[Info-vax] Reloading device drivers on x86-64 VMS

[David Froble]

Craig A. Berry wrote:
> On 3/8/15 8:38 PM, David Froble wrote:
> 
>> If you want to install a new version of a sharable image, if it's
>> compatible with the old version, what does it matter how long before the
>> old version isn't used?  If it isn't compatible, I think you got more to
>> worry about than replacing a sharable image.
> 
> I never said anything about loading a new version. The word was "unload"
> and in a subsequent post I referenced "a dlclose() or equivalent that
> actually frees up resources," which, despite the reference provided,
> seems not to have gotten the point across.
> 
> Let me try again with an example. A modern web framework might have some
> dozens of modules or classes or extensions or plug-ins or assemblies or
> whatever the loadable pieces are called in your language of choice, and
> each might involve loading one or two or ten shareable images (or more,
> given the long dependency chains). A web server process might load up
> one set of these things to satisfy one request, but then need to load an
> entirely different set to satisfy the next request within the same
> process and main image activation, so you end up with all of the
> resources required by both sets allocated at the same time. Under some
> (but not all) circumstances, it might be desirable to be able to unload
> one set before loading another, basically undoing everything that was
> done by LIB$FIND_IMAGE_SYMBOL.
> 
> Which, as hb said, the VMS image activator cannot do. Which I knew,
> which is why I said it might be a nice feature to add, given that other
> OS's, such as Linux, already have it (the latter of which I didn't say
> previously, but seemed obvious in context).
> 

Yes, I understood what you were saying, and I think the capability 
should exist, if possible.

If it was pageable memory, I normally wouldn't get too excited, but some 
things may take up the non-paged pool resources, and then you can get a 
problem quickly.

That said, it's not something I think I'd ever run into, but one thing 
I'm aware of, lots of people use VMS, and some of them do things I'd 
never think of.  So, just because I would not use something doesn't mean 
it isn't perhaps vital to someone else.

What I'm guessing is that the design of VMS is a bit dated, and HP 
didn't do much if anything to keep up with advances in OS technology. 
So, in addition to doing some catch up, there might be some decent 
things to show the way, making the job much easier.  One can hope.