partition: add support dm_use_original_path

* On some mediatek devices we must use symlinked path instead of the
      real block device.  Needed for decryption on some MTK HW FDE devices.

Change-Id: Ib48d745fd442c590aea2baf6d2dbe20aaaef9eec

partition.cpp

@@ -161,6 +161,7 @@ enum TW_FSTAB_FLAGS {
 	TWFLAG_KEYDIRECTORY,
 	TWFLAG_WRAPPEDKEY,
 	TWFLAG_ADOPTED_MOUNT_DELAY,
+	TWFLAG_DM_USE_ORIGINAL_PATH,
 };
 
 /* Flags without a trailing '=' are considered dual format flags and can be
@@ -206,6 +207,7 @@ const struct flag_list tw_flags[] = {
 	{ "keydirectory=",          TWFLAG_KEYDIRECTORY },
 	{ "wrappedkey",             TWFLAG_WRAPPEDKEY },
 	{ "adopted_mount_delay=",   TWFLAG_ADOPTED_MOUNT_DELAY },
+	{ "dm_use_original_path",   TWFLAG_DM_USE_ORIGINAL_PATH },
 	{ 0,                        0 },
 };
 
@@ -271,6 +273,8 @@ TWPartition::TWPartition() {
 	Key_Directory = "";
 	Is_Super = false;
 	Adopted_Mount_Delay = 0;
+	Original_Path = "";
+	Use_Original_Path = false;
 }
 
 TWPartition::~TWPartition(void) {
@@ -670,7 +674,7 @@ void TWPartition::Setup_Data_Partition(bool Display_Error) {
 	} else if (!Mount(false)) {
 		if (Is_Present) {
 			if (Key_Directory.empty()) {
-				set_partition_data(Actual_Block_Device.c_str(), Crypto_Key_Location.c_str(),
+				set_partition_data(Use_Original_Path ? Original_Path.c_str() : Actual_Block_Device.c_str(), Crypto_Key_Location.c_str(),
 				Fstab_File_System.c_str());
 				if (cryptfs_check_footer() == 0) {
 					Is_Encrypted = true;
@@ -1015,6 +1019,9 @@ void TWPartition::Apply_TW_Flag(const unsigned flag, const char* str, const bool
 		case TWFLAG_KEYDIRECTORY:
 			Key_Directory = str;
 			break;
+		case TWFLAG_DM_USE_ORIGINAL_PATH:
+			Use_Original_Path = true;
+			break;
 		default:
 			// Should not get here
 			LOGINFO("Flag identified for processing, but later unmatched: %i\n", flag);
@@ -1227,6 +1234,8 @@ void TWPartition::Setup_Data_Media() {
 void TWPartition::Find_Real_Block_Device(string& Block, bool Display_Error) {
 	char device[PATH_MAX], realDevice[PATH_MAX];
 
+	Original_Path = Block;
+
 	strcpy(device, Block.c_str());
 	memset(realDevice, 0, sizeof(realDevice));
 	while (readlink(device, realDevice, sizeof(realDevice)) > 0)