[Info-vax] New filesystem mentioned

[Simon Clubley]

On 2019-05-16, Dave Froble <davef at tsoft-inc.com> wrote:
> On 5/16/2019 10:04 AM, Bob Koehler wrote:
>>
>>     No, DLM is a separate part of the kernel, which is used by and
>>     required by the XQP and such.
>
> Damn, that brings up another question.  Is the DLM part of the kernel? 
> I don't know the details of the implementation, but, I'd at least hope 
> it is not.  That would allow it to be used in any modular type of OS. 

It is a part of the kernel, but only in so far as there is no other place
to put it in the current VMS design. I can't see anything about the VMS
DLM which requires direct access to hardware for example.

It provides services to the rest of the kernel (and to non-kernel
applications). However, I see no reason why the DLM could not just be
another task in a microkernel design (for example).

> And before anyone mentions parts of the kernel might use the DLM, I'd 
> guess that might happen.  Doesn't mean anything used by the kernel is 
> part of the kernel.
>

In a VMS style monolithic design, it's all part of the kernel.

This is because, on VMS, the DLM directly provides services to the rest
of the kernel which means the kernel code needs direct and efficient
access to the DLM.

Think of it less about being part of the kernel and more about whether
the DLM has a clean interface to the rest of the kernel (which would
make it easier to use elsewhere).

Going back to Linux, that's one of the advantages of the Linux module
based architecture. It's all part of the kernel, but there are generally
reasonably clean interfaces between the various parts of the kernel as
a result.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
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