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Message-ID: <CAHoNx58XJ3bcPNaJTwvDVfhetwqhU89G_xuvyfVqZ2hp7rcadg@mail.gmail.com>
Date: Wed, 8 Feb 2017 15:34:52 -0800
From: sdncurious <sdncurious@...il.com>
To: Miroslav Lichvar <mlichvar@...hat.com>
Cc: netdev <netdev@...r.kernel.org>,
Richard Cochran <richardcochran@...il.com>,
Jiri Benc <jbenc@...hat.com>,
"Keller, Jacob E" <jacob.e.keller@...el.com>,
Denny Page <dennypage@...com>,
Willem de Bruijn <willemb@...gle.com>
Subject: Re: Extending socket timestamping API for NTP
On Wed, Feb 8, 2017 at 2:26 AM, Miroslav Lichvar <mlichvar@...hat.com> wrote:
> On Tue, Feb 07, 2017 at 12:37:15PM -0800, sdncurious wrote:
>> On Tue, Feb 7, 2017 at 6:01 AM, Miroslav Lichvar <mlichvar@...hat.com> wrote:
>> > 6) new SO_TIMESTAMPING option to get PHC index with HW timestamps
>> >
>> > With bridges, bonding and other things it's difficult to determine
>> > which PHC timestamped the packet. It would be very useful if the
>> > PHC index was provided with each HW timestamp.
>> >
>> > I'm not sure what would be the best place to put it. I guess the
>> > second timespec in scm_timestamping could be reused for this, but
>> > that sounds like a gross hack. Do we need to define a new struct?
>>
>> What is the use case for this. even if the delay though the PHY's how
>> would that be compensated ?
>
> The idea was that applications like NTP servers and clients wouldn't
> have to care about interfaces and how they map together with addresses
> to PHCs over time. Currently, I use the interface index from
> IP_PKTINFO to get the PHC, but that doesn't work with bridges and
> other virtual interfaces. Another possibility would be an option to
> modify the behavior of IP_PKTINFO to save the index of the real
> interface. I'm not sure how would that compare in difficulty to
> extending SCM_TIMESTAMPING with PHC index.
Why not just return the digest that is in the message ?
Though I am not sure if the least 32 bits will result in too many collisions.
RMS
>
> --
> Miroslav Lichvar
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