Re: time stamps of skb packets in NF_HOOKS callbacks

Evgeniy,
Sorry ! ; last sentence in my reply was chopped so here is my message
again with this last sentence (complete this time)

Thnks, I appreciate your (quick) answer;


Following your answer I tried adding a call to net_enable_timestamp() in
a module I wrote which use NF_HOOKS.
This is what is done , for example, in ipq_rcv_skb(struct sk_buff *skb)
in linux-2.6.14 in net/ipv4/netfilter/ip_queue.c.

After doing so I get timestamps which are not 0.

what I wonder now is :
1) does this have ANY performance implication (when dealing with a
high  network  load which can get to 50,000 packets per second?
2) It does work as I said, but I want to be cautios: Am I permitted to
add this method ? are  there any  implications for adding this method
which can create troubles ?
I must say that I am NOT changing anywhere the timestamp; it's only
for statistics.

Regards,
John




On 8/17/06, Evgeniy Polyakov [off-list ref] wrote:

On Thu, Aug 17, 2006 at 05:37:15PM +0300, John Que (qwejohn@gmail.com) wrote:

quoted

Hello,
I am using NF_HOOKS (a "PRE_ROUTING" hook).
When I try to print the time stamps (sec and usec) of skb packets
which I recieve
in the hook callback I get 0. Other skb fileds are correct.
According to my understanding, the time stamp should be updated
when the packet is received. Isn't it so ? Any idea why am I getting
"0" for tstamp fields (tstamp is a field in sk_buff and is  an intance
of skb_timeval).

Timestamps are disabled by default, if you have sockets which enable
SO_TIMESTAMP or netfilter queue target and other agents which can enable
it, you will see updated values in skb->tstamp.

--
        Evgeniy Polyakov