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Date:	Mon, 12 Nov 2007 17:47:59 +0100
From:	Eric Dumazet <>
To:	"Antoine Zen-Ruffinen" <>
Subject: Re: Problem with frame time stamping

On Mon, 12 Nov 2007 16:42:34 +0100
"Antoine Zen-Ruffinen" <> 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);a=commit;h=b7aa0bf70c4afb9e38be25f5c0922498d0f8684c;a=commit;h=ae40eb1ef30ab4120bd3c8b7e3da99ee53d27a23;a=commit;h=92f37fd2ee805aa77925c1e64fd56088b46094fc

No need to modify a network driver :)

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