[ntp:questions] new driver development

unruh unruh at wormhole.physics.ubc.ca
Thu Mar 17 20:34:48 UTC 2011

On 2011-03-17, Rob <nomail at example.com> wrote:
> Harlan Stenn <stenn at ntp.org> wrote:
>> Bruce,
>> Please see http://support.ntp.org/bin/view/Dev/RefclockShmV2 and
>> communicate with folks who have been thinking about this (me, Miroslav,
>> Dave Hart, just to name the first 3 folks who come to mind).
>> Making notes on either the above wiki topic or on a separate sub-topic
>> might be even better, as that way other folks can easily see what's
>> going on.
>> I'm curious if we can support both POSIX and SVID SHM from the same
>> codebase, and use a flag bit or a mode to select which one is used.
> IMHO it HAS to be backward compatible.
> E.g. gpsd uses the existing SHM interface, and while the maintainers
> are probably very willing to change the interface when an improved
> option is available, it is not practical to lock-step the upgrade of
> ntpd beyond a certain version with the upgrade of gpsd.
> So ntpd has to support the existing SHM interface for a while, and
> there has to be a mechanism to detect if a newer interface is available.

I suspect what he had in mind was to make an entirely new driver, with
a new number, which was the posix shm driver, and hope that eventually
the old one would decay from lack of use. (His statement that his new
driver would not support non-posix shm was my hint.) Of course that leads to driver
proliferation ( do we really want a world where there are 16000 drivers?
Actually more than 255 would be problematic) since drivers are never
dropped ( someone might be using them) as can be seen from some of the
drivers which are in there and which I suspect at most one person in the
world uses. 

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