Re: New thoughts about deva/fabrica

[ness]

> > Actually, most of the advantages listed there can be implememted in the
> > original ddf proposal by Peter De Schrijver and Daniel Wagner.
>
>
> I don't think so.  The idea as far as I understood it was to allow device
> drivers to use posix and hurd features.  That is prohibited by the "OS
> independant" approach.
Well, I meant the advantages for users - not for developers :D.
> > Second, while readin' the 
> > mailing list it tourned out for me that there're lots of disadvantages 
> > we have with posix level drivers, and not the smallest one is speed. 
>
>
> Device drivers are not required to use the posix features.  Some drivers, such
> as the USB bus driver, will be used a lot, and every optimisation in them is
> worthwhile.  Such drivers should not use posix features if it slows them down.
> But if I (as a user) want to write a driver for an unsupported device, it
> would be very nice indeed if I'm not required to live with a restricted
> environment.  This is exactly the reason why I don't do so much kernel hacking
> on Linux.  The stuff is annoying to write and annoying to debug.
>
> Of course the hurd is much less restricted by those problems, because many
> things which are drivers in Linux are translators here, but I would very much
> like to also allow core drivers to be "normal" translators.  However, only as
> long as it doesn't hurt performance.  That is, if allowing this causes severe
> performance penalties for drivers which _don't_ make use of it, then it
> shouldn't be done, in my opinion.
That is clear. But you can debug drivers as ordinary progs.
> > Third, if u have a look at "conventional" drivers, there's no or very 
> > less need of libc functions.
>
>
> That's because they're not allowed to be used from there. ;-)  I would add a
> network server to my Linux device drivers for debugging or controlling if I'd
> be allowed by Linux.  But I'm not, so I don't use all the libc calls for
> networking.  I don't have a real idea of what I'd use if everything was
> allowed, but I think it would be quite a lot.
This might be right.
> > And fourth, there's a pragmatic reason: a 
> > microkernel allows to run multiple OS in parallel. And we shouldn't skip 
> > this great advantage. But I don't see a way to marry posix level drivers 
> > and OS independend drivers.
>
> <skip explanation>
>
> I don't agree with you here.  Our first priority should now be to get a
> working system (on L4).  I feel it's hard to contribute to the project at the
> moment because I can't write or port "normal" programs.  I've heard from
> others they're also waiting until the system has some device drivers.  I think
> we really shouldn't delay ourselves even more by trying to add extra features
> which most people will not use.
>
> I think we should get some code written as soon as possible.  Then we can see
> what works.  I feel we should allow posix drivers, because it greatly
> simplifies the task of device driver writers.  For drivers which really need
> it, we can (possibly later) write them without those features.
>
> Perhaps it will later be very hard to make running multiple OSs possible.
> Perhaps a new ddf needs to be written for it.  That may take years.  But if we
> want to allow it now, it may also take years, and as an extra "bonus", it will
> prevent some people from writing drivers for us, because they feel it's too
> restrictive.
Question of point of view. I don't know what is more important.

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-ness-