[Info-vax] Greg Kroah-Hartman on backwards compatibility

[geze...@rlgsc.com]

On Monday, November 30, 2020 at 10:24:23 AM UTC-5, Arne Vajhøj wrote:
> https://thenewstack.io/greg-kroah-hartman-lessons-for-developers-from-20-years-of-linux-kernel-work 
> 
> He talks about Linux, but I think we could do s/Linux/VMS/w 
> without anyone noticing. 
> 
> Arne
Arne,

I am not sure about the systemd comments, but I will beg to differ on the API comments.

It most definitely is possible to architect and implement APIs that endure for decades, without change. One must specify what must be specified, and leave undefined what is not necessary. If semantics are preserved, one of the most common errors is variable range (16 vs. 32 vs. 64 bit), but variable range issues, while challenging, are less disruptive than semantic changes. OpenVMS QIO is an example of an API which has been semantically unchanged for close to 50 years, originating on RSX-11 members in the early 1970s.

I spoke about this years ago at several conferences in a session entitled "Forethought: The Unspoken Foundation of Evolution", the slides can be found at: http://www.rlgsc.com/iasa/nyc/2009/forethought-unspoken-foundation.html. I also spoke several times specifically on API architecture.

- Bob Gezelter, http://www.rlgsc.com