Re: sysfs attribute example

[Kay Sievers <kay.sievers@vrfy.org>]

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


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