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直接上代码。后续再补充分析。

这个是android源码中 getevent 命令的源码。

位于源码的目录：system/core/toolbox/

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?? >>getevent.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/inotify.h>
#include <sys/limits.h>
#include <sys/poll.h>
#include <linux/input.h>
#include <errno.h>

#include "getevent.h"

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

enum {
    PRINT_DEVICE_ERRORS     = 1U << 0,
    PRINT_DEVICE            = 1U << 1,
    PRINT_DEVICE_NAME       = 1U << 2,
    PRINT_DEVICE_INFO       = 1U << 3,
    PRINT_VERSION           = 1U << 4,
    PRINT_POSSIBLE_EVENTS   = 1U << 5,
    PRINT_INPUT_PROPS       = 1U << 6,
    PRINT_HID_DESCRIPTOR    = 1U << 7,

    PRINT_ALL_INFO          = (1U << 8) - 1,

    PRINT_LABELS            = 1U << 16,
};

static const char *get_label(const struct label *labels, int value)
{
    while(labels->name && value != labels->value) {
        labels++;
    }
    return labels->name;
}

static int print_input_props(int fd)
{
    uint8_t bits[INPUT_PROP_CNT / 8];
    int i, j;
    int res;
    int count;
    const char *bit_label;

    printf("  input props:\n");
    res = ioctl(fd, EVIOCGPROP(sizeof(bits)), bits);
    if(res < 0) {
        printf("    <not available\n");
        return 1;
    }
    count = 0;
    for(i = 0; i < res; i++) {
        for(j = 0; j < 8; j++) {
            if (bits[i] & 1 << j) {
                bit_label = get_label(input_prop_labels, i * 8 + j);
                if(bit_label)
                    printf("    %s\n", bit_label);
                else
                    printf("    %04x\n", i * 8 + j);
                count++;
            }
        }
    }
    if (!count)
        printf("    <none>\n");
    return 0;
}

static int print_possible_events(int fd, int print_flags)
{
    uint8_t *bits = NULL;
    ssize_t bits_size = 0;
    const char* label;
    int i, j, k;
    int res, res2;
    struct label* bit_labels;
    const char *bit_label;

    printf("  events:\n");
    for(i = EV_KEY; i <= EV_MAX; i++) { // skip EV_SYN since we cannot query its available codes
        int count = 0;
        while(1) {
            res = ioctl(fd, EVIOCGBIT(i, bits_size), bits);
            if(res < bits_size)
                break;
            bits_size = res + 16;
            bits = realloc(bits, bits_size * 2);
            if(bits == NULL) {
                fprintf(stderr, "failed to allocate buffer of size %d\n", (int)bits_size);
                return 1;
            }
        }
        res2 = 0;
        switch(i) {
            case EV_KEY:
                res2 = ioctl(fd, EVIOCGKEY(res), bits + bits_size);
                label = "KEY";
                bit_labels = key_labels;
                break;
            case EV_REL:
                label = "REL";
                bit_labels = rel_labels;
                break;
            case EV_ABS:
                label = "ABS";
                bit_labels = abs_labels;
                break;
            case EV_MSC:
                label = "MSC";
                bit_labels = msc_labels;
                break;
            case EV_LED:
                res2 = ioctl(fd, EVIOCGLED(res), bits + bits_size);
                label = "LED";
                bit_labels = led_labels;
                break;
            case EV_SND:
                res2 = ioctl(fd, EVIOCGSND(res), bits + bits_size);
                label = "SND";
                bit_labels = snd_labels;
                break;
            case EV_SW:
                res2 = ioctl(fd, EVIOCGSW(bits_size), bits +