Re: (Semi-random) thoughts on device tree structure and devfs

[David Young <dyoung%pobox.com@localhost>]

On Thu, Mar 11, 2010 at 10:16:56AM +0900, Masao Uebayashi wrote:
> On Thu, Mar 11, 2010 at 12:13 AM, David Young <dyoung%pobox.com@localhost> 
> wrote:
> OK, you want to match device by ID.  Like:
> 
>         fxp* macaddr xx:xx:xx:xx:xx:xx
> 
> That might make sense.
> 
> What doesn't make sense there is to *fix* device unit number.  Device
> unit number will be no longer used after devfs, because we lookup
> struct device by either topologically or ID.

No device unit number?  You've lost me.  Please fill in the blank,

ifconfig ______ inet 192.168.1.1/24

:-)

> Device probes, configures, and extracts properties from the real
> device.  Just before leaving attach(), it *puts* its ID in a
> well-known place so that device(9) can lookup these IDs later.

Actually, that sounds great to me.  Then we can, as you suggested at
the top of this thread, create the ether(4) pseudo-device that is
analogous to audio(4).  Let us attach a particular ether(4) instance to
an ethernet h/w instance according to the h/w's properties.

Take fxp(4) for an example.  Rename it fxphw(4).  Let it attach an
ether(4) instance at its ether attribute, using an optional 'basename'
attach argument of 'fxp', so that the ether(4) instance knows that it
should take its customary name, fxp0 (or whatever).

I think that an added benefit of breaking things down this way is that
we can attach >1 ether(4) to a single h/w instance, which makes a sense
with those NICs that support >1 unicast address.  Maybe we can attach
vlan(4) to the h/w backend's ether attribute, too.

Another added benefit of breaking things down this way is that we may be
able to get rid of the problematic "network" class in PMF.

You seemed to have in mind attaching at fxp0 an ether0, and attaching at
ether0 a net0.  What is net0's role?

BTW, I have considered previously that splitting the WLAN drivers into
hardware backends and pseudo-device frontends makes a lot of sense as
you consider the possibility to operate more than one 802.11 station on
a single hardware adapter.  It would probably look something like this:

rtwhw0
|
+---net80211arb0
    |
    +---rtw0
    |
    +---rtw1

rtw0 and rtw1 are instances of net80211 state machines.  They command
net80211arb0 to send packets and to pass back received packets meeting
certain criteria ("received on channel y, BSSID x, destinations {p, q,
r}"). net80211arb0 will arbitrate access to the hardware. rtwhw0 will
actually operate the device.

> I wonder if we can assume serial numbers are unique.

We cannot.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933