Re: The Ravenscar profile and capabilities paradigm

[Doctor Who <doc@tardis.org>]

On Tue, 12 Oct 2021 16:43:07 +0100, "Luke A. Guest"
<laguest@archeia.com> wrote:

>On 12/10/2021 16:33, Shark8 wrote:
>> On Tuesday, October 12, 2021 at 9:04:09 AM UTC-6, Luke A. Guest wrote:
>>> On 12/10/2021 16:01, Shark8 wrote:
>>>> On Monday, October 11, 2021 at 1:24:48 PM UTC-6, Doctor Who wrote:
>>>>> On Mon, 11 Oct 2021 16:32:13 +0100, Simon Wright wrote:
>>>>>> Doctor Who writes:
>>>>>>
>>>>>>> someone knows how to introduce the capabilities paradigm in Ada,
>>>>>>> specifically for programs written using the Ravenscar profile ?
>>>>>>
>>>> Type Capability is ( Read, Copy, Whatever );
>>> There can be a capabiity for literally anything, even ownership and can
>>> be different depending on object/os service.
>>>
>>> I'd say a tagged type is better than an enum.
>> Possibly.
>> But there's no reason to complicate the general idea in example-form: even if it's a tagged type you're going to want the capability-instance to be limited-private; the implementation of the "permissions" component being a Boolean-array or a vector of Capability'Class [most obviously having Capability be an abstract tagged null record] is mostly irrelevant for that demonstration. (And using a vector of tagged-type instead of the array would have bogged the example down with importing and instantiating the Vector container and setting up multiple non-abstract Capability-descendants, cluttering the point of the example.)
>> 
>
>Capabilities allow granting and revoking of access, iirc, the kernel has 
>access to all, the kernel then grants access to certain processes, i.e. 
>memory server, filesystem server, etc. each of those processes can 
>further grant and revoke caps.
>

thank you all for the help, I hope this discussion goes far.
the most useful approach is the microkernel, where access to, and
operation of, each service is mediated by capabilities.

I would go so far to define and implement a capability-based
microkernel written in Ada using the Ravenscar profile.