[Info-vax] What would be involved in moving RMS into kernel mode ?

[Dave Froble]

On 5/4/2023 10:24 AM, Hein RMS van den Heuvel wrote:
> On Tuesday, May 2, 2023 at 9:24:03 AM UTC-4, Simon Clubley wrote:
>> If the emulated executive mode is a major reason for the kernel overheads
>> we are seeing on x86-64 VMS, what would be involved in moving RMS from
>> executive mode directly into kernel mode ?
>
> Nah, have a link time option to run RMS in user mode! I'm mostly serious.
> Moving it to kernel mode you still need to probe the RABs, FABs, XABs and anything those point to.
> The protection exec or kernel mode offers is minimal. It makes sure that broken user mode doesn't stomp on data block buffers and corrupts the underlying file impacting downstream usage of those files.  Possibly worse, in user mode buggy programs could impact other, shared, users of those files, specially when global buffers are involved.
> Well tough luck, write better program, test them better!
> Exec mode RMS might help the testing but when is the last time your programs accidently tried to touch an rms buffer and got an accvio?
> It (exec or kernel) mode only protects against accidental data corruption (bugs).
> It doesn't protect against malicious corruption as anyone with write access can overwrite data.
> Regular file protection handles that. Only allow trusted users, or subsystems holding the right identifier, access to critical files.
> Admittedly RMS does use CMKRNL for some odd things like borrowing/stealing ENQLM to get out of a tight spot, but in general user mode could be just fine.
>
> fwiw ... back in the day (30 years) ago, while in VMS Engineering I had access to usermode RMS for debugging purposes. It did exists at the time with minimal restrictions. It was rarely - if ever - used. Mostly we worked of crashdumps and 'live' ANAL/SYSTEM to look at the data structures to debug RMS.
>
> Hein.
>

I have to agree with Hein on this subject.  I don't see what inner modes do for 
accessing and updating data.

I've got an old database product, similar in some ways to RMS, that runs in user 
mode.  The only inner modes used are for system wide locks, so that required 
privs are not assigned to the users.  Works just fine.

-- 
David Froble                       Tel: 724-529-0450
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