这篇文章主要通过分析高通recovery目录下的recovery.cpp源码，对recovery启动流程有一个宏观的了解。

当开机以后，在lk阶段，如果是recovery，会设置boot_into_recovery=1,然后读取recovery.img镜像，把recovery.img的地址和ramdisk等信息作为参数启动kernel，从而进入recovery模式，下面进行简单的分析。

为什么要分析recovery.cpp这个文件？

下面的代码位于bootable/recovery/etc/init.rc，由此可知，进入recovery模式后会执行sbin /recovery，此文件是bootable/recovery/recovery.cpp生成（可查看对应目录的Android.mk查看），所以recovery.cpp是recovery模式的入口。

service recovery /sbin/recovery
    seclabel u:r:recovery:s0

1. 前期准备：

首先列出recovery流程的几个重要点，接着会详细分析

1. 加载recovery.fstab分区表
2. 解析传入的参数
3. recovery界面相关的设置
4. 执行命令
5. 如果没有命令，等待用户输入
6. 结束recovery

bootable/recovery/recovery.cpp



int main(int argc, char **argv) {
    // Take last pmsg contents and rewrite it to the current pmsg session.
    static const char filter[] = "recovery/";
    // Do we need to rotate?
    bool doRotate = false;
    __android_log_pmsg_file_read(
        LOG_ID_SYSTEM, ANDROID_LOG_INFO, filter,
        logbasename, &doRotate);
    //这里的意思暂时不理解
    // Take action to refresh pmsg contents
    __android_log_pmsg_file_read(
        LOG_ID_SYSTEM, ANDROID_LOG_INFO, filter,
        logrotate, &doRotate);

    // If this binary is started with the single argument "--adbd",
    // instead of being the normal recovery binary, it turns into kind
    // of a stripped-down version of adbd that only supports the
    // 'sideload' command.  Note this must be a real argument, not
    // anything in the command file or bootloader control block; the
    // only way recovery should be run with this argument is when it
    // starts a copy of itself from the apply_from_adb() function.
    //如果二进制文件使用单个参数"--adbd"启动
    //而不是正常的recovery启动（不带参数即为正常启动）
    //它变成精简版命令时只支持sideload命令。它必须是一个正确可用的参数
    //不在/cache/recovery/command中，也不受B2B控制
    //是apply_from_adb()的副本


    if (argc == 2 && strcmp(argv[1], "--adbd") == 0) {
        adb_server_main(0, DEFAULT_ADB_PORT, -1);
        return 0;
    }

    time_t start = time(NULL);

    // redirect_stdio should be called only in non-sideload mode. Otherwise
    // we may have two logger instances with different timestamps.
    redirect_stdio(TEMPORARY_LOG_FILE);

    printf("Starting recovery (pid %d) on %s", getpid(), ctime(&start));

    load_volume_table();
    
    //从上面建立的分区表信息中读取是否有cache分区，因为log等重要信息都存在cache分区里

    has_cache = volume_for_path(CACHE_ROOT) != nullptr;
    //从传入的参数或/cache/recovery/command文件中得到相应的命令
    get_args(&argc, &argv);

    const char *send_intent = NULL;
    const char *update_package = NULL;
    bool should_wipe_data = false;
    bool should_wipe_cache = false;
    bool should_wipe_ab = false;
    size_t wipe_package_size = 0;
    bool show_text = false;
    bool sideload = false;
    bool sideload_auto_reboot = false;
    bool just_exit = false;
    bool shutdown_after = false;
    int retry_count = 0;
    bool security_update = false;
    int status = INSTALL_SUCCESS;
    bool mount_required = true;

    int arg;
    int option_index;
    
    
    //while循环解析command或者传入的参数，并把对应的功能设置为true或给相应的变量赋值
    while ((arg = getopt_long(argc, argv, "", OPTIONS, &option_index)) != -1) {
        switch (arg) {
        case 'i': send_intent = optarg; break;
        case 'n': android::base::ParseInt(optarg, &retry_count, 0); break;
        case 'u': update_package = optarg; break;
        case 'w': should_wipe_data = true; break;
        case 'c': should_wipe_cache = true; break;
        case 't': show_text = true; break;
        case 's': sideload = true; break;
        case 'a': sideload = true; sideload_auto_reboot = true; break;
        cas