Get USB Device Class Type and Mount point

[Abhijit Pawar]

Hi Greg,
On 02/09/2012 05:53 PM, Greg KH wrote:
> On Thu, Feb 09, 2012 at 11:40:16AM +0530, Abhijit Pawar wrote:
>> Hi ,
>> Is there any way we can get the class type of the attached USB device through
>> struct usb_device in a kernel module?
>>
>> I tried getting the device descriptor and interface descriptor and then use
>> them to get the Device and Interface Class and Subclass.
>>
>> struct usb_device_descriptor *descriptor =&usbDev->descriptor;
>>   
>> struct usb_interface_descriptor *idesc = to_usb_interface(usbDev);
>>
>> Whenever I run my kernel module, I get 0 for DeviceClass and Interface Class. I
>> checked the meaning and it says its the information and to be gathered through
>> interface.
> That is correct, look at the interface pointer given to your driver.
>
>> Am I missing something here? What I want is to get the mount point / device
>> path of the USB devices. Like for Storage Device I would like to get its mount
>> path and for HID I would like to get its device path.
> Both of those things make no sense within the kernel, and you will not
> be able to detect them from your driver, especially as it is not your
> driver bound to this type of device, the in-kernel drivers are.  Also,
> these have nothing to do with the class type of a device's interface.
Yes. As I am dealing with USB Core, I am not in  a position to get the 
interface directly. However I checked the usb_dump_interface_descriptor( 
) from usb/core/devices.c and it gives the interface class ( 8 for 
Storage) correctly.
Isnt it forwared to my module which is relying on the linux usb notifier 
chain? This chain gives me the device pointer and I am trying to 
enumerate its interface to know its class.
>
> What are you trying to solve here that you feel you need this
> information that is easily found from userspace?
I am trying to use USB notifier chains to get the device details and 
then find out its mount path ( in case of Storage).  Are you saying that 
I should be looking into sysFS and udev rules for getting this mount path?


> greg k-h