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I'm doing a Linux kernel module which every time a keyboard is plugged in it prints a message like "Keyboard connected!"

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/usb.h>
#include <linux/usb/input.h>
#include <linux/hid.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("rcortes-");
MODULE_DESCRIPTION("Load when a Keyboard is Plugged In");
MODULE_VERSION("0.01");

static int __init kb_init(void)
{
    printk(KERN_INFO "Keyboard has been connected!\n");
    return 0;
}

static void __exit kb_exit(void)
{
    printk(KERN_INFO "Module clean up!\n");
}

module_init(kb_init);
module_exit(kb_exit);

I have a udev rule to load the module when it detects the keyboard:

ACTION=="add", SUBSYSTEM=="usb", ATTRS{bInterfaceClass}=="03", ATTRS{bInterfaceSubClass}=="01", ATTRS{bInterfaceProtocol}=="01", RUN+="/usr/sbin/insmod /home/LinuxKernelAssignments/ex04/basic/kb_hotplug.ko"

Now, the problem is that when I connect the keyboard, my udev rule fails with exit code 1. I guess the problem is that usbhid is already registering the keyboard before udev loads the module but I want kb_hotplug to be executed first.

What 'dmesg -w' prints:

[ 1285.506100] usb 2-2: new low-speed USB device number 8 using ohci-pci
[ 1286.345073] usb 2-2: New USB device found, idVendor=04d9, idProduct=1702, bcdDevice=4.06
[ 1286.345086] usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 1286.345091] usb 2-2: Product: USB Keyboard
[ 1286.345096] usb 2-2: Manufacturer: 
[ 1286.385105] input: USB Keyboard as /devices/pci0000:0000:0000:06.0/usb2/2-2/2-2:1.0/0003:04D9:1702.0012/input/input29
[ 1286.920473] hid-generic 0003:04D9:1702.0012: input,hidraw1: USB HID v1.10 Keyboard [USB Keyboard] on usb-0000:00:06.0-2/input0
[ 1286.963103] input: USB Keyboard System Control as /devices/pci0000:0000:0000:06.0/usb2/2-2/2-2:1.1/0003:04D9:1702.0013/input/input30
[ 1287.015041] input: USB Keyboard Consumer Control as /devices/pci0000:0000:0000:06.0/usb2/2-2/2-2:1.1/0003:04D9:1702.0013/input/input31
[ 1287.015194] hid-generic 0003:04D9:1702.0013: input,hidraw2: USB HID v1.10 Device [USB Keyboard] on usb-0000:00:06.0-2/input1
[ 1287.038807] (udev-worke[612]: 2-2:1.0: Process '/usr/sbin/insmod /home/LinuxKernelAssignments/ex04/basic/kb_hotplug.ko' failed with exit code 1.

I'm using a Linux from scratch distro.

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  • I've edited your post, mostly to fix the formatting. Please pay attention: to enable syntax coloring, you have to specify the language in the line of the opening Markdown code fence. For example: ~~~c++. For plain text output, specify ~~~text. Commented Aug 18 at 7:01
  • The issue is that your module is trying to load after the USB HID driver has already claimed the keyboard device. The exit code 1 from insmod likely means the module is already loaded or there's a dependency issue. Here are several solutions: Solution 1: Use USB device driver approach instead of udev Commented Nov 1 at 16:39
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