有没有办法检查 /dev/input/ 中的哪个事件文件用于键盘输入？

Question

Basically, what I am trying to do is capture keyboard input from the user, using files in "/dev/input/". However, a problem I have come across is that the file which handles keyboard input is different on event files. What do I mean by this? Well, on my specific machine, "/dev/input/event5" works with this program, but I've seen that, on some people's machines, the file might be event4, event0, event3, or even event17.

Is there a way that I can programmatically figure out which file handles keyboard input?

If you want to test the code, make sure you run with root privileges. You need them to open any files in "/dev/input/".

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <linux/input.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <signal.h>
 
#define UK "UNKNOWN"
#define ESCAPE(key) (key == KEY_ESC)
#define SHIFT(key)  ((key == KEY_LEFTSHIFT) || (key == KEY_RIGHTSHIFT))
 
static const char *keycodes[] =
{
    "RESERVED", "ESC", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0",
    "-", "=", "BACKSPACE", "TAB", "q", "w", "e", "r", "t", "y", "u", "i",
    "o", "p", "[", "]", "ENTER", "L_CTRL", "a", "s", "d", "f", "g", "h",
    "j", "k", "l", ";", "'", "`", "L_SHIFT", "\\", "z", "x", "c", "v", "b",
    "n", "m", ",", ".", "/", "R_SHIFT", "*", "L_ALT", "SPACE", "CAPS_LOCK", 
    "F1", "F2", "F3", "F4", "F5", "F6", "F7", "F8", "F9", "F10", "NUM_LOCK",
    "SCROLL_LOCK", "NL_7", "NL_8", "NL_9", "-", "NL_4", "NL5",
    "NL_6", "+", "NL_1", "NL_2", "NL_3", "INS", "DEL", UK, UK, UK,
    "F11", "F12", UK, UK,   UK, UK, UK, UK, UK, "R_ENTER", "R_CTRL", "/", 
    "PRT_SCR", "R_ALT", UK, "HOME", "UP", "PAGE_UP", "LEFT", "RIGHT", "END", 
    "DOWN", "PAGE_DOWN", "INSERT", "DELETE", UK, UK, UK, UK,UK, UK, UK, 
    "PAUSE"
};
 
static const char *shifted_keycodes[] =
{
    "RESERVED", "ESC", "!", "@", "#", "$", "%", "^", "&", "*", "(", ")", 
    "_", "+", "BACKSPACE", "TAB", "Q", "W", "E", "R", "T", "Y", "U", "I", 
    "O", "P", "{", "}", "ENTER", "L_CTRL", "A", "S", "D", "F", "G", "H", 
    "J", "K", "L", ":", "\"", "~", "L_SHIFT", "|", "Z", "X", "C", "V", "B", 
    "N", "M", "<", ">", "?", "R_SHIFT", "*", "L_ALT", "SPACE", "CAPS_LOCK", 
    "F1", "F2", "F3", "F4", "F5", "F6", "F7", "F8", "F9", "F10", "NUM_LOCK", 
    "SCROLL_LOCK", "HOME", "UP", "PGUP", "-", "LEFT", "NL_5", 
    "R_ARROW", "+", "END", "DOWN", "PGDN", "INS", "DEL", UK, UK, UK, 
    "F11", "F12", UK, UK,   UK, UK, UK, UK, UK, "R_ENTER", "R_CTRL", "/", 
    "PRT_SCR", "R_ALT", UK, "HOME", "UP", "PAGE_UP", "LEFT", "RIGHT", "END", 
    "DOWN", "PAGE_DOWN", "INSERT", "DELETE", UK, UK, UK, UK,UK, UK, UK, 
    "PAUSE"
};
 
static int running;
static int keyboard_fd;
 
static void sig_handler(int signo)
{
    running = 0;
}
 
void input_demo_init(char *keyboard_eventfile)
{
    signal(SIGINT, sig_handler);
 
    running = 1;
 
    if ((keyboard_fd = open(keyboard_eventfile, O_RDONLY)) < 0) {
        fprintf(stderr, "\nUnable to read from the device\n");
        exit(EXIT_FAILURE);
    }
}
 
void input_demo_exit(void)
{
    close(keyboard_fd);
}
 
void input_demo_run(void)
{
    int shift_flag = 0;
    struct input_event event;
 
    while (running) {
        read(keyboard_fd, &event, sizeof(event));
 
        /* If a key from the keyboard is pressed */
        if (event.type == EV_KEY && event.value == 1) {
            if (ESCAPE(event.code))
                return;
 
            if (SHIFT(event.code))
                shift_flag = event.code;
 
            if (shift_flag && !SHIFT(event.code))
                printf("%s\n", shifted_keycodes[event.code]);
            
            else if (!shift_flag && !SHIFT(event.code))
                printf("%s\n", keycodes[event.code]);
        }
        else {
            /* If a key from the keyboard is released */
            if (event.type == EV_KEY && event.value == 0)
                if (SHIFT(event.code))
                    shift_flag = 0;
        }
    }
}
 
int main(int argc, char **argv) {
 
    input_demo_init("/dev/input/event5");
    input_demo_run();
    input_demo_exit();
 
    return 0;
}

Answer 1

You can try

cat /proc/bus/input/devices

I: Bus=001e Vendor=0000 Product=0000 Version=0001
N: Name="vc4"
P: Phys=vc4/input0
S: Sysfs=/devices/platform/soc/fef00700.hdmi/rc/rc0/input1
U: Uniq=
H: Handlers=kbd event0
B: PROP=20
B: EV=100017
B: KEY=ffffc000000000 3ff 0 400000320fc200 40830c900000000 0 210300 49d2c040ec00 1e378000000000 8010000010000000
B: REL=3
B: MSC=10

I: Bus=001e Vendor=0000 Product=0000 Version=0001
N: Name="vc4"
P: Phys=vc4/input0
S: Sysfs=/devices/platform/soc/fef05700.hdmi/rc/rc1/input2
U: Uniq=
H: Handlers=kbd event1
B: PROP=20
B: EV=100017
B: KEY=ffffc000000000 3ff 0 400000320fc200 40830c900000000 0 210300 49d2c040ec00 1e378000000000 8010000010000000
B: REL=3
B: MSC=10

hope that can help you.