[Info-vax] C... the only winning move is not to play...

[Hein RMS van den Heuvel]

On Tuesday, February 18, 2014 9:56:43 AM UTC-5, David Froble wrote:
> Johnny Billquist wrote:
>> :
>>  locate mode is possible in RMS on  RSX. And conceptually it's easy to see >> how to do it. Hmm, are the RMS internal buffers mapped read-only from the 
>> application program perhaps?  That would explain why it would be only for
>> reads in VMS... 

> I believe RMS runs in supervisor mode, 
Actually EXEC mode. Same difference.
This was specifically done for more robust file sharing.
You would not want a rogue program to accidentally scribble into an RMS buffer which gets flushed out and picked up as data by an other process.
The rogue program has to at least use a QIO or SYS$WRITE to (consciously) do that :-)
 
> and the RMS buffers are not accessible from user mode.

Correct... UREW

Locate mode can really only be used for un-shared sequential files.
Indexed files (expect RSX PROLOGUE-1) have the primary key moved to the front of the record and may be compressed.

Selecting Locate mode can turn slightly wasteful as far as virtual memory goes as it forces RMS to mix page protection, getting User-Read pages for IO buffers.

fwiw,
Hein