[HACK] Give hiddev a device link in sysfs

[HACK] Give hiddev a device link in sysfs

[Adam Kropelin]

I have a bunch of USB interface UPSes which are managed via the hiddev
interface. Recently I've been working on setting up a dedicated server
to manage them all. I'd like to use udev to manage the device nodes so
that I can have consistent naming no matter what USB port a particular
UPS happens to be plugged into. They have unique serial numbers, so a
udev.rules LABEL entry seemed the appropriate thing to do.

It didn't work. Eventually I tracked it to a bad device link in sysfs
(/sys/class/usb/hiddevN/device). Further investigation showed that the
broken link is due to hiddev's being not-quite-a-usb-device and having a
zero kobj with no parent, etc.

I cooked up the hack-job patch below and it seems to be working. Clearly
this isn't the right solution, but it's a starting point and it solves
my immediate need.

Bearing in mind that I'm a kobj newbie, can anyone suggest what the
right approach is to solve this problem? Do we actually want to grow a
legitimate kobj for the hiddev and register it? Comments in the code
imply that hiddev could eventually be severed from usb altogether. Is
there a shorter term solution that is workable?

Thanks for you input...
--Adam


--- linux-2.6.0-test11/drivers/usb/input/hiddev.c	Fri Oct 17 23:23:08 2003
+++ linux-2.6.0-test11-bk8/drivers/usb/input/hiddev.c	Mon Dec 15 19:05:19 2003
@@ -234,6 +234,7 @@
 static void hiddev_cleanup(struct hiddev *hiddev)
 {
 	usb_deregister_dev(&hiddev->intf, &hiddev_class);
+	kobject_put(hiddev->intf.dev.kobj.parent);
 	hiddev_table[hiddev->minor] = NULL;
 	kfree(hiddev);
 }
@@ -724,6 +725,14 @@
 		return -1;
 	memset(hiddev, 0, sizeof(struct hiddev));
 
+	strcpy(hiddev->intf.dev.kobj.name, hid->dev->dev.kobj.name);
+	kobject_get(hid->dev->dev.kobj.parent);
+	hiddev->intf.dev.kobj.parent = hid->dev->dev.kobj.parent;
+	hiddev->intf.dev.kobj.kset = NULL;
+	hiddev->intf.dev.kobj.ktype = NULL;
+	hiddev->intf.dev.kobj.dentry = NULL;
+	kobject_init(&hiddev->intf.dev.kobj);
+
  	retval = usb_register_dev(&hiddev->intf, &hiddev_class);
 	if (retval) {
 		err("Not able to get a minor for this device.");



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Re: [HACK] Give hiddev a device link in sysfs

[Greg KH]

On Mon, Dec 15, 2003 at 07:32:35PM -0500, Adam Kropelin wrote:
> I have a bunch of USB interface UPSes which are managed via the hiddev
> interface. Recently I've been working on setting up a dedicated server
> to manage them all. I'd like to use udev to manage the device nodes so
> that I can have consistent naming no matter what USB port a particular
> UPS happens to be plugged into. They have unique serial numbers, so a
> udev.rules LABEL entry seemed the appropriate thing to do.
> 
> It didn't work. Eventually I tracked it to a bad device link in sysfs
> (/sys/class/usb/hiddevN/device). Further investigation showed that the
> broken link is due to hiddev's being not-quite-a-usb-device and having a
> zero kobj with no parent, etc.
> 
> I cooked up the hack-job patch below and it seems to be working. Clearly
> this isn't the right solution, but it's a starting point and it solves
> my immediate need.

Yeah, hiddev is wierd.  It needs to dynamically allocate that interface
structure, and then a patch like this will start to make sense.  Right
now bad things can happen if you unload the hiddev module when you have
a file in sysfs open for that device.

But this patch is a start.  Care to finish it up?

thanks,

greg k-h


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Re: [HACK] Give hiddev a device link in sysfs

[Adam Kropelin]

Greg KH wrote:
> On Mon, Dec 15, 2003 at 07:32:35PM -0500, Adam Kropelin wrote:
>> (/sys/class/usb/hiddevN/device). Further investigation showed that
>> the broken link is due to hiddev's being not-quite-a-usb-device and
>> having a zero kobj with no parent, etc.
>> 
>> I cooked up the hack-job patch below and it seems to be working.
>> Clearly this isn't the right solution, but it's a starting point and
>> it solves my immediate need.
> 
> Yeah, hiddev is wierd.  It needs to dynamically allocate that
> interface structure, and then a patch like this will start to make
> sense.  Right now bad things can happen if you unload the hiddev
> module when you have a file in sysfs open for that device.
> 
> But this patch is a start.  Care to finish it up?

Sure...I'll have a chance to look at it after the holidays.

--Adam



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