device module auto loading fix

[Adam Hamsik <haaaad%gmail.com@localhost>]

Hi folks,

I tried to look at issue reported by nicholas (kernel panic during cd  
boot).
And I found that there areat least two bugs which lead to this panic.

1) [bc]dev_open

 In spec_open [1] we try to open device and when open function fails  
with
 ENXIO which means that device was not found in a list, we try to  
autoload
 it. Problem is that wecan get ENXIO even when driver is already  
present in
 kernel. This is issue reported by nicholas. Attached diff adds new  
only in
 kernel errno ENODEVSW which is reported by [bc]dev_open routine when
 [bc]dev_lookup function fails.

 To be clear here I do not need to add new errno, what I need is  
distinguish
 between error in bdev_lookup and device open routine.

2) scsipi/cd.c
 During testing, I was not able to boot install cd even with my  
patch. I have
 found that version 1.284 of cd.c (was not pulled to -5) file  
introduces some
 bug which makes cdopen return ENXIO during boot of install cd.  
Reverting to
 1.283 version fixes problem for me and I can boot -current install  
cd again.

Do you have any suggestions ? Is it ok to commit attached patch ?

 [1] http://opengrok.netbsd.org/source/xref/sys/miscfs/specfs/spec_vnops.c#451

Attachment: specfs.diff
Description: Binary data

Regards

Adam.