android7.1 外置SD卡三方应用没有读写权限

车机上面会挂载SD卡和U盘，三方应用想要在外置存储中读写文件操作需要添加权限，系统修改如下：

/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java

commit a25497c19f5eef9d0d113710492f7d66dbbb9702
Author: zhoujinyan
Date:   Mon May 18 14:52:25 2020 +0800

    [frameworks]解决三方应用没有权限读写sd问题
diff --git a/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java b/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
index 66615a0..3f1f844 100755
--- a/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -10177,7 +10177,8 @@ public class PackageManagerService extends IPackageManager.Stub {
                 case PermissionInfo.PROTECTION_SIGNATURE: {
                     // For all apps signature permissions are install time ones.
                     allowedSig = grantSignaturePermission(perm, pkg, bp, origPermissions);
-                    if (allowedSig) {
+                   //对所有应用放开android.permission.WRITE_MEDIA_STORAGE权限.add by zhoujinyan 20200518
+                    if (allowedSig || perm.equals("android.permission.WRITE_MEDIA_STORAGE")) {
                         grant = GRANT_INSTALL;
                     }
                 } break;