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

做升級的時候，把更新包拷貝到sd卡中，然后調用接口進行重啟升級
wossoneri.github.io

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();
}

之后進入Recovery模式后報錯：

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.

說是找不到/storage/emulated/0這個路徑？

因為上層用Java寫路徑的時候，獲取的是Android的路徑，我們知道，adb shell里面是有/sdcard的路徑的，這個路徑實際上並不是插入的SD卡路徑，而是一個內置路徑。

內置路徑通過 ls -l 可以看到 /sdcard 的映射
lrwxrwxrwx 1 root root 21 1970-01-01 08:00 sdcard -> /storage/self/primary
也就是說下面幾個路徑是一樣的
/sdcard/
/storage/emulated/0
/storage/self/primary

而外置sd卡路徑是
/storage/0658-0900

所以，我們代碼里寫的是/sdcard但是傳到Recovery的路徑就變成/storage/emulated/0了。

我們的需求是把升級包放到sdcard里面去，所以就需要修改Recovery里的文件路徑。

實際要做的就是把獲得到的路徑里面/storage/emulated/0替換成/sdcard即可：

Recovery里面的sd卡路徑就是/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