Re: APIs and compatibility

[Jonathan S. Shapiro]

On Sun, 2008-08-31 at 11:55 +0200, Neal H. Walfield wrote:
> At Sat, 30 Aug 2008 14:02:40 -0400,
> Jonathan S. Shapiro wrote:
> > It strikes me that rebuilding a very large number of drivers as a
> > precondition to success is probably not a good recipe.
> > 
> > Is there any reason why the linux driver framework cannot be adopted
> > directly by l4-ng?  I do understand that user-supplied drivers are
> > desirable, and I think that remains possible in all of the practical
> > use-cases that have come up here.
> 
> Although custom drivers offer the best potenial quality, writing new
> drivers for all hardware is impractical.  So there must be some reuse.
> However, some reuse does not imply that all drivers must be reused.
> That is, very common hardware or essential hardware can be provided by
> native drivers and the rest by way of reuse.

I agree with all of these points. But this does imply that certain
*interfaces* from Linux become mandatory: those that in SVR4 would have
been called the "Driver Kernel Interface". This is ad hoc in Linux, but
it exists.

> This hair can be avoided by reusing Linux in its entirety.  In this
> case, Linux is run on a VMM and the new operating system makes calls
> to the Linux driver instance.  Two examples of this are Afterburner or
> Xen.  Both use a paravirtualized Linux instance.

But if this is done, what is the advantage of having a microkernel at
all?


shap