netdev - Re: Problem with frame time stamping

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Message-ID: <4739A2FB.8030800@cosmosbay.com>
Date:	Tue, 13 Nov 2007 14:13:31 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Antoine Zen-Ruffinen <antoine.zen@...il.com>
Cc:	netdev@...r.kernel.org, linux-net@...r.kernel.org,
	netfilter-devel@...r.kernel.org, patrik.arlos@....se
Subject: Re: Problem with frame time stamping

Antoine Zen-Ruffinen a écrit :
> THIS is what I did at the beginning. But is seem me to be some thing
> wrong. So I put a static value in skb->tstamp  instead of
> ktime_get_real() for debug purpose. And I was still becoming the
> amount of second, microsecond since 1970. We are back to my initial
> mail ! The value of skb->tsamp doesn't seems to be returned by
> ioctl().
>   
OK Antoine.

Yes, 'struct timeval' is as you discovered, ie relative to *something*, 
a given event in the past. (in your case, CLOCK_REALTIME Epoch : January 
1th 1970)

It is even documented (man gettimeofday)

DESCRIPTION
       The  gettimeofday() function shall obtain the current time, 
expressed as seconds and microseconds since the Epoch, and store it in the
       timeval structure pointed to by tp.

For timespec STAMPNS, see clock_gettime() description.

clock_gettime(CLOCK_REALTIME, &ts);

If in your driver you stick in tstamp.tv64 a value like 0x00010002, then 
the result of ioctl(SIOCGSTAMP) will be :
tv.tv_sec = 0   (so yes, January 1th 1970)
tv.tv_usec = 65   (because 0x10002/1000 = 65)

Not counting the fact that .tv64 should not be directly set, unless for 
0 value, because it is not portable.





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