Re: sysfs attribute example

[Greg KH <greg@kroah.com>]

On Mon, Jun 13, 2005 at 06:01:26PM -0500, Stephen Morgan wrote:
> > -----Original Message-----
> > From: Kay Sievers [mailto:kay.sievers@vrfy.org]
> > Sent: Friday, June 10, 2005 11:10 AM
> > To: Stephen Morgan
> > Cc: linux-hotplug-devel
> > Subject: Re: sysfs attribute example
> >
> >
> > On Fri, Jun 10, 2005 at 12:05:07PM -0500, Stephen Morgan wrote:
> > > Hello all,
> > >
> > > Can someone point me to an example of exporting a sysfs attribute from a
> > > driver?  (Or tell me if I shouldn't.)  I'm trying to get a
> > value from my USB
> > > device driver's probe() into an attribute so my udev .rules
> > file can pick it
> > > up.
> > >
> > > I've tried to follow what's in LDD 3rd ed. (page 374)
> > "...simply fill in an
> > > attribute and pass it to sysfs_create_file()"
> > >
> > > From my probe() function:
> > >
> > >   mydev->my_attribute.name = "my_attribute_name";
> > >   mydev->my_attribute.owner = THIS_MODULE;
> > >   mydev->my_attribute.mode = S_IRUGO;
> > >
> > >   sysfs_create_file(&(interface->class_dev->kobj),
> > &(mydev->my_attribute));
> > >
> > > When a device is probed, the file "my_attribute_name" shows up
> > in sysfs, but
> > > I get a "kernel NULL pointer dereference at virtual address 00000004"
> > > (address changes with the USB port I plug into).
> > >
> > > I'm also not seeing how to attach a value to the attribute.
> > So, clearly,
> > > I'm missing something crucial here :-)
> >
> > Sure, you do. :)
> >
> > Look for: DEVICE_ATTR() in the kernel code.
> >
> > Good luck,
> > Kay
> >
> 
> Hi Kay,
> 
> Thanks for your help.
> 
> This has gotten me much closer.  However, the show() function seems to be
> receiving a pointer to the usb_interface's class_device instead of its
> device.  Any ideas why?

Because that's where you registered the attribute?  :)

Care to show us your patch?

thanks,

greg k-h


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