Iot_Cs_best/init.c

/*
 * Copyright (c) 2013-2019 Huawei Technologies Co., Ltd. All rights reserved.
 * Copyright (c) 2020-2021 Huawei Device Co., Ltd. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of
 *    conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list
 *    of conditions and the following disclaimer in the documentation and/or other materials
 *    provided with the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its contributors may be used
 *    to endorse or promote products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/wait.h>

#ifdef LOSCFG_QUICK_START
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <sys/ioctl.h>

#define QUICKSTART_IOC_MAGIC    'T'
#define QUICKSTART_INITSTEP2    _IO(QUICKSTART_IOC_MAGIC, 0)
#define WAIT_FOR_SAMPLE         300000  // wait 300ms for sample
#endif
int main(int argc, char * const *argv)
{
    (void)argv; 
    int ret;  // 声明一个整数变量ret，用于存储函数的返回值
    pid_t gid;  // 声明一个pid_t类型的变量gid，用于存储进程组ID  
    const char *shellPath = "/bin/mksh";// 定义一个字符串常量shellPath，存储shell的路径，这里使用的是mksh shell
 // 以下部分是一个条件编译块，如果定义了LOSCFG_QUICK_START宏，这段代码会被编译进程序  
#ifdef LOSCFG_QUICK_START
    const char *samplePath = "/dev/shm/sample_quickstart";// 定义一个字符串常量samplePath，存储sample_quickstart的路径  
	// 使用fork函数创建子进程，返回值存储在ret变量中  
    // 如果ret小于0，说明创建子进程失败；如果ret等于0，说明这是子进程；如果ret大于0，说明这是父进程，ret是子进程的ID  
    ret = fork();
    if (ret < 0) { // 如果创建子进程失败，输出错误消息  
        printf("Failed to fork for sample_quickstart\n");
    } else if (ret == 0) {// 如果是子进程，获取进程组ID并存储在gid变量中，如果获取失败，输出错误消息并退出  
        (void)execve(samplePath, NULL, NULL);
        exit(0);
    }

    usleep(WAIT_FOR_SAMPLE);

    int fd = open("/dev/quickstart", O_RDONLY);
    if (fd != -1) {
        ioctl(fd, QUICKSTART_INITSTEP2);
        close(fd);
    }
#endif
    ret = fork();
    if (ret < 0) {
        printf("Failed to fork for shell\n");
    } else if (ret == 0) {
        gid = getpgrp();
        if (gid < 0) {
            printf("get group id failed, pgrpid %d, errno %d\n", gid, errno);
            exit(0);
        }
        ret = tcsetpgrp(STDIN_FILENO, gid);
        if (ret != 0) {// 如果是子进程，尝试将STDIN（标准输入）重定向到指定的进程组（通过tcsetpgrp函数实现），如果重定向失败，输出错误消息并退出 
            printf("tcsetpgrp failed, errno %d\n", errno);
            exit(0);
        }
         // 如果是子进程，使用execve函数执行shellPath指定的shell程序，参数为NULL，环境变量为NULL  
        (void)execve(shellPath, NULL, NULL);
        exit(0);
    }

    while (1) {  // 如果是父进程，进入一个无限循环，不断地调用waitpid函数等待子进程的状态变化（通过WNOHANG标志实现）  
        ret = waitpid(-1, 0, WNOHANG);            // 如果子进程还在运行，等待1秒后再次检查；如果子进程已经停止运行，继续等待下一次检查（通过waitpid函数实现）  
        if (ret == 0) {
            sleep(1);
        }
    };
}