Mapping VolumeID to Disk partition Using the DeviceIOControl API

Article
03/19/2010

To map a volume with drive letter to disk partition, one may use some combination of WMI classes like

Win32_LogicalDisk,Win32_LogicalDiskToPartition,Win32_DiskPartition, Win32_DiskDriveToDiskPartition and Win32_DiskDrive.

Unfortunately WMI does not provide a way to map a disk partition that does not have a drive letter associated with it. There is no WMI class to associate a disk volume to disk partition directly. However, one can use the low level DeviceIoControl API to request disk partition information directly from the disk device driver.

Below is a sample program to list all the volumeIDs with corresponding partitions and steps to build the sample using WDK.

1) Download and install the WDK from www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=36a2630f-5d56-43b5-b996-7633f2ec14ff

2) Start a command prompt and go to the bin directory in WinDDK installtion folder and run setenv.bat for whatever system you are building for, for example:

setenv C:\WinDDK\7268.0.0 chk WNET

3) At this point you have a build environment pointing to the WDK install folders created within the CMD window.

4) Create a folder named 'mounts' in the build environment folder created in step 3 (in this example C:\WinDDK\7268.0.0) and create following files in it

* A Header file named 'enumvol.h' using the code snippet given below under enumvol.h header

* A 'C' source file named 'mounts.c' using code snippet given below under 'mounts.c'header

* A 'MakeFile' file named 'MakeFile'using the text given under header 'MakeFile' header

* A 'Source' file named 'Source'using the text given under 'Source'header

5) Navigate to the folder created in step 4 and run “bcz”, this will create an executable file that will display the disk partition information.

Source Files

================

'===================================================================
' DISCLAIMER:
'-------------------------------------------------------------------
'
' This sample is provided as is and is not meant for use on a
' production environment. It is provided only for illustrative
' purposes. The end user must test and modify the sample to suit
' their target environment.
'
' Microsoft can make no representation concerning the content of
' this sample. Microsoft is providing this information only as a
' convenience to you. This is to inform you that Microsoft has not
' tested the sample and therefore cannot make any representations
' regarding the quality, safety, or suitability of any code or
' information found here.
'
'===================================================================

/**************************************************enumvol.h************************************************/

#ifndef _ENUMVOL_H_

#define _ENUMVOL_H_

// Command Descriptor Block constants.

#define CDB6GENERIC_LENGTH 6

#define CDB10GENERIC_LENGTH 10

#define SCSIOP_INQUIRY 0x12

#define BUF_LEN (8*1024)

#define DIRECT_ACCESS_DEVICE 0

// Define constants for \DosDevices\X:

#define DOSDEVICES_LENGTH 12

#define DRIVE_LETTER_LENGTH 14

#define DRIVE_LETTER_POSITION 12

#define DRIVE_COLON_POSITION 13

#define MOUNTMGR_NAME "\\\\.\\MountPointManager"

// Bus Type

static char* BusType[] = {

"UNKNOWN", // 0x00

"SCSI",

"ATAPI",

"ATA",

"IEEE 1394",

"SSA",

"FIBRE",

"USB",

"RAID"

};

// SCSI Device Type

static char* DeviceType[] = {

"Direct Access Device", // 0x00

"Tape Device", // 0x01

"Printer Device", // 0x02

"Processor Device", // 0x03

"WORM Device", // 0x04

"CDROM Device", // 0x05

"Scanner Device", // 0x06

"Optical Disk", // 0x07

"Media Changer", // 0x08

"Comm. Device", // 0x09

"ASCIT8", // 0x0A

"ASCIT8", // 0x0B

"Array Device", // 0x0C

"Enclosure Device", // 0x0D

"RBC Device", // 0x0E

"Unknown Device" // 0x0F

};

typedef struct _SCSI_PASS_THROUGH_WITH_BUFFERS {

SCSI_PASS_THROUGH Spt;

ULONG Filler; // realign buffers to double word boundary

UCHAR SenseBuf[32];

UCHAR DataBuf[512];

} SCSI_PASS_THROUGH_WITH_BUFFERS, *PSCSI_PASS_THROUGH_WITH_BUFFERS;

VOID PrintError( ULONG );

BOOL GetDeviceProperty( HDEVINFO, DWORD );

VOID DebugPrint( USHORT, PCHAR, ... );

void PrintMountName(PMOUNTDEV_NAME mountName);

void PrintName(PWCHAR Name, USHORT Len);

void GetDriveLetter(PMOUNTDEV_NAME mountName);

void GetVolumeExtents(PWCHAR volumeGuid);

BOOL IsDriveLetter(PWCHAR Name, USHORT Len);

BOOL IsVolumeGuid(PWCHAR Name, USHORT Len);

#endif // _ENUMVOL_H_

/**************************************************enumvol.h************************************************/

/**************************************************mounts.c*************************************************/

#include <stdio.h>

#include <stdlib.h>

#include <stddef.h>

#include <windows.h>

#include <initguid.h> // Guid definition

#include <devguid.h> // Device guids

#include <setupapi.h> // for SetupDiXxx functions.

#include <cfgmgr32.h> // for SetupDiXxx functions.

#include <devioctl.h>

#include <ntdddisk.h>

#include <ntddvol.h>

#include <ntddscsi.h>

#include <mountdev.h>

#include <mountmgr.h>

#include <enumvol.h>

BOOL GetStorageDeviceNumber(HANDLE device, PSTORAGE_DEVICE_NUMBER number)

{

BOOL status;

unsigned long returned_bytes;

//unsigned long returned_bytes, errno;

status = DeviceIoControl(device,

IOCTL_STORAGE_GET_DEVICE_NUMBER,

NULL,

number,

sizeof(STORAGE_DEVICE_NUMBER),

&returned_bytes,

FALSE);

if (!status) {

errno = GetLastError();

//printf("Error getting storage device number: status %d, returned %d\n", errno, returned_bytes);

return FALSE;

} else {

//printf("got storage device number: disk%d, part%d\n",

// number->DeviceNumber, number->PartitionNumber);

}

return TRUE;

}

BOOL GetPartitionInfoEx(HANDLE device, PPARTITION_INFORMATION_EX PartInfo)

{

BOOL status;

unsigned long returned_bytes;

//unsigned long returned_bytes, errno;

status = DeviceIoControl(device,

IOCTL_DISK_GET_PARTITION_INFO_EX,

NULL,

PartInfo,

sizeof(PARTITION_INFORMATION_EX),

&returned_bytes,

FALSE);

if (!status) {

errno = GetLastError();

//printf("Error getting partition info: status %d, returned %d\n", errno, returned_bytes);

return FALSE;

} else {

//printf("got partition info: offset %I64x, length %I64x\n", PartInfo->StartingOffset, PartInfo->PartitionLength);

}

return TRUE;

}

BOOL GetPartitionInfo(HANDLE device, PPARTITION_INFORMATION PartInfo)

{

BOOL status;

unsigned long returned_bytes;

//unsigned long returned_bytes, errno;

status = DeviceIoControl(device,

IOCTL_DISK_GET_PARTITION_INFO,

NULL,

PartInfo,

sizeof(PARTITION_INFORMATION),

&returned_bytes,

FALSE);

if (!status) {

errno = GetLastError();

//printf("Error getting partition info: status %d, returned %d\n", errno, returned_bytes);

return FALSE;

} else {

//printf("got partition info: offset %I64x, length %I64x\n", PartInfo->StartingOffset, PartInfo->PartitionLength);

}

return TRUE;

}

ULONG DebugLevel = 1;

// 0 = Suppress All Messages

// 1 = Display & Fatal Error Message

// 2 = Warning & Debug Messages

// 3 = Informational Messages

BOOL IsFixedDisk;

WCHAR FoundDevice[256];

BOOL found = FALSE;

VOID DebugPrint( USHORT DebugPrintLevel, PCHAR DebugMessage, ... )

/*++

Routine Description:

This routine print the given string, if given debug level is <= to the

current debug level.

Arguments:

DebugPrintLevel - Debug level of the given message

DebugMessage - Message to be printed

--*/

{

va_list args;

va_start(args, DebugMessage);

if (DebugPrintLevel <= DebugLevel) {

char buffer[128];

(VOID) vsprintf(buffer, DebugMessage, args);

printf( "%s", buffer );

}

va_end(args);

}

/*++

Routine Description:

This function prints the given Unicode string.

Arguments:

WCHAR string and length

--*/

void PrintName(PWCHAR Name, USHORT Len)

{

SHORT i;

for ( i = 0; i < (Len) ; i++ ) {

printf("%C", Name[i]);

}

void GetMounts()

{

DWORD bytesReturned;

UCHAR Bytes[10000];

PMOUNTMGR_MOUNT_POINTS pMntPoints = (PMOUNTMGR_MOUNT_POINTS) Bytes;

MOUNTMGR_MOUNT_POINT mntPoint, *pmnt;

DWORD err = 0;

HANDLE h;

ULONG index;

WCHAR symbolicName[MAX_PATH], deviceName[MAX_PATH], uniqueId[MAX_PATH];

h = CreateFile("\\\\.\\MountPointManager",

GENERIC_READ,

FILE_SHARE_READ | FILE_SHARE_WRITE,

NULL,

OPEN_EXISTING,

NULL);

if (h == INVALID_HANDLE_VALUE) {

err = GetLastError();

printf("can't open: %d\n", err);

return;

}

ZeroMemory(pMntPoints, 10000);

ZeroMemory(&mntPoint, sizeof(MOUNTMGR_MOUNT_POINT));

pMntPoints->Size = 10000;

if(DeviceIoControl(h,

IOCTL_MOUNTMGR_QUERY_POINTS,

&mntPoint,

sizeof(MOUNTMGR_MOUNT_POINT),

pMntPoints,

10000,

&bytesReturned,

NULL)) {

if(bytesReturned && pMntPoints->Size && pMntPoints->NumberOfMountPoints) {

for(index = 0; index < pMntPoints->NumberOfMountPoints; index++) {

pmnt = &pMntPoints->MountPoints[index];

ZeroMemory(symbolicName, MAX_PATH);

ZeroMemory(deviceName, MAX_PATH);

ZeroMemory(uniqueId, MAX_PATH);

wcsncpy(symbolicName, (PWCHAR) &Bytes[pmnt->SymbolicLinkNameOffset], pmnt->SymbolicLinkNameLength/sizeof(WCHAR));

wcsncpy(uniqueId, (PWCHAR) &Bytes[pmnt->UniqueIdOffset], pmnt->UniqueIdLength/sizeof(WCHAR));

wcsncpy(deviceName, (PWCHAR) &Bytes[pmnt->DeviceNameOffset], pmnt->DeviceNameLength/sizeof(WCHAR));

//if (IsVolumeGuid(symbolicName, pmnt->SymbolicLinkNameLength/sizeof(WCHAR))) {

printf("%d) %ws => %ws\n", index, symbolicName, deviceName);

//}

//printf("%d) %ws => %ws\n", index, symbolicName, deviceName);

}

} else {

err = GetLastError();

}

CloseHandle(h);

printf("err=%d ret=%d\n", err, bytesReturned);

}

int __cdecl main()

/*++

Routine Description:

This is the main function. It takes no arguments from the user.

Arguments:

None

Return Value:

Status

--*/

{

HDEVINFO hIntDevInfo;

DWORD index;

BOOL status;

// Open the device using device interface registered by the driver

found = FALSE;

// Get the interface device information set that contains all devices of event class.

hIntDevInfo = SetupDiGetClassDevs (

(LPGUID) &VolumeClassGuid, //&GUID_DEVCLASS_VOLUMESNAPSHOT, //&MOUNTDEV_MOUNTED_DEVICE_GUID, //

NULL, // Enumerator

NULL, // Parent Window

(DIGCF_PRESENT | DIGCF_INTERFACEDEVICE // Only Devices present & Interface class

));

if( hIntDevInfo == INVALID_HANDLE_VALUE ) {

DebugPrint( 1, "SetupDiGetClassDevs failed with error: %d\n", GetLastError() );

exit(1);

}

// Enumerate all the disk devices

index = 0;

while (TRUE) {

status = GetDeviceProperty( hIntDevInfo, index );

if ( status == FALSE ) {

break;

}

index++;

}

SetupDiDestroyDeviceInfoList(hIntDevInfo);

return 0;

}

#define MAX_COMP_INSTID 2096

#define MAX_COMP_DESC 2096

#define MAX_FRIENDLY 2096

BOOL GetDeviceProperty(HDEVINFO IntDevInfo, DWORD Index )

/*++

Routine Description:

This routine enumerates the volumes using the Device interface

GUID VolumeClassGuid. Gets the Adapter & Device property from the port

driver. Get the mount name, SCSI address and locks the volume for exclusive

access, if possible.

Arguments:

IntDevInfo - Handles to the interface device information list

Index - Device member

Return Value:

TRUE / FALSE. This decides whether to continue or not

--*/

{

SP_DEVICE_INTERFACE_DATA interfaceData;

PSP_DEVICE_INTERFACE_DETAIL_DATA interfaceDetailData = NULL;

STORAGE_PROPERTY_QUERY query;

PSTORAGE_ADAPTER_DESCRIPTOR adpDesc;

PSTORAGE_DEVICE_DESCRIPTOR devDesc;

SCSI_PASS_THROUGH_WITH_BUFFERS sptwb;

PMOUNTDEV_NAME mountName;

PSCSI_ADDRESS scsiAddress;

HANDLE hDevice;

BOOL status;

PUCHAR p;

UCHAR outBuf[BUF_LEN];

ULONG returnedLength;

ULONG length = 0,

returned = 0;

DWORD interfaceDetailDataSize,

reqSize,

errorCode,

PMOUNTDEV_UNIQUE_ID mountId;

STORAGE_DEVICE_NUMBER number;

SP_DEVINFO_DATA deid;

DWORD dwRegType;

char szPdoName[MAX_FRIENDLY];

char buffer[2048];

//PDRIVE_LAYOUT_INFORMATION_EX DriveLayout = (PDRIVE_LAYOUT_INFORMATION_EX) buffer;

PDRIVE_LAYOUT_INFORMATION DriveLayout = (PDRIVE_LAYOUT_INFORMATION) buffer;

PARTITION_INFORMATION PartInfo;

PARTITION_INFORMATION_EX PartInfoEx;

interfaceData.cbSize = sizeof (SP_INTERFACE_DEVICE_DATA);

status = SetupDiEnumDeviceInterfaces (

IntDevInfo, // Interface Device Info handle

0, // Device Info data

(LPGUID)&VolumeClassGuid,

Index, // Member

&interfaceData // Device Interface Data

);

if ( status == FALSE ) {

errorCode = GetLastError();

if ( errorCode == ERROR_NO_MORE_ITEMS ) {

DebugPrint( 2, "No more interfaces\n" );

}

else {

DebugPrint( 1, "SetupDiEnumDeviceInterfaces failed with error: %d\n", errorCode );

}

return FALSE;

}

// Find out required buffer size, so pass NULL

status = SetupDiGetDeviceInterfaceDetail (

IntDevInfo, // Interface Device info handle

&interfaceData, // Interface data for the event class

NULL, // Checking for buffer size

0, // Checking for buffer size

&reqSize, // Buffer size required to get the detail data

NULL // Checking for buffer size

);

// This call returns ERROR_INSUFFICIENT_BUFFER with reqSize

// set to the required buffer size. Ignore the above error and

// pass a bigger buffer to get the detail data

if ( status == FALSE ) {

errorCode = GetLastError();

if ( errorCode != ERROR_INSUFFICIENT_BUFFER ) {

DebugPrint( 1, "SetupDiGetDeviceInterfaceDetail failed with error: %d\n", errorCode );

return FALSE;

}

// Allocate memory to get the interface detail data

// This contains the devicepath we need to open the device

interfaceDetailDataSize = reqSize;

interfaceDetailData = malloc (interfaceDetailDataSize);

if ( interfaceDetailData == NULL ) {

DebugPrint( 1, "Unable to allocate memory to get the interface detail data.\n" );

return FALSE;

}

interfaceDetailData->cbSize = sizeof (SP_INTERFACE_DEVICE_DETAIL_DATA);

status = SetupDiGetDeviceInterfaceDetail (

IntDevInfo, // Interface Device info handle

&interfaceData, // Interface data for the event class

interfaceDetailData, // Interface detail data

interfaceDetailDataSize, // Interface detail data size

&reqSize, // Buffer size required to get the detail data

NULL); // Interface device info

if ( status == FALSE ) {

DebugPrint( 1, "Error in SetupDiGetDeviceInterfaceDetail failed with error: %d\n", GetLastError() );

return FALSE;

}

//printf("Interface: %s\n", interfaceDetailData->DevicePath);

memset(szPdoName, 0, MAX_FRIENDLY);

deid.cbSize = sizeof(SP_DEVINFO_DATA);

SetupDiEnumDeviceInfo(IntDevInfo, Index, &deid);

SetupDiGetDeviceRegistryProperty(IntDevInfo, &deid,

SPDRP_PHYSICAL_DEVICE_OBJECT_NAME,

&dwRegType,

(BYTE*) szPdoName,

MAX_FRIENDLY,

NULL);

//printf(" PdoName : %s\n", szPdoName);

// Now we have the device path. Open the device interface

// to send Pass Through command

hDevice = CreateFile(

interfaceDetailData->DevicePath, // device interface name

GENERIC_READ | GENERIC_WRITE, // dwDesiredAccess

FILE_SHARE_READ | FILE_SHARE_WRITE, // dwShareMode

NULL, // lpSecurityAttributes

OPEN_EXISTING, // dwCreationDistribution

0, // dwFlagsAndAttributes

NULL // hTemplateFile

);

if (hDevice == INVALID_HANDLE_VALUE) {

DebugPrint( 1, "CreateFile failed with error: %d\n", GetLastError() );

return TRUE;

}

free (interfaceDetailData);

if (hDevice == INVALID_HANDLE_VALUE) {

DebugPrint( 1, "CreateFile failed with error: %d\n", GetLastError() );

return TRUE;

}

IsFixedDisk = FALSE;

status = DeviceIoControl(

hDevice,

IOCTL_MOUNTDEV_QUERY_DEVICE_NAME,

&outBuf,

BUF_LEN,

&outBuf,

BUF_LEN,

&returnedLength,

NULL

);

if ( !status ) {

DebugPrint( 1, "\nIOCTL_MOUNTDEV_QUERY_DEVICE_NAME failed with error code: %d.\n\n", GetLastError() );

}

else {

mountName = (PMOUNTDEV_NAME)&outBuf;

#if 0

if (!found) {

if (wcsstr(mountName->Name, L"Volume\0")) {

wcsncpy(FoundDevice, mountName->Name, mountName->NameLength);

//swprintf(FoundDevice, L"%s", mountName->Name);

found = TRUE;

printf("\noh yeah we found the device = %ws\n", FoundDevice);

}

#endif

}

// Get Drive letter from mount name

if (GetStorageDeviceNumber(hDevice, &number)) {

if (number.PartitionNumber != -1) {

GetDriveLetter(mountName);

printf("Disk #%d, Partition #%d", number.DeviceNumber, number.PartitionNumber);

if (GetPartitionInfoEx(hDevice, &PartInfoEx)) {

printf("\tOffset 0x%I64x\n", PartInfoEx.StartingOffset);

} else {

printf("[not available for this device]\n");

}

// Close handle the driver

if ( !CloseHandle(hDevice) ) {

DebugPrint( 2, "Failed to close device.\n");

}

return TRUE;

}

void GetDriveLetter(PMOUNTDEV_NAME mountName)

{

HANDLE hDevice;

BOOL status;

ULONG returnedLength,

nameLength,

mountPointsSize;

UCHAR outBuf[BUF_LEN];

PMOUNTMGR_MOUNT_POINTS mountMgrQueryPoints;

PMOUNTMGR_MOUNT_POINT pMountPoint;

USHORT i;

WCHAR volumeGuid[255];

BOOL showedDevice;

PWCHAR pName;

hDevice = CreateFile(

MOUNTMGR_NAME, // device interface name

GENERIC_READ, // dwDesiredAccess

FILE_SHARE_READ, // dwShareMode

NULL, // lpSecurityAttributes

OPEN_EXISTING, // dwCreationDistribution

0, // dwFlagsAndAttributes

NULL // hTemplateFile

);

if (hDevice == INVALID_HANDLE_VALUE) {

DebugPrint( 1, "CreateFile failed with error: %d\n", GetLastError() );

return;

}

nameLength = mountName->NameLength;

mountPointsSize = sizeof(MOUNTMGR_MOUNT_POINT) + nameLength;

pMountPoint = malloc(mountPointsSize);

ZeroMemory(pMountPoint, mountPointsSize );

pMountPoint->DeviceNameOffset = (USHORT) sizeof(MOUNTMGR_MOUNT_POINT);

pMountPoint->DeviceNameLength = (USHORT) nameLength;

memcpy( pMountPoint + 1, mountName->Name, nameLength );

ZeroMemory(outBuf, BUF_LEN );

// Get the triples (symbolic links, mount name & unique ID) from Mount Manager

status = DeviceIoControl(

hDevice,

IOCTL_MOUNTMGR_QUERY_POINTS,

pMountPoint,

mountPointsSize,

&outBuf,

BUF_LEN,

&returnedLength,

NULL

);

if ( !status ) {

DebugPrint( 1, "\nIOCTL_MOUNTMGR_QUERY_POINTS failed with error code: %d.\n\n", GetLastError() );

}

mountMgrQueryPoints = (PMOUNTMGR_MOUNT_POINTS) outBuf;

showedDevice = TRUE;

for (i = 0; i < mountMgrQueryPoints->NumberOfMountPoints - 1; i++ ) {

pMountPoint = &mountMgrQueryPoints->MountPoints[i];

if (!showedDevice) {

if (pMountPoint->DeviceNameLength) {

DebugPrint( 1, " Device Name: ");

PrintName( (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->DeviceNameOffset), pMountPoint->DeviceNameLength/2);

printf("\n");

}

if (pMountPoint->UniqueIdLength) {

DebugPrint( 1, " Unique Id: ");

PrintName( (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->UniqueIdOffset), pMountPoint->UniqueIdLength/2);

printf("\n");

}

showedDevice = TRUE;

}

if (pMountPoint->SymbolicLinkNameLength) {

//pName = (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->SymbolicLinkNameOffset);

//if (wcsstr(pName, L"DosDevices")) {

// printf("got DosDevices...\n");

// //PrintName( pName, (pMountPoint->SymbolicLinkNameLength/2));

// PrintName( (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->SymbolicLinkNameOffset), (pMountPoint->SymbolicLinkNameLength/2));

// printf("\n");

//}

pName = (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->SymbolicLinkNameOffset);

if (wcsstr(pName, L"Volume")) {

pName = (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->SymbolicLinkNameOffset);

pName += 11;

PrintName( pName, (pMountPoint->SymbolicLinkNameLength/2)-12);

printf("\t");

}

//PrintName( (PWCHAR)((PCHAR)mountMgrQueryPoints + pMountPoint->SymbolicLinkNameOffset), (pMountPoint->SymbolicLinkNameLength/2));

}

// Close handle the driver

if ( !CloseHandle(hDevice) ) {

DebugPrint( 1, "Failed to close device.\n");

}

free(pMountPoint);

return;

}

/**************************************************mounts.c*************************************************/

/*************************************************MakeFile**************************************************/

# DO NOT EDIT THIS FILE!!! Edit .\sources. if you want to add a new source

# file to this component. This file merely indirects to the real make file

# that is shared by all the driver components of the Windows NT DDK

!INCLUDE $(NTMAKEENV)\makefile.def

/*************************************************MakeFile**************************************************/

/*************************************************Sources***************************************************/

TARGETNAME=enumvol

TARGETTYPE=PROGRAM

UMTYPE=console

UMBASE=0x1000000

USE_LIBCMT=1

TARGETPATH=obj

INCLUDES=$(DDK_INC_PATH); \

$(BASEDIR)\inc; \

$(BASEDIR)\inc\ddk;

TARGETLIBS= $(DDK_LIB_PATH)\setupapi.lib

SOURCES=mounts.c

/*************************************************Sources**********************************************

Comments

Anonymous
January 07, 2014
There's a memory corruption error in the GetDrive function. fee is called on a pointer that didn't come from the heap. Near the top: pMountPoint = malloc(mountPointsSize); Later, the loop for (i = 0; i < mountMgrQueryPoints->NumberOfMountPoints - 1; i++ ) contains: pMountPoint = &mountMgrQueryPoints->MountPoints[i]; thereby bashing the original pMountPoint then right before the return, fee is called: free(pMountPoint); but that's no longer the pMountPoint we got from malloc. I simply changed the pMountPoint assignment within the loop to be: PMOUNTMGR_MOUNT_POINT pMountPoint = &mountMgrQueryPoints->MountPoints[i]; so it's a locally scoped pMountPoint and doesn't bash the one that came from malloc.

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Mapping VolumeID to Disk partition Using the DeviceIOControl API

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