[Info-vax] mmap on VMS - (was: Anyone interested in another public access system)

[John E. Malmberg]

Bob Eager wrote:
> On Sun, 12 Apr 2009 22:13:57 UTC, Michael Kraemer <M.Kraemer at gsi.de> 
> wrote:
> 
>> Bob Koehler schrieb:
>>> In article <grqqh7$ore$03$1 at news.t-online.com>, Michael Kraemer <M.Kraemer at gsi.de> writes:
>>>
>>>> if performance is an issue, on Unix I'd use mmap() services in such cases.
>>>>
>>>
>>>    Thanks you for making my point!  It seems that the lack of current
>>>    emacs ports to systems like VMS is because someone decided to mmap()
>>>    the files and do the record stuff themselves.  Shooting everyone
>>>    else in the foot!
>>>
>> I don't see why this would make your point.
>> mmap() (or equivalent) services should be available
>> on all systems with native support for an MMU,
>> which includes Unix, WNT and possibly also VMS.
> 
> Yes, easy enough in VMS; I've done it many times. RMS $OPEN with FOP=UFO
> in the FAB. Then use $CRMPSC.

mmap() on a program written for for UNIX only works on VMS files that 
are the same in memory as on disk, like stream and binary formats.

Most text files on VMS are variable record format with implied carriage 
control.

So mmap() can not be used to for a partial update of those type of text 
files.

Coming up with a mmap() that can work on all VMS file types in a way 
that Unix programs expect, and have it efficient is not an easy thing to 
do.

-John
wb8tyw at qsl.network
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