On Tue, Feb 07, 2017 at 12:37:15PM -0800, sdncurious wrote:

On Tue, Feb 7, 2017 at 6:01 AM, Miroslav Lichvar [off-list ref] wrote:

quoted

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.

-- 
Miroslav Lichvar