getevent命令解析

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我是靠谱客的博主敏感戒指，最近开发中收集的这篇文章主要介绍getevent命令解析，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

1.getevent命令使用
一般都是通过help来查询命令的使用方法，getevent命令也不例外

130|generic_x86:/ $ getevent -h
Usage: getevent [-t] [-n] [-s switchmask] [-S] [-v [mask]] [-d] [-p] [-i] [-l] [-q] [-c count] [-r] [device]
    -t: show time stamps
    -n: don't print newlines
    -s: print switch states for given bits
    -S: print all switch states
    -v: verbosity mask (errs=1, dev=2, name=4, info=8, vers=16, pos. events=32, props=64)
    -d: show HID descriptor, if available
    -p: show possible events (errs, dev, name, pos. events)
    -i: show all device info and possible events
    -l: label event types and names in plain text
    -q: quiet (clear verbosity mask)
    -c: print given number of events then exit
    -r: print rate events are received

其中最常用的参数就是：
-t: show time stamps—显示时间打印的时间
-l: label event types and names in plain text—这里表示把event事件类型名字打印出来
-r: print rate events are received—显示一下时间接受的速率

具体使用示例

127|generic_x86:/ $ gete -lrt
[  171811.520824] /dev/input/event1: EV_ABS       ABS_MT_TRACKING_ID   00000000
[  171811.520824] /dev/input/event1: EV_ABS       ABS_MT_POSITION_X    00002fff
[  171811.520824] /dev/input/event1: EV_ABS       ABS_MT_POSITION_Y    00006a76
[  171811.520824] /dev/input/event1: EV_ABS       ABS_MT_PRESSURE      00000400
[  171811.520824] /dev/input/event1: EV_SYN       SYN_REPORT           00000000
[  171811.560128] /dev/input/event1: EV_ABS       ABS_MT_POSITION_Y    00006a43
[  171811.560128] /dev/input/event1: EV_SYN       SYN_REPORT           00000000             rate 25
[  171811.563992] /dev/input/event1: EV_ABS       ABS_MT_POSITION_X    0000305a
[  171811.563992] /dev/input/event1: EV_ABS       ABS_MT_POSITION_Y    00006a10
[  171811.563992] /dev/input/event1: EV_SYN       SYN_REPORT           00000000             rate 258
[  171811.567507] /dev/input/event1: EV_ABS       ABS_MT_POSITION_Y    000069dd
[  171811.567507] /dev/input/event1: EV_SYN       SYN_REPORT           00000000             rate 284

示例解释打印对应的格式

[  171811.520824] /dev/input/event1: EV_ABS       ABS_MT_TRACKING_ID   00000000

[事件打印时间] 具体节点文件名:事件类型事件code 事件value

命令位置：
一般的命令都是在/system/bin下面，那么我们来/system/bin下找一个getevent

1|generic_x86:/system/bin $ ls -l | grep getevent
lrwxr-xr-x 1 root shell      7 2009-01-01 00:00 getevent -> toolbox

可以看到getevent命令是软连接的到toolbox的。

2.getevent源码分析
源码路径

system/core/toolbox/getevent.c
system/core/toolbox/toolbox.c
system/core/toolbox/tool.h

getevent命令链接到toolbox，那么入口函数就是toolbox的main函数了，就从toolbox的main函数开始讲起
以下是toolbox的源码分析,入口是main函数：

#define TOOL(name) int name##_main(int, char**);//这里会拼接名字
#include "tools.h"//这里内容其实就是TOOL(getevent) TOOL(getprop) TOOL(toolbox)
#undef TOOL

int main(int argc, char** argv) {
    char* cmd = strrchr(argv[0], '/');
    char* name = cmd ? (cmd + 1) : argv[0];//获取name就是getevent

    for (size_t i = 0; tools[i].name; i++) {
        if (!strcmp(tools[i].name, name)) {
            return tools[i].func(argc, argv);//这里会调用到getevent_main
        }
    }

    printf("%s: no such tooln", argv[0]);
    return 127;
}

这部分是getevent的源码，入口函数getevent_main函数

static struct pollfd *ufds;
static char **device_names;
static int nfds;

static void print_event(int type, int code, int value, int print_flags)
{
    const char *type_label, *code_label, *value_label;

    if (print_flags & PRINT_LABELS) {
        type_label = get_label(ev_labels, type);
        code_label = NULL;
        value_label = NULL;

        switch(type) {
            case EV_SYN:
                code_label = get_label(syn_labels, code);
                break;
            case EV_KEY:
                code_label = get_label(key_labels, code);
                value_label = get_label(key_value_labels, value);
                break;
            case EV_REL:
                code_label = get_label(rel_labels, code);
                break;
            case EV_ABS:
                code_label = get_label(abs_labels, code);
                switch(code) {
                    case ABS_MT_TOOL_TYPE:
                        value_label = get_label(mt_tool_labels, value);
                }
                break;
            case EV_MSC:
                code_label = get_label(msc_labels, code);
                break;
            case EV_LED:
                code_label = get_label(led_labels, code);
                break;
            case EV_SND:
                code_label = get_label(snd_labels, code);
                break;
            case EV_SW:
                code_label = get_label(sw_labels, code);
                break;
            case EV_REP:
                code_label = get_label(rep_labels, code);
                break;
            case EV_FF:
                code_label = get_label(ff_labels, code);
                break;
            case EV_FF_STATUS:
                code_label = get_label(ff_status_labels, code);
                break;
        }

        if (type_label)
            printf("%-12.12s", type_label);
        else
            printf("%04x        ", type);
        if (code_label)
            printf(" %-20.20s", code_label);
        else
            printf(" %04x                ", code);
        if (value_label)
            printf(" %-20.20s", value_label);
        else
            printf(" %08x            ", value);
    } else {
        printf("%04x %04x %08x", type, code, value);
    }
}

static void print_hid_descriptor(int bus, int vendor, int product)
{
    const char *dirname = "/sys/kernel/debug/hid";
    char prefix[16];
    DIR *dir;
    struct dirent *de;
    char filename[PATH_MAX];
    FILE *file;
    char line[2048];

    snprintf(prefix, sizeof(prefix), "%04X:%04X:%04X.", bus, vendor, product);

    dir = opendir(dirname);
    if(dir == NULL)
        return;
    while((de = readdir(dir))) {
        if (strstr(de->d_name, prefix) == de->d_name) {
            snprintf(filename, sizeof(filename), "%s/%s/rdesc", dirname, de->d_name);

            file = fopen(filename, "r");
            if (file) {
                printf("  HID descriptor: %snn", de->d_name);
                while (fgets(line, sizeof(line), file)) {
                    fputs("    ", stdout);
                    fputs(line, stdout);
                }
                fclose(file);
                puts("");
            }
        }
    }
    closedir(dir);
}


static int open_device(const char *device, int print_flags)
{
    int version;
    int fd;
    int clkid = CLOCK_MONOTONIC;
    struct pollfd *new_ufds;
    char **new_device_names;
    char name[80];
    char location[80];
    char idstr[80];
    struct input_id id;

    //打开devive对应的设备文件
    fd = open(device, O_RDONLY | O_CLOEXEC);
    if(fd < 0) {
        if(print_flags & PRINT_DEVICE_ERRORS)
            fprintf(stderr, "could not open %s, %sn", device, strerror(errno));
        return -1;
    }
    
    //做一些ioctl的操作
    if(ioctl(fd, EVIOCGVERSION, &version)) {
        if(print_flags & PRINT_DEVICE_ERRORS)
            fprintf(stderr, "could not get driver version for %s, %sn", device, strerror(errno));
        return -1;
    }
    if(ioctl(fd, EVIOCGID, &id)) {
        if(print_flags & PRINT_DEVICE_ERRORS)
            fprintf(stderr, "could not get driver id for %s, %sn", device, strerror(errno));
        return -1;
    }
    name[sizeof(name) - 1] = '';
    location[sizeof(location) - 1] = '';
    idstr[sizeof(idstr) - 1] = '';
    if(ioctl(fd, EVIOCGNAME(sizeof(name) - 1), &name) < 1) {
        //fprintf(stderr, "could not get device name for %s, %sn", device, strerror(errno));
        name[0] = '';
    }
    if(ioctl(fd, EVIOCGPHYS(sizeof(location) - 1), &location) < 1) {
        //fprintf(stderr, "could not get location for %s, %sn", device, strerror(errno));
        location[0] = '';
    }
    if(ioctl(fd, EVIOCGUNIQ(sizeof(idstr) - 1), &idstr) < 1) {
        //fprintf(stderr, "could not get idstring for %s, %sn", device, strerror(errno));
        idstr[0] = '';
    }

    if (ioctl(fd, EVIOCSCLOCKID, &clkid) != 0) {
        fprintf(stderr, "Can't enable monotonic clock reporting: %sn", strerror(errno));
        // a non-fatal error
    }

    new_ufds = realloc(ufds, sizeof(ufds[0]) * (nfds + 1));
    if(new_ufds == NULL) {
        fprintf(stderr, "out of memoryn");
        return -1;
    }
    ufds = new_ufds;
    new_device_names = realloc(device_names, sizeof(device_names[0]) * (nfds + 1));
    if(new_device_names == NULL) {
        fprintf(stderr, "out of memoryn");
        return -1;
    }
    device_names = new_device_names;

    if(print_flags & PRINT_DEVICE)
        printf("add device %d: %sn", nfds, device);
    if(print_flags & PRINT_DEVICE_INFO)
        printf("  bus:      %04xn"
               "  vendor    %04xn"
               "  product   %04xn"
               "  version   %04xn",
               id.bustype, id.vendor, id.product, id.version);
    if(print_flags & PRINT_DEVICE_NAME)
        printf("  name:     "%s"n", name);
    if(print_flags & PRINT_DEVICE_INFO)
        printf("  location: "%s"n"
               "  id:       "%s"n", location, idstr);
    if(print_flags & PRINT_VERSION)
        printf("  version:  %d.%d.%dn",
               version >> 16, (version >> 8) & 0xff, version & 0xff);

    if(print_flags & PRINT_POSSIBLE_EVENTS) {
        print_possible_events(fd, print_flags);
    }

    if(print_flags & PRINT_INPUT_PROPS) {
        print_input_props(fd);
    }
    if(print_flags & PRINT_HID_DESCRIPTOR) {
        print_hid_descriptor(id.bustype, id.vendor, id.product);
    }

    //将open的fd赋值给pollfd
    ufds[nfds].fd = fd;
    //有事件的时候才触发
    ufds[nfds].events = POLLIN;
    device_names[nfds] = strdup(device);
    nfds++;

    return 0;
}

int close_device(const char *device, int print_flags)
{
    int i;
    for(i = 1; i < nfds; i++) {
        if(strcmp(device_names[i], device) == 0) {
            int count = nfds - i - 1;
            if(print_flags & PRINT_DEVICE)
                printf("remove device %d: %sn", i, device);
            free(device_names[i]);
            memmove(device_names + i, device_names + i + 1, sizeof(device_names[0]) * count);
            memmove(ufds + i, ufds + i + 1, sizeof(ufds[0]) * count);
            nfds--;
            return 0;
        }
    }
    if(print_flags & PRINT_DEVICE_ERRORS)
        fprintf(stderr, "remote device: %s not foundn", device);
    return -1;
}

//读取/dev/input路径下面的节点内容变化
static int read_notify(const char *dirname, int nfd, int print_flags)
{
    int res;
    char devname[PATH_MAX];
    char *filename;
    char event_buf[512];
    int event_size;
    int event_pos = 0;
    struct inotify_event *event;

    res = read(nfd, event_buf, sizeof(event_buf));
    if(res < (int)sizeof(*event)) {
        if(errno == EINTR)
            return 0;
        fprintf(stderr, "could not get event, %sn", strerror(errno));
        return 1;
    }
    //printf("got %d bytes of event informationn", res);

    strcpy(devname, dirname);
    filename = devname + strlen(devname);
    *filename++ = '/';

    while(res >= (int)sizeof(*event)) {
        event = (struct inotify_event *)(event_buf + event_pos);
        //printf("%d: %08x "%s"n", event->wd, event->mask, event->len ? event->name : "");
        if(event->len) {
            strcpy(filename, event->name);
            if(event->mask & IN_CREATE) {
                open_device(devname, print_flags);
            }
            else {
                close_device(devname, print_flags);
            }
        }
        event_size = sizeof(*event) + event->len;
        res -= event_size;
        event_pos += event_size;
    }
    return 0;
}

//读取扫描路径下的节点
static int scan_dir(const char *dirname, int print_flags)
{
    char devname[PATH_MAX];
    char *filename;
    DIR *dir;
    struct dirent *de;
    dir = opendir(dirname);
    if(dir == NULL)
        return -1;
    strcpy(devname, dirname);
    filename = devname + strlen(devname);
    *filename++ = '/';
    while((de = readdir(dir))) {
        if(de->d_name[0] == '.' &&
           (de->d_name[1] == '' ||
            (de->d_name[1] == '.' && de->d_name[2] == '')))
            continue;
        strcpy(filename, de->d_name);
        //devname获取到事件名称，如:/dev/input/event3
        open_device(devname, print_flags);
    }
    closedir(dir);
    return 0;
}

//help的打印信息
static void usage(char *name)
{
    fprintf(stderr, "Usage: %s [-t] [-n] [-s switchmask] [-S] [-v [mask]] [-d] [-p] [-i] [-l] [-q] [-c count] [-r] [device]n", name);
    fprintf(stderr, "    -t: show time stampsn");
    fprintf(stderr, "    -n: don't print newlinesn");
    fprintf(stderr, "    -s: print switch states for given bitsn");
    fprintf(stderr, "    -S: print all switch statesn");
    fprintf(stderr, "    -v: verbosity mask (errs=1, dev=2, name=4, info=8, vers=16, pos. events=32, props=64)n");
    fprintf(stderr, "    -d: show HID descriptor, if availablen");
    fprintf(stderr, "    -p: show possible events (errs, dev, name, pos. events)n");
    fprintf(stderr, "    -i: show all device info and possible eventsn");
    fprintf(stderr, "    -l: label event types and names in plain textn");
    fprintf(stderr, "    -q: quiet (clear verbosity mask)n");
    fprintf(stderr, "    -c: print given number of events then exitn");
    fprintf(stderr, "    -r: print rate events are receivedn");
}

//toolbox的转换过来的getevent命令的入口函数
int getevent_main(int argc, char *argv[])
{
    int c;
    int i;
    int res;
    int get_time = 0;
    int print_device = 0;
    char *newline = "n";
    uint16_t get_switch = 0;
    struct input_event event;
    int print_flags = 0;
    int print_flags_set = 0;
    int dont_block = -1;
    int event_count = 0;
    int sync_rate = 0;
    int64_t last_sync_time = 0;
    const char *device = NULL;
    const char *device_path = "/dev/input";

    /* disable buffering on stdout */
    setbuf(stdout, NULL);

    opterr = 0;
    //这个do{}while(1)循环其实就是用来解析参数的
    do {
        //读取getevent的参数
        c = getopt(argc, argv, "tns:Sv::dpilqc:rh");
        if (c == EOF)
            break;
        switch (c) {
        case 't'://打印时间
            get_time = 1;
            break;
        case 'n':
            newline = "";
            break;
        case 's':
            get_switch = strtoul(optarg, NULL, 0);
            if(dont_block == -1)
                dont_block = 1;
            break;
        case 'S':
            get_switch = ~0;
            if(dont_block == -1)
                dont_block = 1;
            break;
        case 'v':
            if(optarg)
                print_flags |= strtoul(optarg, NULL, 0);
            else
                print_flags |= PRINT_DEVICE | PRINT_DEVICE_NAME | PRINT_DEVICE_INFO | PRINT_VERSION;
            print_flags_set = 1;
            break;
        case 'd':
            print_flags |= PRINT_HID_DESCRIPTOR;
            break;
        case 'p':
            print_flags |= PRINT_DEVICE_ERRORS | PRINT_DEVICE
                    | PRINT_DEVICE_NAME | PRINT_POSSIBLE_EVENTS | PRINT_INPUT_PROPS;
            print_flags_set = 1;
            if(dont_block == -1)
                dont_block = 1;
            break;
        case 'i':
            print_flags |= PRINT_ALL_INFO;
            print_flags_set = 1;
            if(dont_block == -1)
                dont_block = 1;
            break;
        case 'l'://打印事件类型
            print_flags |= PRINT_LABELS;
            break;
        case 'q':
            print_flags_set = 1;
            break;
        case 'c':
            event_count = atoi(optarg);
            dont_block = 0;
            break;
        case 'r'://打印事件的接收速率
            sync_rate = 1;
            break;
        case '?':
            fprintf(stderr, "%s: invalid option -%cn",
                argv[0], optopt);
        case 'h'://打印help的信息
            usage(argv[0]);
            exit(1);
        }
    } while (1);
    if(dont_block == -1)
        dont_block = 0;

    if (optind + 1 == argc) {
        device = argv[optind];
        optind++;
    }
    if (optind != argc) {
        usage(argv[0]);
        exit(1);
    }
    //用来记录监听的事件个数，可以直观的理解为pollfd的数组大小
    nfds = 1;
    //pollfd数组
    ufds = calloc(1, sizeof(ufds[0]));
    //使用intoify监听"/dev/input"路径下的节点变化，如usb,keyboard的热插拔事件
    //这里只是初始化一个fd，还并未开始真正的监听
    ufds[0].fd = inotify_init();
    //监听POLLIN事件
    ufds[0].events = POLLIN;
    //监听具体的某个事件，如getevent /dev/input/event3会进入
    if(device) {
        if(!print_flags_set)
            print_flags |= PRINT_DEVICE_ERRORS;
        res = open_device(device, print_flags);
        if(res < 0) {
            return 1;
        }
    } else {
        if(!print_flags_set)
            print_flags |= PRINT_DEVICE_ERRORS | PRINT_DEVICE | PRINT_DEVICE_NAME;
        print_device = 1;
        //将fd和device_path映射上，该目录下有create或者delete的操作时就会触发POLLIN事件
		res = inotify_add_watch(ufds[0].fd, device_path, IN_DELETE | IN_CREATE);
        if(res < 0) {
            fprintf(stderr, "could not add watch for %s, %sn", device_path, strerror(errno));
            return 1;
        }
        //扫描"/dev/input"路径下的所有事件节点，放入pollfd中
        res = scan_dir(device_path, print_flags);
        if(res < 0) {
            fprintf(stderr, "scan dir failed for %sn", device_path);
            return 1;
        }
    }

    if(get_switch) {
        for(i = 1; i < nfds; i++) {
            uint16_t sw;
            res = ioctl(ufds[i].fd, EVIOCGSW(1), &sw);
            if(res < 0) {
                fprintf(stderr, "could not get switch state, %sn", strerror(errno));
                return 1;
            }
            sw &= get_switch;
            printf("%04x%s", sw, newline);
        }
    }

    if(dont_block)
        return 0;

    while(1) {
        //int pollres =
        //开启监听工作，监听的fd有事件来到的时候唤醒继续往下执行，没有事件的时候阻塞
        poll(ufds, nfds, -1);
        //printf("poll %d, returned %dn", nfds, pollres);
        if(ufds[0].revents & POLLIN) {
            //监听到/dev/input下发生事件
            read_notify(device_path, ufds[0].fd, print_flags);
        }
        //按键，触摸的事件
        for(i = 1; i < nfds; i++) {
            if(ufds[i].revents) {
                if(ufds[i].revents & POLLIN) {
                    res = read(ufds[i].fd, &event, sizeof(event));
                    if(res < (int)sizeof(event)) {
                        fprintf(stderr, "could not get eventn");
                        return 1;
                    }
                    //打印event事件
                    if(get_time) {
                        printf("[%8ld.%06ld] ", event.time.tv_sec, event.time.tv_usec);
                    }
                    //打印event事件名
                    if(print_device)
                        printf("%s: ", device_names[i]);
                    //打印event的type，code，value
                    print_event(event.type, event.code, event.value, print_flags);
                    if(sync_rate && event.type == 0 && event.code == 0) {
                        int64_t now = event.time.tv_sec * 1000000LL + event.time.tv_usec;
                        if(last_sync_time)
                            printf(" rate %lld", 1000000LL / (now - last_sync_time));
                        last_sync_time = now;
                    }
                    printf("%s", newline);
                    if(event_count && --event_count == 0)
                        return 0;
                }
            }
        }
    }

    return 0;
}