Re: Problem with frame time stamping

From: Eric Dumazet
Date: Mon Nov 12 2007 - 12:11:59 EST


On Mon, 12 Nov 2007 16:42:34 +0100
"Antoine Zen-Ruffinen" <antoine.zen@xxxxxxxxx> wrote:

> Dear all,
>
> I'm writing a network analyzer software using Linux and I need a VERY
> precise frame time stamping. Therefor I am planing to add my own time
> stamping algorithm on a modified network driver. For test purpose I
> did so :
>
> skb->tstamp.tv64 = 0x00010002;
> netif_rx(skb);
>
> On the user side, I ask for the timestamp that way :
>
> ...
> sock = socket(AF_PACKET, SOCK_RAW, type);
> ...
> //bind this socket with the interface using my modified driver.
> ...
> recvByteCount = recv(sock, buffer, 1514, 0);
> ioctl(sock, SIOCGSTAMP, &timeStamp);
>
> I was surprised to see that the var timeStamp was still holding a
> count of second since year 1970.
>
> Investigating a bit into the kernel code, I found that ioctl(sock,
> SIOCGSTAMP, ...) was giving just the current kernel time using
> ktime_get_real().
>
> Are my investigation wrong ?
> Is that a bug in kernel code ?
> Is there an other way to access skb.tstamp from user side ?
>
> Thank's to any one that can help me !

If your kernel is recent enough, you can already get nanosecond precision from skb tstamp, using SIOCGSTAMPNS ioctl or SO_TIMESTAMPNS / SCM_TIMESTAMPNS

(changes where done in March/April this year)

http://git2.kernel.org/?p=linux/kernel/git/davem/net-2.6.git;a=commit;h=b7aa0bf70c4afb9e38be25f5c0922498d0f8684c

http://git2.kernel.org/?p=linux/kernel/git/davem/net-2.6.git;a=commit;h=ae40eb1ef30ab4120bd3c8b7e3da99ee53d27a23

http://git2.kernel.org/?p=linux/kernel/git/davem/net-2.6.git;a=commit;h=92f37fd2ee805aa77925c1e64fd56088b46094fc


No need to modify a network driver :)


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