Add option to automatically unmount system before installing ZIP

This adds the option to automatically unmount the system partition
before installing a ZIP-file.
This option is enabled by default, This is usefull on SAR-devices
where system is mounted as system_root and ZIPs (i.e. Magisk)
try to unmount system instead of system_root and fail to install.

Change-Id: Id94ae658964679e23aa7fa137e07edf74ee073df

twinstall.cpp

@@ -339,7 +339,7 @@ static int Run_Update_Binary(const char *path, ZipWrap *Zip, int* wipe_cache, zi
 }
 
 int TWinstall_zip(const char* path, int* wipe_cache) {
-	int ret_val, zip_verify = 1;
+	int ret_val, zip_verify = 1, unmount_system = 1;
 
 	if (strcmp(path, "error") == 0) {
 		LOGERR("Failed to get adb sideload file: '%s'\n", path);
@@ -359,6 +359,8 @@ int TWinstall_zip(const char* path, int* wipe_cache) {
 		}
 	}
 
+	DataManager::GetValue(TW_UNMOUNT_SYSTEM, unmount_system);
+
 #ifndef TW_OEM_BUILD
 	DataManager::GetValue(TW_SIGNED_ZIP_VERIFY_VAR, zip_verify);
 #endif
@@ -410,6 +412,14 @@ int TWinstall_zip(const char* path, int* wipe_cache) {
 		return INSTALL_CORRUPT;
 	}
 
+	if (unmount_system) {
+		gui_msg("unmount_system=Unmounting System...");
+		if(!PartitionManager.UnMount_By_Path(PartitionManager.Get_Android_Root_Path(), true)) {
+			gui_err("unmount_system_err=Failed unmounting System");
+			return -1;
+		}
+	}
+
 	time_t start, stop;
 	time(&start);
 	if (Zip.EntryExists(ASSUMED_UPDATE_BINARY_NAME)) {