[Info-vax] CRTL and RMS vs SSIO

[Lawrence D’Oliveiro]

On Wednesday, October 13, 2021 at 9:54:14 AM UTC+13, Stephen Hoffman wrote:
> The DEC OpenVMS advanced development group did do a prototype of 
> OpenVMS on Mach a ~quarter-century ago. 

Yeah, but Mach is a microkernel, with all the downsides that microkernels have.

> More recently, a similar starting point might be from seL4 or DragonflyBSD. 
> 
> If you're going to invest the effort and swap the kernel, might as well 
> swap the existing kernel for a newer design.

The trouble with the BSDs is that they do not have compatible kernels. So even though there are only a handful of BSD variants, it is difficult to port kernel-level enhancements between them. While there are something like 350 Linux distros and counting, they do share the same common kernel codebase (and nearly all of the userland too, just dressed up differently).

> Downside of any kernel-swappage is that you pretty quickly then own the 
> kernel you're working with; just as soon as you have to start modifying 
> the kernel to better fit OpenVMS and OpenVMS app expectations.

Try to avoid that. Also remember that the VMS apps are legacy apps; you are trying to maintain existing functionality, rather than take them in new directions. Major new development would be better off being Linux/POSIX-native.

> Possible areas where kernel modifications might necessary? Linux memory 
> management is thoroughly two-ring, and OpenVMS expectations are 
> four-ring. Do you drop those areas from OpenVMS, and force app source 
> code changes? 

Where is there app code that cares about this?

> Other considerations awaiting VSI developers: any hypothetical chunks 
> of OpenVMS linked against Linux, seL4, or some of the other kernels 
> necessarily involves working within GPL2, which means VSI must write 
> all of that source code themselves, and must then release it. 

Oracle vs Google notwithstanding, it has long been the position in most of the open-source community that APIs are not copyrightable.