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

[David Jones]

On Thursday, November 4, 2021 at 9:23:38 AM UTC-4, Arne Vajhøj wrote:
> On 11/4/2021 12:54 AM, David Jones wrote: 
> > Most of PTD$ code runs in kernel mode with some at elevated IPL.
> Very interesting. 
> 
> So it is not a traditional call stack: 
> 

PTD$SERVICES_SHR.EXE is installed as a protected shareable image, the
functions it export will on entry CHMK in order to process the request
in kernel mode via that image's change mode dispatcher. PTD$READW and
PTD$WRITEW invoke CHMK with the code for the corresponding asynch.
function and then call EXE$SYNCH (same way SYS$QIOW works).

> Sounds like somebody did not like SYS$QIO(W). 

Considering how slow the VAX was and that terminal I/O was often many 
many small transfers, that kind of micro-optimization was probably worth
while.