Proposal - drop the GPSD JSON driver

Gary E. Miller gem at
Sun Oct 23 01:08:27 UTC 2016

Yo Hal!

On Sat, 22 Oct 2016 03:15:01 -0700
Hal Murray <hmurray at> wrote:

> >> Word-length mismatch between two programs built under the same OS
> >> never happens, or close enough to never that I don't care.  
> > Uh, no.  remember when intel OS went from 32 bit to 64-bit?  It was
> > a huge issue with ntpd.  RasPi is about to have the same
> > problems.   
> What sort of problem do you expect?

Uh, the one I described in the previous email.  Binary C structures
will not match.  Pain ensues, just like last time.

> I'd expect troubles if you tried to run a 32 bit gpsd or 32 bit ntpd
> on a 64 bit system (using 32 bit libraries) while the other one was
> 64 bit and the shared struct used int or long rather than int32_t and
> friends.

Ah, so we agree, yes, those configurations will be problematic.  We
live through that in the intel 32 -> 64 bit treansition, we are about to
live through it again on the ARM.

> I just checked ntpd/refclock_shm.c

Yeah, ugly, ugly, ugly.

> >> As Hal points out, if you version-number the struct properly you
> >> can add fields at the end ad libitum.  
> > IFF you do it right, AND chose a transport that can handle varying
> > lengths. Traditional SHM can not do that.  The current NTP SHM can
> > not do that.   
> The current SHM setup was extended to support nanoseconds without
> breaking old code.  (and it doesn't even have a version number slot)

Yeah, but a ton if extensions not done because it would break old code.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at  Tel:+1 541 382 8588
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