[Android][Recovery] Recovery下找不到sdcard路径

做升级的时候，把更新包拷贝到sd卡中，然后调用接口进行重启升级

File update_file = new File("/sdcard/update.zip");
try {
    Log.d("WOW", "install " + update_file.getAbsolutePath());
    RecoverySystem.installPackage(getBaseContext(), update_file);
} catch (IOException e) {
    e.printStackTrace();
}

之后进入Recovery模式后报错：

Supported API: 3
charge_status 3, charged 0, status 0, capacity 62
Finding update package...
Opening update package...
E:unknow volume for path [/storage/emulated/0/update.zip]
E:failed to map file
Installation aborted.

说是找不到/storage/emulated/0这个路径？

因为上层用Java写路径的时候，获取的是Android的路径，我们知道，adb shell里面是有/sdcard的路径的，这个路径实际上并不是插入的SD卡路径，而是一个内置路径。

内置路径通过 ls -l 可以看到 /sdcard 的映射
lrwxrwxrwx 1 root root 21 1970-01-01 08:00 sdcard -> /storage/self/primary
也就是说下面几个路径是一样的
/sdcard/
/storage/emulated/0
/storage/self/primary

而外置sd卡路径是
/storage/0658-0900

所以，我们代码里写的是/sdcard但是传到Recovery的路径就变成/storage/emulated/0了。

我们的需求是把升级包放到sdcard里面去，所以就需要修改Recovery里的文件路径。

实际要做的就是把获得到的路径里面/storage/emulated/0替换成/sdcard即可：

Recovery里面的sd卡路径就是/sdcard/

    if (update_package) {
        // For backwards compatibility on the cache partition only, if
        // we're given an old 'root' path "CACHE:foo", change it to
        // "/cache/foo".
        if (strncmp(update_package, "CACHE:", 6) == 0) {
            int len = strlen(update_package) + 10;
            char* modified_path = (char*)malloc(len);
            if (modified_path) {
                strlcpy(modified_path, "/cache/", len);
                strlcat(modified_path, update_package+6, len);
                printf("(replacing path \"%s\" with \"%s\")\n",
                       update_package, modified_path);
                update_package = modified_path;
            }
            else
                printf("modified_path allocation failed\n");
        } else if(strncmp(update_package, "/storage/emulated/0/", 20) == 0) {
            int len = strlen(update_package) + 20;
            char* modified_path = (char*)malloc(len);
            if (modified_path) {
                strlcpy(modified_path, "/sdcard/", len);
                strlcat(modified_path, update_package+20, len);
                printf("(replacing path \"%s\" with \"%s\")\n",
                       update_package, modified_path);
                update_package = modified_path;
            }
            else
                printf("modified_path allocation failed\n");
        }

Ref https://blog.csdn.net/wed110/article/details/9943915?utm_source=blogxgwz1