C++ WINAPI Create Multiple Partitions on Mounted VHD

Question

I managed to create a VHD and attached it. Afterwards, I created a disk(IOCTL CREATE_DISK) and set its layout using IOCTL_DISK_SET_DRIVE_LAYOUT_EX. Now, when I examine disk through Disk Management. I have a 14MB with a 7 MB partition, expectedly.

int sign = 80001;
CREATE_DISK disk;
disk.Mbr.Signature = sign;
disk.PartitionStyle = PARTITION_STYLE_MBR;

auto res = DeviceIoControl(device_handle, IOCTL_DISK_CREATE_DISK, &disk, sizeof(disk), NULL, 0, NULL, NULL);
res = DeviceIoControl(device_handle, IOCTL_DISK_UPDATE_PROPERTIES, 0, 0, NULL, 0, NULL, NULL);

LARGE_INTEGER partition_size;
partition_size.QuadPart = 0xF00;
DWORD driver_layout_ex_len = sizeof(DRIVE_LAYOUT_INFORMATION_EX);
DRIVE_LAYOUT_INFORMATION_EX driver_layout_info;
memset(&driver_layout_info, 0, sizeof(DRIVE_LAYOUT_INFORMATION_EX));

driver_layout_info.Mbr.Signature = sign;
driver_layout_info.PartitionCount = 1;
driver_layout_info.PartitionStyle = PARTITION_STYLE_MBR;

PARTITION_INFORMATION_EX part_info;
PARTITION_INFORMATION_MBR mbr_info;
part_info.StartingOffset.QuadPart = 32256;
part_info.RewritePartition = TRUE;
part_info.PartitionLength.QuadPart = partition_size.QuadPart/2 * 4096;
part_info.PartitionNumber = 1;
part_info.PartitionStyle = PARTITION_STYLE_MBR;

mbr_info.BootIndicator = TRUE;
mbr_info.HiddenSectors = 32256 / 512;
mbr_info.PartitionType = PARTITION_FAT32;
mbr_info.RecognizedPartition = 1;
part_info.Mbr = mbr_info;
driver_layout_info.PartitionEntry[0] = part_info;
auto res_layout = DeviceIoControl(device_handle, IOCTL_DISK_SET_DRIVE_LAYOUT_EX, &driver_layout_info, sizeof(driver_layout_info), NULL, 0, NULL, NULL);

Now, how do I partitionize this disk into two partitions? I want to create another partition out of the unpartitioned part of the disk(the other half basically). It says in the documentation is that PartitionEntry is an array of variable size(No, it is not it is an array of size 1.) Do I call set layout IOCTL for every partition I want to create? If so, how do you go about that? Is multi-partitioning possible through WINAPI interface?

P.S: I am aware that people usually invoke diskpart for this line of work.

Edit: Adding second partition two layout was messing my stack up so I took another route (heap).

DWORD driver_layout_ex_len = sizeof(DRIVE_LAYOUT_INFORMATION_EX) + sizeof(PARTITION_INFORMATION_EX); // one layout+partition + partition
PDRIVE_LAYOUT_INFORMATION_EX driver_layout_info = (PDRIVE_LAYOUT_INFORMATION_EX) std::calloc(1, driver_layout_ex_len);

driver_layout_info->Mbr.Signature = sign;
driver_layout_info->PartitionCount = 2;
driver_layout_info->PartitionStyle = PARTITION_STYLE_MBR;
// omitted here..
PARTITION_INFORMATION_EX part_info2;
part_info2.StartingOffset.QuadPart = 32256 + part_info.PartitionLength.QuadPart;
part_info2.RewritePartition = TRUE;
part_info2.PartitionLength.QuadPart = partition_size.QuadPart / 2 * 4096;
part_info2.PartitionNumber = 2;
part_info2.PartitionStyle = PARTITION_STYLE_MBR;

part_info2.Mbr = mbr_info;


driver_layout_info->PartitionEntry[0] = part_info;
driver_layout_info->PartitionEntry[1] = part_info2;
auto res_layout = DeviceIoControl(device_handle, IOCTL_DISK_SET_DRIVE_LAYOUT_EX, driver_layout_info, driver_layout_ex_len, NULL, 0, NULL, NULL);
auto res_err = GetLastError(); 

Since it was overriding my device_handle I could not IOCTL at all. This improvement eliminated that. Do not forget to pass driver_layout_info instead of &driver_layout_info after this change.

Answer 1

It says in the documentation is that PartitionEntry is an array of variable size(No, it is not it is an array of size 1.)

"Some Windows structures are variable-sized, beginning with a fixed header, followed by a variable-sized array. When these structures are declared, they often declare an array of size 1 where the variable-sized array should be." Refer to @Raymond blog.

Here DRIVE_LAYOUT_INFORMATION_EX structure is an example:

typedef struct _DRIVE_LAYOUT_INFORMATION_EX {
  DWORD                    PartitionStyle;
  DWORD                    PartitionCount;
  union {
    DRIVE_LAYOUT_INFORMATION_MBR Mbr;
    DRIVE_LAYOUT_INFORMATION_GPT Gpt;
  } DUMMYUNIONNAME;
  PARTITION_INFORMATION_EX PartitionEntry[1];
} DRIVE_LAYOUT_INFORMATION_EX, *PDRIVE_LAYOUT_INFORMATION_EX;

With this declaration, you would allocate memory for one such variable-sized DRIVE_LAYOUT_INFORMATION_EX structure like this:

PDRIVE_LAYOUT_INFORMATION_EX driver_layout_info = (PDRIVE_LAYOUT_INFORMATION_EX)malloc(FIELD_OFFSET(DRIVE_LAYOUT_INFORMATION_EX, PartitionEntry[NumberOfPartitions]));

You would initialize the structure like this (Use 2 partitions as example):

DWORD NumberOfPartitions = 2;
LARGE_INTEGER partition_size;
partition_size.QuadPart = 0xF00;

PARTITION_INFORMATION_MBR mbr_info;
mbr_info.BootIndicator = TRUE;
mbr_info.HiddenSectors = 32256 / 512;
mbr_info.PartitionType = PARTITION_FAT32;
mbr_info.RecognizedPartition = TRUE;

PDRIVE_LAYOUT_INFORMATION_EX driver_layout_info = (PDRIVE_LAYOUT_INFORMATION_EX)malloc(FIELD_OFFSET(DRIVE_LAYOUT_INFORMATION_EX, PartitionEntry[NumberOfPartitions]));
for (DWORD Index = 0; Index < NumberOfPartitions ; Index++) {

    driver_layout_info->PartitionEntry[Index].PartitionStyle = PARTITION_STYLE_MBR;
    driver_layout_info->PartitionEntry[Index].PartitionNumber = Index + 1;
    driver_layout_info->PartitionEntry[Index].RewritePartition = TRUE;
    driver_layout_info->PartitionEntry[Index].PartitionLength.QuadPart = partition_size.QuadPart / 2 * 4096;
    driver_layout_info->PartitionEntry[Index].Mbr = mbr_info;
}

driver_layout_info->Mbr.Signature = sign;
driver_layout_info->PartitionCount = 1;
driver_layout_info->PartitionStyle = PARTITION_STYLE_MBR;

driver_layout_info->PartitionEntry[0].StartingOffset.QuadPart = 32256;
driver_layout_info->PartitionEntry[1].StartingOffset.QuadPart = 32256 + driver_layout_info->PartitionEntry->StartingOffset.QuadPart;

DWORD driver_layout_ex_len = sizeof(DRIVE_LAYOUT_INFORMATION_EX) + sizeof(PARTITION_INFORMATION_EX);

Call free(driver_layout_info); after you use completely.