Re: devices with more than one node

[Mike Anderson <andmike@us.ibm.com>]

Greg KH [greg@kroah.com] wrote:
> > To test it I modded scsi_debug to fake OnStream tape
> > drives and ran a 2.6.1-mm2 kernel. The attached
> > output of "cd /sys/class; tree scsi* osst" is instructive.
> > Two peculiar entries are:
> >     scsi_generic/sg0/driver -> ../../../bus/scsi/drivers/osst
> >     scsi_generic/sg1/driver -> ../../../bus/scsi/drivers/osst
> > 
> > This symlink only appears if the osst driver is loaded
> > _before_ the sg driver! It is also left dangling by
> > "rmmod osst". It seems that sysfs is still not happy
> > with multiple drivers controlling the one device.
> 
> The driver model does not allow this, and probably will not in the
> future.
> 
> Just keep sg as a "class", like this patch does.  That should fix your
> issues, right?
> 

Greg a clarification check. There is a scsi_device class already that sg
registers an interface with. The interface of scsi_device class is used
to add / remove the scsi_generic simple class devices and this is ok to
keep doing (not that there is another easy way to do this since sg does not
bind).

> > The scsi subsystem solution to this is to relegate sg to be a sysfs
> > "non" driver. Hence sg has no entry under
> > /sys/bus/scsi/drivers and thus no obvious place to
> > put its driver parameters. Sg driver parameters could be
> > placed in the /sys/class/scsi_generic directory (with
> > class_create_file() ). Suggestions?
> 
> That's a good place for them.  Unfortunatly the changes I made to the
> class_simple.c code does not provide you the ability to do this.  If you
> want to do this (and I think it is a good idea) you will have to write
> your own class code (like the usb_host class code).
> 

Another option that should work is that sg could register as a
scsi_driver and use bus_match to ensure it never binds. The only
difference between the other upper level drivers would be the links to
the devices in bus/scsi/driver/sg would not exist like other upper level
drivers. You would have a place though for driver attributes.

-andmike
--
Michael Anderson
andmike@us.ibm.com