android P系统WRITE_MEDIA_STORAGE添加

由于android P 版本google把android.Permission.WRITE_MEDIA_STORAGE中sd卡的读写权限移除了，导致系统文件管理中的文件无法直接复制到SD卡，所以需要把SD卡的读写权限加上到WRITE_MEDIA_STORAGE权限中去，
方法一、
1、frameworks\base\data\etc\platform.xml中添加：

<permission name="android.permission.WRITE_MEDIA_STORAGE" >
        <group gid="media_rw" />
    <group gid="sdcard_rw" />   <!-- add this -->
    </permission>

2、frameworks\base\services\core\java\com\android\server\pm\PackageManagerService.java

...
public int getMountMode(int uid, String packageName) {
                if (Process.isIsolated(uid)) {
                    return Zygote.MOUNT_EXTERNAL_NONE;
                }
                //   modify android.Permission.WRITE_MEDIA_STORAGE add sdcard_rw permission start
                if (checkUidPermission(WRITE_MEDIA_STORAGE, uid) == PERMISSION_GRANTED) {
                    return Zygote.MOUNT_EXTERNAL_DEFAULT;
                }
                // momdify end
                if (checkUidPermission(READ_EXTERNAL_STORAGE, uid) == PERMISSION_DENIED) {
                    return Zygote.MOUNT_EXTERNAL_DEFAULT;
                }
                if (checkUidPermission(WRITE_EXTERNAL_STORAGE, uid) == PERMISSION_DENIED) {
                    return Zygote.MOUNT_EXTERNAL_READ;
                }
                return Zygote.MOUNT_EXTERNAL_WRITE;
            }
...

方法二、修改system\vold\model\PublicVolume.cpp

...
if (getMountFlags() & MountFlags::kPrimary) {
            if (execl(kFusePath, kFusePath,
                    "-u", "1023", // AID_MEDIA_RW
                    "-g", "1023", // AID_MEDIA_RW
                    "-U", std::to_string(getMountUserId()).c_str(),
                    "-w",
                    mRawPath.c_str(),
                    stableName.c_str(),
                    NULL)) {
                PLOG(ERROR) << "Failed to exec";
            }
        } else {
            if (execl(kFusePath, kFusePath,
                    "-u", "1023", // AID_MEDIA_RW
                    "-g", "1023", // AID_MEDIA_RW
                    "-U", std::to_string(getMountUserId()).c_str(),
                    "-w", // add this
                    mRawPath.c_str(),
                    stableName.c_str(),
                    NULL)) {
                PLOG(ERROR) << "Failed to exec";
            }
        }

参考：
https://blog.csdn.net/ch853199769/article/details/88052886
https://blog.csdn.net/qq_27061049/article/details/93715885