DragonFly kernel List (threaded) for 2003-10
Re: Microkernel architecture?
On Thu, 02 Oct 2003 21:49:20 -0500, Pedro Giffuni wrote:
> This is off topic, (but just for reference and because there is not
> technical-chat list ...)
> when you mentioned you wanted a userland VFS API, I recalled someone already did
> that: in fact, they turned everything into libraries and made the kernel very
> small... they called it an Exokernel:
I have played with Exokernel long time ago. It was a very fast kernel, but
little unstable that time when I tried.
> They invented softupdates, BTW :).
> Matthew Dillon wrote:
>> :I have a question: since so many of this new OS's features are commonly
>> :found in microkernel-based systems, why isn't DragonFly being planned as
>> :a microkernel design instead of a monolithic kernel with a few
>> :microkernel tricks? Or is DragonFly microkernel-based?
>> 'microkernel' is a badly misused term. While it is theoretically
>> possible to build a microkernel, actually making it do useful things
>> requires a level of integration that is fairly difficult to achieve
>> in a microkernel design.
>> What we can do is move the bottomost layers, primarily device drivers,
>> the networking layer, and filesystems, towards a microkernel-like
>> message-passing design. The KLD mechanism is capable of dynamic loading
>> this layer. Even so there are still a large number of heavily
>> integrated structures which are simply passed by reference, such as
>> 'struct ucred'. There are dozens such structures and it is the
>> existance of these structures that makes it unlikely that the
>> microkernel aspects of the system could be extended much beyond what
>> we have already contemplated for DragonFly.
>> Nor would I particularly want to try. I see no advantage at all in
>> trying to convert the system wholely to a microkernel design, other then
>> to slow it down and make the source code harder to understand :-)
>> Matthew Dillon
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