Linux Kernel（20.1）- Input device user program

這裡簡單的描述一下如何寫一個user program去讀去input device data，基本上，就是直接open /dev/inputN，然後將data mapping成struct input_event。

struct input_event {
    struct timeval time;
    __u16 type;
    __u16 code;
    __s32 value;
};

type: event type
code: key code for EV_KEY
摘入一段/usr/include/linux/input-event-codes.h

/*
 * Event types
 */
#define EV_SYN          0x00
#define EV_KEY          0x01
#define EV_REL          0x02
#define EV_ABS          0x03
#define EV_MSC          0x04
#define EV_SW           0x05
#define EV_LED          0x11
#define EV_SND          0x12
#define EV_REP          0x14
#define EV_FF           0x15
#define EV_PWR          0x16
#define EV_FF_STATUS        0x17
#define EV_MAX          0x1f
#define EV_CNT          (EV_MAX+1)

/*
 * Key code
 */
#define KEY_RESERVED        0
#define KEY_ESC         1
#define KEY_1           2
#define KEY_2           3
...

#define BTN_MISC        0x100
#define BTN_0           0x100
#define BTN_1           0x101
#define BTN_2           0x102
...

#define KEY_OK          0x160
#define KEY_SELECT      0x161
...

#include <stdio.h>
#include <errno.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <unistd.h>

#include <string.h>

#include <linux/input.h>

int main(int argc, char *argv[])
{
  struct input_event evt;
  int fd;
  fd = open(argv[1], O_RDONLY);
  if (fd < 0) {
    printf("open %s failed: %s/%d\n", argv[0], strerror(errno), errno);
    return -1;
  }

  while (1) {
    if (sizeof(evt) == read(fd, &evt, sizeof(evt))) {
      printf("type:%d, code:%d, val:%d\n", evt.type, evt.code, evt.value);
    } else {
      printf("read failed: %s/%d\n", strerror(errno), errno);
    }
  }
  return 0;
}

參考資料:
• Documentation/input/event-codes.rst