Disabling net_timestamp() in net/core/dev.c was one of the first things I tried, among with disabling other "get_timestamp"-like functions. But apparently that's not where packes get timestamped.
Nuno's suggestion turned out to be what I was looking for. Packets are actually timestamped in the function tpacket_rcv in net/packet/af_packet.c Thank you all. On Aug 17, 2011, at 2:57 PM, Fabrizio Giordano wrote: > Do you guys know where packets are timestamped in the kernel? > I'm using a 2.6.32-131.4.1.el6.x86_64 kernel I.e., Linux, of somewhat recent vintage. The time stamp would be in the skb->tstamp field for the packet in question. If the adapter doesn't do hardware timestamps, the time stamp would be set in a call to the __net_timestamp() inline function from the skbuff.h header file, at least according to my 2.6.32.4 kernel tree. That's called by net_timestamp() in net/core/dev.c, which is called from netif_rx() or netif_receive_skb(). Those appear to be called from the network adapter driver; they're called to hand incoming packets to the networking stack. In, for example, the ixgb driver, it's called from ixgb_clean_rx_irq(). Executive summary: packets are, in general, timestamped when they're first handed to the networking stack.- This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe. From: Nuno Martins [mailto:[email protected]] Sent: Wednesday, August 17, 2011 3:23 PM To: [email protected] Cc: Fabrizio Giordano Subject: Re: [tcpdump-workers] Where are incoming packets timestamped at kernel level? On Wed, Aug 17, 2011 at 10:57 PM, Fabrizio Giordano <[email protected]<mailto:[email protected]>> wrote: Do you guys know where packets are timestamped in the kernel? I'm using a 2.6.32-131.4.1.el6.x86_64 kernel and I need to find this information. Thank you very much. Hey, I'm not really sure but i think it is in the tpacket_rcv function in af_packet.c [1] that lives in net/packet in the linux source code. If you go near line 770 in that file you will see that is going to happen some timestamping. [1] http://lxr.linux.no/linux+v3.0.3/net/packet/af_packet.c#L669 - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe. -- Nuno Martins - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe.
