Proposal - drop the GPSD JSON driver

[Hal Murray]

>> 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?

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.

I just checked ntpd/refclock_shm.c
It's got int's, no longs.  So does gpsd.
We should make things explicit for the great SHM cleanup.
It's also got time_t.   That will break the 32/64 bit combination on Fedora.  It's 4 bytes on 32 bit systems and 8 bytes on 64 bit systems.

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>> 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)



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