linux以C方式和内核交互监听键盘[香橙派搞机日记]

最近在深入研究我的香橙派，不可避免的遇到了怎么认识和使用Linux内核的问题。 我给自己留了一个简单的任务：使用原生C来监听内核，实现读取键盘的消息。

CSDN上也有其他文章来解决这个问题，不过要么是技术不达标（直接和终端交互显然不是我们想要的，这只是一个取巧的方案），要么是收费文章🥲 。楼主也是查阅了很多资料才解决了这个问题。如果这个方案解决了你的问题，还请你点赞，评论，收藏。您的支持是我的动力

如果你要学习知识，那可以从头读下去，如果你要快速使用，可以从 evtest 这个部分开始读，源代码贴在后面

接口在哪里？

在linux中，一切都是文件。哪怕你是一个物理设备，在内核中，你也得有个文件接口！

两个关键文件夹

/dev/input/

所有的设备，都是在dev 目录下统一管理的。让我们看看
/dev/input/

orangepi@orangepi3b:/dev/input$ ls
by-id	 event1   event12  event15  event18  event4  event7
by-path  event10  event13  event16  event2   event5  event8
event0	 event11  event14  event17  event3   event6  event9
orangepi@orangepi3b:/dev/input$ ls -l
total 0
drwxr-xr-x 2 root root     220 Apr 11 11:34 by-id
drwxr-xr-x 2 root root     280 Apr 11 11:34 by-path
crw-rw---- 1 root input 13, 64 Apr  6 12:37 event0
crw-rw---- 1 root input 13, 65 Apr  6 12:37 event1
crw-rw---- 1 root input 13, 74 Apr 11 11:34 event10
crw-rw---- 1 root input 13, 75 Apr 11 11:34 event11
crw-rw---- 1 root input 13, 76 Apr 11 11:34 event12
crw-rw---- 1 root input 13, 77 Apr 11 11:34 event13
crw-rw---- 1 root input 13, 78 Apr 11 11:34 event14
crw-rw---- 1 root input 13, 79 Apr 11 11:34 event15
crw-rw---- 1 root input 13, 80 Apr 11 11:34 event16
crw-rw---- 1 root input 13, 81 Apr 11 11:34 event17
crw-rw---- 1 root input 13, 82 Apr 11 11:34 event18
crw-rw---- 1 root input 13, 66 Apr  6 12:37 event2
crw-rw---- 1 root input 13, 67 Apr 11 11:34 event3
crw-rw---- 1 root input 13, 68 Apr 11 11:34 event4
crw-rw---- 1 root input 13, 69 Apr 11 11:34 event5
crw-rw---- 1 root input 13, 70 Apr 11 11:34 event6
crw-rw---- 1 root input 13, 71 Apr 11 11:34 event7
crw-rw---- 1 root input 13, 72 Apr 11 11:34 event8
crw-rw---- 1 root input 13, 73 Apr 11 11:34 event9

每个event代表一个事件，那么，怎么知道事件和设备的对应呢？ 这要借助/proc/bus
（这个部分的知识点参考了蓝天居士的博客，他是一位水平非常高的专家，大家可以学习一下）

/proc/bus/input/devices

让我们转到这个目录

orangepi@orangepi3b:/proc$ cd bus
orangepi@orangepi3b:/proc/bus$ ls
input  pci
orangepi@orangepi3b:/proc/bus$ cd input
orangepi@orangepi3b:/proc/bus/input$ ls
devices  handlers
orangepi@orangepi3b:/proc/bus/input$ cd devices
bash: cd: devices: Not a directory
orangepi@orangepi3b:/proc/bus/input$ cd devices 
bash: cd: devices: Not a directory
orangepi@orangepi3b:/proc/bus/input$ tree
.
├── devices
└── handlers0 directories, 2 files

看看设备信息，信息比较长。我们要拆开来看

event0是什么

orangepi@orangepi3b:/proc/bus/input$ cat devices 
I: Bus=0019 Vendor=0001 Product=0001 Version=0100
N: Name="hdmi_cec_key"
P: Phys=hdmi_cec_key/input0
S: Sysfs=/devices/platform/fe0a0000.hdmi/dw-hdmi-cec.1.auto/input/input0
U: Uniq=
H: Handlers=event0 
B: PROP=0
B: EV=3
B: KEY=10000000000000 0

I: Bus=0019 Vendor=0001 Product=0001 Version=0100 这个信息：设备挂在总线19下，厂商ID(vendor=0001) 产品ID(Product=0001)
产品版本Version=0100

N: Name="hdmi_cec_key" 标识设备名称和用途

P: Phys=hdmi_cec_key/input0 设备的物理路径，标识设备在系统中的物理位置

S: Sysfs=/devices/platform/fe0a0000.hdmi/dw-hdmi-cec.1.auto/input/input0 设备早sysfs 文件系统中的路径，用于内核和用户空间交互

U: Uniq= 设备唯一标识符号，这里为空

H: Handlers=event0 设备对应的事件处理程序是event0 标识该设备的输入事件通过events0暴露 这个信息是关键信息

B: PROP=0 设备属性标识，这里为0 标识无特殊属性

B: EV=3 标识设备支持的事件类型

B: KEY=10000000000000 0 标识设备支持的按键键值

---

鼠标

可见，一个设备可以有多个输入

I: Bus=0003 Vendor=046d Product=c08b Version=0111
N: Name="Logitech G502 HERO Gaming Mouse"
P: Phys=usb-fd800000.usb-1.1/input0
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.1/1-1.1:1.0/0003:046D:C08B.0001/input/input3
U: Uniq=0470323E3232
H: Handlers=event3 
B: PROP=0
B: EV=17
B: KEY=ffff0000 0 0 0 0
B: REL=1943
B: MSC=10I: Bus=0003 Vendor=046d Product=c08b Version=0111
N: Name="Logitech G502 HERO Gaming Mouse Keyboard"
P: Phys=usb-fd800000.usb-1.1/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.1/1-1.1:1.1/0003:046D:C08B.0002/input/input4
U: Uniq=0470323E3232
H: Handlers=sysrq kbd event4 
B: PROP=0
B: EV=100013
B: KEY=1000000000007 ff800000000007ff febeffdfffefffff fffffffffffffffe
B: MSC=10I: Bus=0003 Vendor=046d Product=c08b Version=0111
N: Name="Logitech G502 HERO Gaming Mouse Consumer Control"
P: Phys=usb-fd800000.usb-1.1/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.1/1-1.1:1.1/0003:046D:C08B.0002/input/input5
U: Uniq=0470323E3232
H: Handlers=kbd event5 
B: PROP=0
B: EV=1f
B: KEY=306ff 0 0 483ffff17aff32d bfd4444600000000 1 130ff38b17c000 677bfad9415fed 9ed68000004400 10000002
B: REL=1040
B: ABS=100000000
B: MSC=10I: Bus=0003 Vendor=046d Product=c08b Version=0111
N: Name="Logitech G502 HERO Gaming Mouse System Control"
P: Phys=usb-fd800000.usb-1.1/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.1/1-1.1:1.1/0003:046D:C08B.0002/input/input6
U: Uniq=0470323E3232
H: Handlers=kbd event6 
B: PROP=0
B: EV=13
B: KEY=c000 10000000000000 0
B: MSC=10

键盘

I: Bus=0003 Vendor=320f Product=5055 Version=0110
N: Name="VXE V87 VXE V87"
P: Phys=usb-fd800000.usb-1.3/input0
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.3/1-1.3:1.0/0003:320F:5055.0003/input/input9
U: Uniq=2020-12-15
H: Handlers=sysrq kbd leds event7 
B: PROP=0
B: EV=120013
B: KEY=1000000000007 ff9f207ac14057ff febeffdfffefffff fffffffffffffffe
B: MSC=10
B: LED=1fI: Bus=0003 Vendor=320f Product=5055 Version=0110
N: Name="VXE V87 VXE V87 Keyboard"
P: Phys=usb-fd800000.usb-1.3/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.3/1-1.3:1.1/0003:320F:5055.0004/input/input10
U: Uniq=2020-12-15
H: Handlers=kbd event8 
B: PROP=0
B: EV=100013
B: KEY=ff80000000000000 80b0ffcd01cfffff febffbffdffffffe
B: MSC=10I: Bus=0003 Vendor=320f Product=5055 Version=0110
N: Name="VXE V87 VXE V87 System Control"
P: Phys=usb-fd800000.usb-1.3/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.3/1-1.3:1.1/0003:320F:5055.0004/input/input11
U: Uniq=2020-12-15
H: Handlers=kbd event9 
B: PROP=0
B: EV=13
B: KEY=c000 10000000000000 0
B: MSC=10I: Bus=0003 Vendor=320f Product=5055 Version=0110
N: Name="VXE V87 VXE V87 Consumer Control"
P: Phys=usb-fd800000.usb-1.3/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.3/1-1.3:1.1/0003:320F:5055.0004/input/input12
U: Uniq=2020-12-15
H: Handlers=kbd event10 
B: PROP=0
B: EV=1f
B: KEY=3f000307ff 0 0 483ffff17aff32d bfd4444600000000 1 130ff38b17d000 677bfad9415fed 19ed68000004400 10000002
B: REL=1040
B: ABS=100000000
B: MSC=10I: Bus=0003 Vendor=320f Product=5055 Version=0110
N: Name="VXE V87 VXE V87"
P: Phys=usb-fd800000.usb-1.3/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.3/1-1.3:1.1/0003:320F:5055.0004/input/input13
U: Uniq=2020-12-15
H: Handlers=event11 
B: PROP=0
B: EV=9
B: ABS=10000000000I: Bus=0003 Vendor=320f Product=5055 Version=0110
N: Name="VXE V87 VXE V87 Mouse"
P: Phys=usb-fd800000.usb-1.3/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.3/1-1.3:1.1/0003:320F:5055.0004/input/input14
U: Uniq=2020-12-15
H: Handlers=event12 
B: PROP=0
B: EV=17
B: KEY=1f0000 0 0 0 0
B: REL=1943
B: MSC=10I: Bus=0003 Vendor=320f Product=5088 Version=0111
N: Name="Telink VXE V87 2.4G Dongle"
P: Phys=usb-fd800000.usb-1.4/input0
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.4/1-1.4:1.0/0003:320F:5088.0007/input/input21
U: Uniq=
H: Handlers=sysrq kbd leds event13 
B: PROP=0
B: EV=120013
B: KEY=1000000000007 ff9f207ac14057ff febeffdfffefffff fffffffffffffffe
B: MSC=10
B: LED=1fI: Bus=0003 Vendor=320f Product=5088 Version=0111
N: Name="Telink VXE V87 2.4G Dongle Keyboard"
P: Phys=usb-fd800000.usb-1.4/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.4/1-1.4:1.1/0003:320F:5088.0008/input/input22
U: Uniq=
H: Handlers=kbd event14 
B: PROP=0
B: EV=100013
B: KEY=ff80000000000000 80b0ffcd01cfffff febffbffdffffffe
B: MSC=10I: Bus=0003 Vendor=320f Product=5088 Version=0111
N: Name="Telink VXE V87 2.4G Dongle System Control"
P: Phys=usb-fd800000.usb-1.4/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.4/1-1.4:1.1/0003:320F:5088.0008/input/input23
U: Uniq=
H: Handlers=kbd event15 
B: PROP=0
B: EV=13
B: KEY=c000 10000000000000 0
B: MSC=10I: Bus=0003 Vendor=320f Product=5088 Version=0111
N: Name="Telink VXE V87 2.4G Dongle Consumer Control"
P: Phys=usb-fd800000.usb-1.4/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.4/1-1.4:1.1/0003:320F:5088.0008/input/input24
U: Uniq=
H: Handlers=kbd event16 
B: PROP=0
B: EV=1f
B: KEY=3f000307ff 0 0 483ffff17aff32d bfd4444600000000 1 130ff38b17d000 677bfad9415fed 19ed68000004400 10000002
B: REL=1040
B: ABS=100000000
B: MSC=10I: Bus=0003 Vendor=320f Product=5088 Version=0111
N: Name="Telink VXE V87 2.4G Dongle"
P: Phys=usb-fd800000.usb-1.4/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.4/1-1.4:1.1/0003:320F:5088.0008/input/input25
U: Uniq=
H: Handlers=event17 
B: PROP=0
B: EV=9
B: ABS=10000000000I: Bus=0003 Vendor=320f Product=5088 Version=0111
N: Name="Telink VXE V87 2.4G Dongle Mouse"
P: Phys=usb-fd800000.usb-1.4/input1
S: Sysfs=/devices/platform/fd800000.usb/usb1/1-1/1-1.4/1-1.4:1.1/0003:320F:5088.0008/input/input26
U: Uniq=
H: Handlers=event18 
B: PROP=0
B: EV=17
B: KEY=1f0000 0 0 0 0
B: REL=1943
B: MSC=10

看起来有些复杂。不过我们很容易看出event* 和设备的对应关系。你觉得有些麻烦？ 已经有人为我们制作了工具！

使用evtest来测试你的输入设备

orangepi@orangepi3b:~/bop_code$ sudo apt install evtest
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
evtest is already the newest version (1:1.34-1).
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

扫描设备

orangepi@orangepi3b:~/bop_code$ sudo evtest
No device specified, trying to scan all of /dev/input/event*
Available devices:
/dev/input/event0:      hdmi_cec_key
/dev/input/event1:      rk805 pwrkey
/dev/input/event2:      rockchip-rk809 Headset
/dev/input/event3:      Logitech G502 HERO Gaming Mouse
/dev/input/event4:      Logitech G502 HERO Gaming Mouse Keyboard
/dev/input/event5:      Logitech G502 HERO Gaming Mouse Consumer Control
/dev/input/event6:      Logitech G502 HERO Gaming Mouse System Control
/dev/input/event7:      VXE V87 VXE V87
/dev/input/event8:      VXE V87 VXE V87 Keyboard
/dev/input/event9:      VXE V87 VXE V87 System Control
/dev/input/event10:     VXE V87 VXE V87 Consumer Control
/dev/input/event11:     VXE V87 VXE V87
/dev/input/event12:     VXE V87 VXE V87 Mouse
/dev/input/event13:     Telink VXE V87 2.4G Dongle
/dev/input/event14:     Telink VXE V87 2.4G Dongle Keyboard
/dev/input/event15:     Telink VXE V87 2.4G Dongle System Control
/dev/input/event16:     Telink VXE V87 2.4G Dongle Consumer Control
/dev/input/event17:     Telink VXE V87 2.4G Dongle
/dev/input/event18:     Telink VXE V87 2.4G Dongle Mouse

选取并监听

这里以键盘为例子

Select the device event number [0-18]: 7
Input driver version is 1.0.1
Input device ID: bus 0x3 vendor 0x320f product 0x5055 version 0x110
Input device name: "VXE V87 VXE V87"
Supported events:Event type 0 (EV_SYN)Event type 1 (EV_KEY)Event code 1 (KEY_ESC)Event code 2 (KEY_1)Event code 3 (KEY_2)Event code 4 (KEY_3)....Event code 190 (KEY_F20)Event code 191 (KEY_F21)Event code 192 (KEY_F22)Event code 193 (KEY_F23)Event code 194 (KEY_F24)Event code 240 (KEY_UNKNOWN)Event type 4 (EV_MSC)Event code 4 (MSC_SCAN)Event type 17 (EV_LED)Event code 0 (LED_NUML) state 0Event code 1 (LED_CAPSL) state 0Event code 2 (LED_SCROLLL) state 0Event code 3 (LED_COMPOSE) state 0Event code 4 (LED_KANA) state 0
Key repeat handling:Repeat type 20 (EV_REP)Repeat code 0 (REP_DELAY)Value    250Repeat code 1 (REP_PERIOD)Value     33
Properties:
Testing ... (interrupt to exit)
Event: time 1744374523.592185, type 4 (EV_MSC), code 4 (MSC_SCAN), value 70028
Event: time 1744374523.592185, type 1 (EV_KEY), code 28 (KEY_ENTER), value 0
Event: time 1744374523.592185, -------------- SYN_REPORT ------------
Event: time 1744374526.435125, type 4 (EV_MSC), code 4 (MSC_SCAN), value 70013
Event: time 1744374526.435125, type 1 (EV_KEY), code 25 (KEY_P), value 1
Event: time 1744374536.039071, -------------- SYN_REPORT ------------
Event: time 1744374536.207057, type 4 (EV_MSC), code 4 (MSC_SCAN), value 70006
Event: time 1744374536.207057, type 1 (EV_KEY), code 46 (KEY_C), value 1
Event: time 1744374536.207057, -------------- SYN_REPORT ------------
Event: time 1744374536.295063, type 4 (EV_MSC), code 4 (MSC_SCAN), value 70006
Event: time 1744374536.295063, type 1 (EV_KEY), code 46 (KEY_C), value 0
Event: time 1744374536.295063, -------------- SYN_REPORT ------------

使用代码实现内核监听

我们在刚刚，已经获得了键盘输入在event7的信息
！！！注意！ 你必须使用evtest来观察你的键盘的正确位置！！！ 否则代码会失败！
下面按照这个来写，这是源代码

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#include <linux/input.h>int main(int argc, char **argv) {const char* devloc = "/dev/input/event7";int fd = open(devloc, O_RDONLY) ;if (fd == -1) {perror("无法打开输入设备");return 1;}struct input_event ev;while(true){ssize_t n = read(fd , &ev ,sizeof(ev));if(n ==-1){perror("this error  \n");break;}if(n!= sizeof(ev)){continue;}if(ev.type ==EV_KEY && ev.value ==1){printf(" key!!!\n");switch ((ev.code)){case  KEY_P:printf("hello");break;case  KEY_K:printf(" keyboard");break;            default:break;}}}close(fd);return 0;
}

让我们把代码封装成类吧

#include <iostream>
#include <thread>
#include <unordered_map>
#include <functional>#include <linux/input.h>
#include <fcntl.h>  //open函数在这个库
#include <unistd.h> //read在这个库class bop_keylistener
{
private:int fd;std::unordered_map<int, std::function<void()>> keyCallbacks;std::thread listenerThread;struct input_event ev;bool running = true;int millsec_wait ;void listenkey(){while(running){ssize_t n = read(fd , &ev ,sizeof(ev));if(n ==-1){std::cerr << "this event message  error  "<<std::endl;}if(n!= sizeof(ev)){continue;}if(ev.type ==EV_KEY && ev.value ==1){for(const auto& pair :keyCallbacks){auto keyi=pair.first;if(keyi == ev.code){pair.second();}}std::this_thread::sleep_for(std::chrono::milliseconds(millsec_wait));}}}
public:bop_keylistener(const char* devloc , int millsecwait = 50){millsec_wait =millsecwait;fd = open(devloc, O_RDONLY) ;if (fd == -1) {perror("无法打开输入设备");}listenerThread = std::thread(&bop_keylistener::listenkey, this);}~bop_keylistener(){running = false;if (listenerThread.joinable()) {listenerThread.join();}}// 注册按键和对应的回调函数void registerKeyCallback(int key, const std::function<void()>& callback) {keyCallbacks[key] = callback;}};// 示例回调函数
void exampleCallback() {std::cout << "Example callback executed!" << std::endl;
}int main() {bop_keylistener mkeyl("/dev/input/event7" );// 注册按键 'A' 和对应的回调函数mkeyl.registerKeyCallback(KEY_1, exampleCallback);// 保持主线程运行std::this_thread::sleep_for(std::chrono::hours(1));return 0;
}

创作不易，还请多多支持