Re: definition of terms (was: Re: Adding PCMCIA support to the kernel tree -- developers needed.)

[Vojtech Pavlik <vojtech@suse.cz>]

On Fri, Feb 09, 2001 at 06:03:30PM +0100, Oliver Neukum wrote:

> > > I fear we are being sucked down by semantics.
> >
> > You can't get away from that in design discussions.  Gotta
> > eliminate confusions up front.
> >
> > And this application structure is very important.  You can't
> > design a "system" without knowing the ways people interact
> > with it ... /dev/NNN is no more than one part of a 1970s
> > solution to a simpler system problem than we have today.
> > We can still use it, but it's not a straightjacket to live in.

> 'interface driver' - a kernel space driver that user space can use to talk to 
> a physical devices. There may be more than one interface driver per physical 
> device, or in rare cases, none.
> 
> 'logical driver' - interface the user space agent may set up, which allows 
> the rest of user space to use the services a physical device offers, optional

> logical driver: epson backend of SANE
> interface driver: usbscanner.o

> I introduced the term 'interface driver' because it is needed.

But it's a very problematic one - there is nothing like a driver that
connects directly hardware and userspace. There is always several
drivers inbetween.

In the case of USB scanner:

[hw]--(pci)-->usb-ohci.c--(usb)-->scanner.c--(chardevice)-->[userland]

In many cases there is much more. If there were only direct

[hw]-->xxx.c-->[userland]

drivers, we wouldn't need any hotplug support - kmod and friends would
be enough, because we would then be able to load the modules based on
userland requests. And that is not the case. For USB scanner working, we
need both usb-ohci.c and scanner.c loaded.

So, if you define 'interface driver' as the last driver instance before
a layer (chardevice, netdevice, blockdevice) that interfaces to
userland, then OK. But we need to take the other drivers into our view
as well.

-- 
Vojtech Pavlik
SuSE Labs

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