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

[Arne Vajhøj]

On 12/1/2020 8:15 AM, geze... at rlgsc.com wrote:
> 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.

> 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.

His point is that there should not be any breaking
changes to API's only pure extensions.

And I think VMS has followed that model.

When going to 64 bit we got a bunch of _64 system
services.

And even though SYS$QIO(W) has not changed much then it did
get supplemented by SYS$IO_PERFORM(W).

Arne