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I have been learning Kernel programming and taking the Eudyptula challenge, and task 5 requires me to modify a hello world module from an earlier task to be automatically loaded when a USB keyboard is plugged, and unloaded when the keyboard is unplugged.

Now, for the sake of it, I will not be posting my code here, because that would be a huge spoiler for this task and would ruin the fun of it for others. Basically, what it does is:

  1. Creates a struct usb_device_id array with one entry that binds my module to any usb keyboard
  2. Creates a struct usb_driver and initializes the proper fields; in particular, it references the usb device id table array that I created previously
  3. Uses the macro MODULE_DEVICE_TABLE to register the driver.

The register / unregister routines are working. I get the expected debugging messages when I manually load and unload the module.

I copied the module to /lib/modules/$(uname -r) and ran depmod -a. The module is added to modules.alias and modules.dep, but nothing happens when I plug / unplug the keyboard.

Further research showed that I should have a modules.usbmap file generated by depmod where the kernel keeps a mapping between devices and drivers to load. I don't have this file anywhere in my folders tree. I also don't have a modules.pcimap. I have checked the kernel configuration to make sure that loadable module support is enabled, as well as hotplugging support - they are.

This is Kubuntu 14.04 with self-compiled 3.16.0-rc5 kernel. What am I missing? I have gone through the kernel configuration and checked the most obvious options. I'm kind of stuck here. Any ideas?

Braiam
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Filipe Gonçalves
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2 Answers2

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You might be missing two things:

1.) An USB keyboard is typically not just a generic USB device, but a HID class device. Linux treats USB HID devices as a separate subclass. Have you taken this into account?

2.) modules.usbmap and modules.pcimap exist with some older versions of module/pci/usb utilities only. With modern versions, the information equivalent to what used to be in those files is included in modules.alias instead. Your research materials may have been obsolete.

Matti Kurkela
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  • I eventually made it, though I never got the module to load every time I plugged / unplugged the keyboard. Apparently, I was having a similar problem to http://www.linuxquestions.org/questions/programming-9/driver-development-usbhid-is-blocking-custom-device-driver-850287 - if I unload `usbhid`, then my module works as expected. – Filipe Gonçalves Sep 03 '14 at 16:59
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Here are my suggestions..

  1. Try registering by using vendor_id, product_id and check whether you are registering the for the correct hardware device.

You can try writing a rule in

/etc/udev/rules.d/10-local.rules

make sure it is identifying your hardware correctly. Following commands may help you:

udevadm monitor or udevadm monitor --env
udevadm info -a -p [/devices/pci0000:00/0000:00:1a.0/usb1/1-1 -> this has to be get from above command]
  1. Make sure you rmmod your module, clean all logs [sudo dmesg -c] and plug in the hardware.
Chand Priyankara
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