[Info-vax] DECnet Phase IV broken after VSI update

[David Jones]

On Thursday, November 4, 2021 at 8:54:37 PM UTC-4, Lawrence D’Oliveiro wrote:
> On Thursday, November 4, 2021 at 5:54:21 PM UTC+13, osuv... at gmail.com wrote: 
> > Most of PTD$ code runs in kernel mode with some at elevated IPL.
> So does a device driver. Why do the PTD functions have to be a separate layer from the device driver? Particularly a separate, caller-visible layer that breaks the normal driver QIO abstraction?
> > PTD$READ/WRITE queue request packets directly to FTDRIVER, 
> > skipping some of the overhead of $QIO processing.
> Remember, these are terminals we are talking about -- devices geared to the limits of human I/O bandwidth. Any “overheads” associated with I/O processing would be insignificant compared to the time it takes for a human to type input or read output.

That's a PC menatility, VAXes were timesharing systems with many concurrent users. C was a second class
language in the VAX/VMS world, too, so the API wasn't designed to cater the patterns of the C RTL. Threads
didn't exist, your server process handling many PTYs was state driven by ASTs delivered by the terminal
driver.