第三方应用放在/system/preloadapp/下，开机不会自动安装问题解决

Android P版本。
解决方案如下：

diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index 4f09f6e..e6f2f19 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -2652,6 +2652,14 @@ public class PackageManagerService extends IPackageManager.Stub
                     | SCAN_AS_SYSTEM,
                     0);
 
+            final File preloadAppDir = new File(Environment.getRootDirectory(), "preloadapp");
+            scanDirTracedLI(preloadAppDir,
+                    mDefParseFlags
+                    | PackageParser.PARSE_IS_SYSTEM_DIR,
+                    scanFlags
+                    | SCAN_AS_SYSTEM,
+                    0);
+
             // Collect privileged vendor packages.
             File privilegedVendorAppDir = new File(Environment.getVendorDirectory(), "priv-app");

测试如下：将ES文件管理器放到下面目录，上面代码修改之后，m services后替换services各组件，然后重启服务，之后能看到launcher中存在ES文件管理器，且能正常使用。
/system/preloadapp/cs/es-file-explorer-4-2-6-2-1.apk

替换services各组件命令：
adb root
adb remount
adb push X:\system\framework\oat\arm64\services.vdex /system/framework/oat/arm64/
adb push X:\system\framework\oat\arm64\services.odex /system/framework/oat/arm64/
adb push X:\system\framework\oat\arm64\services.art /system/framework/oat/arm64/
adb push X:\system\framework\services.jar.prof /system/framework/
adb push X:\system\framework\services.jar /system/framework/
adb shell sync
adb shell stop
adb shell start