CLOCK_MONOTONIC datagram timestamps by the kernel

[John <linux.kernel@free.fr>]

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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