RE: Question about Hot device Identity

["Guo, Min" <min.guo@intel.com>]

Sorry, I make a mistake, I has UHCI built-in but OHCI not,
but my USB controller is OHCI type, so I can not find 
my cdrom in /sys/block.

Here I run the Udev as following procedure.

1. mount -t sysfs sysfs /sys

2. Edit the udev.h file and replace the following variables with values
  that make sense for your system:
        #define SYSFS_ROOT      "/sys"
        #define UDEV_ROOT       "/root/udev/"
        #define DEV_FILE        "/dev"
        #define MKNOD           "/bin/mknod"

3 . Run make to build the project 

4. Point /proc/sys/kernel/hotplug at the location of the udev binary that
  is created. so I change /proc/sys/kernel/hotplug 's content to  /root/udev/udev.is this right?

5. Set DEVPATH to /sys/devices/pci0/0000:00:0f.2/usb1/1-1/1-1:0/host2/2:0:0:0/scd0

	I don't know whether scd0  is right, because there are no scd0 in the path /sys/devices/pci0/0000:00:0f.2/usb1/1-1/1-1:0/host2/2:0:0:0,but I can mount 
	the USB CDROM with /dev/scd0,there is a dev file  in my /sys/block/sr0 directory.

	here is the detailed outputs of usb1.
	#ls /sys/devices/pci0/0000:00:0f.2/usb1/1-1/1-1:0/host2/2:0:0:0
	access_count  block  device_blocked  model  name  online  power  queue_depth  rescan  rev  scsi_level  type  vendor

6. run . ./test to see the result.

	But what things should happen here? in my machine, there are no outputs, I think dbg information should be outputed at least.

Thanks
Guo Min 
The content of this email message solely contains my own personal views,
and not those of my employer.

	
	

-----Original Message-----
From: Kevin P. Fleming [mailto:kpfleming@cox.net]
Sent: Thursday, June 26, 2003 12:10 PM
To: linux-hotplug-devel@lists.sourceforge.net
Subject: Re: Question about Hot device Identity


Guo, Min wrote:

> I can not find the file dev in the /sys/class/usb, does it means that 
> Udev does not support my USB CDROM? If not, which file is behalf of 
> my USB CDROM device?
> 

I think you've missed the point here. There is no such thing as a 
"generic" USB device that could have a dev file for it in 
/sys/class/usb. For a device to have a dev file, it must have some 
sort of device-specific driver talking to it. If that driver exists 
and is loaded, it will (or should) have a class of its own under 
/sys/class, and the dev file will be there.

In the case of a USB CD-ROM, that is handled by the usb-storage 
driver, but that driver _still_ does not create a dev file, because it 
does not directly expose itself to userspace (there is no way to talk 
to the usb-storage driver itself). usb-storage connects the device the 
  SCSI midlayer, which then attaches the sd (SCSI disk) driver to the 
device. _That_ driver is actually a real device that the user can 
interact with, so it creates a dev file in the appropriate place, 
namely /sys/block. You can think of /sys/block as a special-case 
class, and consider it equivalent to /sys/class/block (although it's 
more than that).

The only devices that will ever have "dev" files in /sys for them are 
those that can actually can communicated with from userspace. There is 
no need for userspace to treat your USB CD-ROM as a USB CD-ROM, 
instead it just considers it to be a generic disk (block) device that 
holds read-only media. I don't see any reason this device will ever 
generate any directories under /sys/class/... with dev files in them, 
they're not necessary.

But, this has nothing to do with whether udev can support your device 
or not and create a node in /dev for it. udev should be able to do 
exactly that, but I don't know whether it currently looks only at 
/sys/class (which I think is the case) or whether it also looks at 
/sys/block.



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