Proposal - drop the GPSD JSON driver

Gary E. Miller gem at
Thu Oct 20 18:40:00 UTC 2016

Yo Hal!

On Thu, 20 Oct 2016 03:38:00 -0700
Hal Murray <hmurray at> wrote:

> gem at said:
> > Not a POSIX sharde memory one.   
> What do you mean by POSIX in this context?  How would I recognize one
> if I was looking at it?

We are talking about the shared memory functions that POSIX defines.

read this: man 7 shm_orverview

> > Say what?  The existing protocol has serious problems.  
> What sort of problems are there with the current one?

Do we really need to go over this yet again?  These have been covered
for years.

First, the structure needs to be polled, sometimes leading to long
delayed and even missed samples.

Second, a big one, the C structure is of loosely defined size and shape.
Even on the same host you need to use the same compiler and word length
for client and server.  For example, you can't compile the client as 32
bit and the server as 64-bit.

Third, you pretty much need to reboot the server when you change the struct
size as deleting the old SHM segment while running is problematic.

Fourth, teaching people to debug with ipcs is a PITA.

Fifth, security is hopeless.  Client and server both need to run as
root to be somewhat safe and only 2 SHM slots can do that.  After that
the SHMs are wide open to anyone on the server to mess with.

Sixth, so many of these problems are so hard to grasp that people
get amnesia about them after on eday.

Seventh...  well.  I could go on but I need more espresso, and the following
should be more than enough to show the current SHM needs killing off.
Sadly that will take a decade, after the next good solution is

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