Microkernel architecture?

Pedro Giffuni 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:

> :Hi,
> :
> :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 :-)
>                                         -Matt
>                                         Matthew Dillon
>                                         <dillon at xxxxxxxxxxxxx>

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