Get USB Device Class Type and Mount point

[Abhijit Pawar]

On 02/09/2012 08:17 PM, Greg KH wrote:
> On Thu, Feb 09, 2012 at 07:18:53PM +0530, Abhijit Pawar wrote:
>> 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.
> Ah, I thought you were a "real" driver.  Yes, just enumerate the
> interfaces of the device.
>
> Have a pointer to your code anywhere?
>
>>> 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?
> I'm saying you shouldn't be doing any of this from within the kernel at
> all, as again, it can be trivially found from userspace today with no
> kernel changes needed.
>
> Step back again, what is the problem you are trying to solve?
>
> greg k-h
I am trying to find out if any storage disk is connected to USB port and 
get its mount so that I an encrypt that mount with encrypted filesystem.

Regards,
Abhijit Pawar