Need to intercept HID Keyboard events (and then block them)

Question

I've got a RFID USB device that registers as a HID device (A USB Keyboard more or less).

I'm looking for a way to capture this input, and block/filter it before it hits the normal keyboard event handler (and outputs the 10 digit RFID code to the console).

I would of course have to exclusively capture just this device, and leave the real keyboard input alone (or pass it along).

My initial idea was to block the device in UDEV (So the usbhid/event/kbd kernel module didn't bind to it) and write my own basic driver for this device - but I don't know where to begin, or if that'll even work.

What would be great (and I'm not sure if such a thing can be done) - is if I write a event-filter module that can sit in-line with the event driver and capture (then filter) the appropriate input from the RFID unit, but let everything else pass through. I imagine such a module wouldn't require much code, and would be the most practical.

Help?

[EDIT: I should add that Xorg is NOT installed - console only]

cat /proc/bus/input:
  I: Bus=0003 Vendor=0419 Product=0912 Version=0100
  N: Name="NewRoad Sem. NewRoad System PS2 Interface"
  P: Phys=usb-0000:00:1d.3-2/input0
  S: Sysfs=/devices/pci0000:00/0000:00:1d.3/usb5/5-2/5-2:1.0/input/input20
  U: Uniq=
  H: Handlers=sysrq kbd mouse0 event3
  B: PROP=0
  B: EV=120017
  B: KEY=70000 0 0 e080ffdf01cfffff fffffffffffffffe
  B: REL=103
  B: MSC=10
  B: LED=1f

More info:

lsusb -d 0419:0912 -v
Bus 005 Device 019: ID 0419:0912 Samsung Info. Systems America, Inc.
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0         8
  idVendor           0x0419 Samsung Info. Systems America, Inc.
  idProduct          0x0912
  bcdDevice            0.01
  iManufacturer           1 NewRoad Sem.
  iProduct                2 NewRoad System PS2 Interface
  iSerial                 0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           34
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          4
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      1 Boot Interface Subclass
      bInterfaceProtocol      1 Keyboard
      iInterface              5
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.00
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength     119
         Report Descriptors:
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval              10
Device Status:     0x0000
  (Bus Powered)

Answer 1

So I whipped up a proof-of-concept app according to that post I found here

It does exactly what I require - just though I'd share my solution anyway.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <dirent.h>
#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <termios.h>
#include <signal.h>

int main(int argc, char* argv[])
{
    struct input_event ev[64];
    int fevdev = -1;
    int result = 0;
    int size = sizeof(struct input_event);
    int rd;
    int value;
    char name[256] = "Unknown";
    char *device = "/dev/input/event3";


    fevdev = open(device, O_RDONLY);
    if (fevdev == -1) {
        printf("Failed to open event device.\n");
        exit(1);
    }

    result = ioctl(fevdev, EVIOCGNAME(sizeof(name)), name);
    printf ("Reading From : %s (%s)\n", device, name);

    printf("Getting exclusive access: ");
    result = ioctl(fevdev, EVIOCGRAB, 1);
    printf("%s\n", (result == 0) ? "SUCCESS" : "FAILURE");

    while (1)
    {
        if ((rd = read(fevdev, ev, size * 64)) < size) {
            break;
        }

        value = ev[0].value;

        if (value != ' ' && ev[1].value == 1 && ev[1].type == 1) {
            printf ("Code[%d]\n", (ev[1].code));
        }
    }

    printf("Exiting.\n");
    result = ioctl(fevdev, EVIOCGRAB, 1);
    close(fevdev);
    return 0;
}

Answer 2

You can use EVIOCGRAB ioctl on an event device to capture it exclusively.