giffunip at asme.org
Thu Oct 2 19:49:20 PDT 2003
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:
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
> <dillon at xxxxxxxxxxxxx>
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