Re: Need persistent node to USB port naming

[ocomber <ocomber@cmedltd.com>]

On Thu, 2005-05-12 at 14:58 -0500, Stephen Morgan wrote:
> Hello all,
> 
> I'm converting a driver for a USB device from Linux 2.4 to 2.6.  The device
> is embedded and the host is an embedded PC.  There may be as many as 6
> identical devices attached.  The only way they are differentiated is by the
> USB port they're plugged into - the cabling is fixed.  So, when the user
> asks for 'foo_dev0' for instance, he wants the first USB device - 'foo_dev1'
> should give him the 2nd device, etc.
> 
> Under 2.4, I created six nodes, assigning them minors 192 thru 197.  In the
> driver's probe(), I used usb_make_path to create an index to the device.
> For file ops, I used (MINOR(inode_p->i_rdev) - 192) to get an index from the
> node.
> 
> So far, under 2.6, the best approach I can see is to create a udev .rules
> file to make the nodes, like so: BUS="usb", PLACE="1-1", NAME="usb/foo_dev0"
> 
> Is this the best way to go, or have I overlooked something simpler?
> 
> Thanks
> 
> Stephen Morgan

If your driver is aware of which usb port it is plugged into, it could
turn this into a sysfs attribute which can be picked up by udev:

BUS="usb", KERNEL="foo", NAME="%k", SYMLINK="%s{USBPORT}"

It may be that the USB port already exists as a sysfs attribute without
you having to explicitly code this - I can't check this at the mo.

You can find what sysfs attributes exist for your devices with something
like:
udevinfo -a -p /class/usb/(DEVICE)

Hope this helps :0)

-Oli





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