linux-kernel - CLOCK_MONOTONIC datagram timestamps by the kernel

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Date:	Sun, 25 Feb 2007 22:29:48 +0100
From:	John <linux.kernel@...e.fr>
To:	linux-kernel@...r.kernel.org
CC:	johnstul@...ibm.com, mingo@...e.hu, zippel@...ux-m68k.org,
	tglx@...esys.com, linux.kernel@...e.fr, akpm@...ux-foundation.org
Subject: CLOCK_MONOTONIC datagram timestamps by the kernel

Hello,

It is possible to ask Linux to timestamp incoming datagrams when they
are received, then to retrieve this timestamp with an ioctl command or
a recvmsg call (which would save one round trip to kernel space).

SIOCGSTAMP
     Return a struct timeval with the receive timestamp of the last
packet passed to the user. This is useful for accurate round trip time
measurements. See setitimer(2) for a description of struct timeval.

As far as I understand, this timestamp is given by the CLOCK_REALTIME
clock. I would like to get the timestamp given by a different clock: the
CLOCK_MONOTONIC clock.

In other words, I would like the kernel to do the equivalent of

   struct timespec spec;
   clock_gettime(CLOCK_MONOTONIC, &spec)

for each datagram the system receives, as soon as it is received.

Is there a way to achieve that?

Is there a different ioctl perhaps? (I don't think so.)

Regards.
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