Re: devices with more than one node

[Greg KH <greg@kroah.com>]

On Tue, Jan 13, 2004 at 08:12:56PM -0500, dougg@torque.net wrote:
> Quoting Greg KH <greg@kroah.com>:
> 
> > On Tue, Jan 13, 2004 at 03:01:47PM -0800, Patrick Mansfield wrote:
> > > Don't forget to let the scsi people know ;-) cc-ing linux-scsi
> > 
> > Ok, here goes:
> > 
> > linux-scsi, DO NOT USE THE cdev sysfs directory.  It will be going away
> > as soon as I get around to writing the patch for it.  Putting the sg
> > symlink in there is not the proper place.
> 
> Greg,
> Is the register_chrdev_region() call which according to
> J. Corbet's documentation allows support for more than 256 
> devices, going away? Or is it simply going to lose its
> sysfs visibility (in the /sys/cdev/major directory)?

Just the sysfs visibility is going to go away.

> > For scsi generic you should create a scsi generic class (scsi_generic?)
> > and create the individual sg devices in that directory (feel free to use
> > the simple_class.c code that is currently in the -mm tree if you want,
> > it makes it much simpler)
> 
> Does any device use the simple_class.c code yet?

I've posted patches that provide the following device support using the
simple_class.c code:
	- tty devices
	- sound devices
	- frame buffer devices
	- input devices
	- memory devices
	- misc devices
	- virtual console devices

All of those patches are in the -mm tree (well the vc device patch is
currently commented out due to some wierd bugs...)

I'll probably be spinning another set of those patches tomorrow, as I've
fixed some race conditions in the simple_class.c code now.

> > > st also needs changes.
> 
> and osst.
> 
> Kai changed the st naming scheme in /sys/cdev/major/st*
> in a way that seems to allow for more than 8 variants
> of each device.

Great.

> > I agree.
> > 
> > > Did anyone figure out how udev should handle the one tape device requiring
> > > multiple minors (for open/close with/without rewind)? It really is a
> > > single device requiring multiple dev entries.
> > 
> > Create multiple class_device items for every tape device and have the
> > device symlink point to the same scsi device.  The simple_class code
> > should make life a lot easier for you.
> > 
> > > For scsi_id support with udev, st needs to support SG_IO, AFAIUI it can
> > > use similiar code as found in sd.c and sr.c.
> > 
> > That's a scsi core issue, not a udev issue :)
> 
> Well, before cdev gets ripped out, following two symlinks
> (i.e. tape -> device -> generic) solves the long standing
> ULD to sg (and vice versa) mapping problem.

But they do not provide a "dev" file, and the hotplug event, which is
what userspace tools like udev require.  They also are the only types of
devices that use the cdev tree :)

If you make a class device, it will provide a symlink that you can use
to point to the device that sg is bound to.

Hope this helps,

greg k-h


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