>> if ((flags>>=1) == 0)
>> return;
>> if (flags & 1)
>> ip_cmsg_recv_ttl_min(msg, skb);
>> if ((flags>>=1) == 0)
>> return;
>> if (flags & 1)
>> ip_cmsg_recv_ttl_max(msg, skb);
>> #endif	// Changes to get TTL stats..Start
>> 
>> }
>> 
>> inside do_ip_setsockopt() added following code
>> 
>> #if 1	// Changes to get TTL stats..Start
>> case IP_RECVTTL_AVG:
>> if (val)
>> inet->cmsg_flags |= IP_CMSG_TTL_AVG;
>> else
>> inet->cmsg_flags &= ~IP_CMSG_TTL_AVG;
>> break;
>> case IP_RECVTTL_MIN:
>> if (val)
>> inet->cmsg_flags |= IP_CMSG_TTL_MIN;
>> else
>> inet->cmsg_flags &= ~IP_CMSG_TTL_MIN;
>> break;
>> case IP_RECVTTL_MAX:
>> if (val)
>> inet->cmsg_flags |= IP_CMSG_TTL_MAX;
>> else
>> inet->cmsg_flags &= ~IP_CMSG_TTL_MAX;
>> break;
>> #endif	// Changes to get TTL stats..End
>> 
>> =================================================================
>> 
>> I have compiled this and written the udp client server to test this. 
>> 
>> 
>> In my client application i am sending 64 packets with some dummy message.
>> In
>> server I have used the recvmsg() and setsockopt() to test these changes
>> as
>> below:
>> 
>> setsockopt(serverfd, IPPROTO_IP, IP_OPTIONS, NULL, 0);
>> if (setsockopt (serverfd,IPPROTO_IP, IP_RECVTTL_AVG, &ttl,ttlSize)<0) {
>> 
>> printf ("Error occured in setsockopt\n");
>> exit(1);
>> }
>> 
>> now if i do the recvmsg 64 times after recvfrom in my server code it
>> gives
>> me proper ttl avg values.. but i do not want to seek this values for
>> every
>> packet i receive.. i want them once for all sent 64 udp packets.. the
>> same
>> recvmsg fails if i doit single recvmsg after 64 received packets..
>> 
>> 
>> Can anyone tell about what i am doing wrong in the present scenario?
>> 
>> Thanks in advance
>> mpk
>> -- 
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>> 
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