PRB: DeviceIoControl Int 13h Does Not Support Hard Disks

This article was previously published under Q137176
This article has been archived. It is offered "as is" and will no longer be updated.
Symptoms
Win32 applications running under Windows 95 use CreateFile to openVWIN32 and then use DeviceIoControl with the VWIN32_DIOC_DOS_INT13 flag toperform low-level BIOS disk functions. The functions work on floppydisks but always fail on hard disks.
Cause
Windows 95, like previous versions of Windows, does not support callingBIOS disk functions to gain access to hard disks from Win16 and Win32applications. The reason is that BIOSXLAT.VXD does not translate BIOSrequests to hard disks from protected-mode into V86 mode, and this causesthe ROM BIOS to be called with an invalid address.
Resolution
To work around this problem, Win32 applications must thunk to a Win16 DLLand have that DLL call the DOS Protected Mode Interface (DPMI) SimulateReal Mode Interrupt function to call Int 13h BIOS disk functions on harddisks. When you use DPMI to call Int 13h BIOS disk functions, you bypassBIOSXLAT.VXD and call the real-mode BIOS. Note that you cannot call DPMIfrom 32-bit code.
Status
This behavior is by design.
More information
The following example code shows how a Win32 application running underWindows 95 can read the first physical sector of a hard disk, whichcontains the disk's partition tables. This code requires a flat thunk, soparts of it must be placed in a Win32 DLL and other parts must be placed ina Win16 DLL. The relevant code for each DLL is labeled.

Execution starts from a Win32 application calling the Win32 DLL andproceeds as follows. The Win32 DLL function, CallReadPhysicalSector1, callsthe Win16 DLL's ReadPhysicalSector1 function by way of a thunk. ThenReadPhysicalSector1, which is exported by the 16-bit DLL, calls DPMI tocall the BIOS Read Track function to read the first sector of the specifiedhard disk. After ReadPhysicalSector1 returns, the contents of the firstsector of the hard disk, including the hard disk's partition table andbootstrap program, will be in the buffer pointed to by lpBuff.

Code Sample

//--------------------------------------------------------------------// Code in the 32-bit DLL// Prototype for function in 16-bit DLL.BOOL FAR PASCAL ReadPhysicalSector1 (BYTE   bDrive,                                     LPBYTE lpBuffer,                                     DWORD  cbBuffSize);/*-------------------------------------------------------------------- CallReadPhysicalSector1() Reads the first sector of the first hard disk. Return Value    Returns TRUE if the first sector was read, and FALSE if it    wasn't.--------------------------------------------------------------------*/ __declspec(dllexport) BOOL WINAPI CallReadPhysicalSector1(){    char lpBuff[512];    BOOL fResult;    // Read the first sector of the first hard disk.    fResult = ReadPhysicalSector1 (0x80, lpBuff, 512);    if (fResult)       {        // lpBuff contains the sector data.  Use it here       }    return fResult;}//--------------------------------------------------------------------// Thunk Scriptenablemapdirect3216 = true;typedef unsigned long   DWORD;typedef unsigned char   BYTE, * LPBYTE;typedef bool            BOOL;BOOL ReadPhysicalSector1 (BYTE   bDrive,                          LPBYTE lpBuffer,                          DWORD  cbBuffSize){   lpBuffer = inout;}//--------------------------------------------------------------------// Code in the 16-bit DLL// Converts two BYTEs into a WORD.  This is useful for working with// a RMCS, but was not provided in WINDOWS.H.//#define MAKEWORD(low, high) \            ((WORD)((((WORD)(high)) << 8) | ((BYTE)(low))))#define SECTOR_SIZE 512       // Size, in bytes, of a disk sector#define CARRY_FLAG  0x0001typedef BYTE FAR *LPBYTE;typedef struct tagRMCS{   DWORD edi, esi, ebp, RESERVED, ebx, edx, ecx, eax;   WORD  wFlags, es, ds, fs, gs, ip, cs, sp, ss;} RMCS, FAR* LPRMCS;BOOL FAR PASCAL SimulateRM_Int (BYTE bIntNum, LPRMCS lpCallStruct);void FAR PASCAL BuildRMCS (LPRMCS lpCallStruct);BOOL FAR PASCAL __export ReadPhysicalSector1 (BYTE   bDrive,                                              LPBYTE lpBuffer,                                              DWORD  cbBuffSize);/*--------------------------------------------------------------------  ReadPhysicalSector1()  Calls DPMI to call the BIOS Int 13h Read Track function to read the  first physical sector of a physical drive. This function is used to  read partition tables, for example.  Parameters     bDrive        The Int 13h device unit,           0x00 for floppy drive 0           0x00 for floppy drive 1           0x80 for physical hard disk 0           0x81 for physical hard disk 1           etc.     lpBuffer        Pointer to a buffer that receives the sector data.  The buffer        must be at least SECTOR_SIZE bytes long.     cbBuffSize        Actual size of lpBuffer.  Return Value     Returns TRUE if the first sector was read into the buffer pointed     to by lpBuffer, or FALSE otherwise.  Assumptions     Assumes that sectors are at least SECTOR_SIZE bytes long.--------------------------------------------------------------------*/ BOOL FAR PASCAL __export ReadPhysicalSector1 (BYTE   bDrive,                                              LPBYTE lpBuffer,                                              DWORD  cbBuffSize){   BOOL   fResult;   RMCS   callStruct;   DWORD  gdaBuffer;     // Return value of GlobalDosAlloc().   LPBYTE RMlpBuffer;    // Real-mode buffer pointer   LPBYTE PMlpBuffer;    // Protected-mode buffer pointer   /*     Validate params:        bDrive should be int 13h device unit -- let the BIOS validate           this parameter -- user could have a special controller with           its own BIOS.        lpBuffer must not be NULL        cbBuffSize must be large enough to hold a single sector   */    if (lpBuffer == NULL || cbBuffSize < SECTOR_SIZE)      return FALSE;   /*     Allocate the buffer that the Int 13h function will put the sector     data into. As this function uses DPMI to call the real-mode BIOS, it     must allocate the buffer below 1 MB, and must use a real-mode     paragraph-segment address.     After the memory has been allocated, create real-mode and     protected-mode pointers to the buffer. The real-mode pointer     will be used by the BIOS, and the protected-mode pointer will be     used by this function because it resides in a Windows 16-bit DLL,     which runs in protected mode.   */    gdaBuffer = GlobalDosAlloc (cbBuffSize);   if (!gdaBuffer)      return FALSE;   RMlpBuffer = (LPBYTE)MAKELONG(0, HIWORD(gdaBuffer));   PMlpBuffer = (LPBYTE)MAKELONG(0, LOWORD(gdaBuffer));   /*     Initialize the real-mode call structure and set all values needed     to read the first sector of the specified physical drive.   */    BuildRMCS (&callStruct);   callStruct.eax = 0x0201;                // BIOS read, 1 sector   callStruct.ecx = 0x0001;                // Sector 1, Cylinder 0   callStruct.edx = MAKEWORD(bDrive, 0);   // Head 0, Drive #   callStruct.ebx = LOWORD(RMlpBuffer);    // Offset of sector buffer   callStruct.es  = HIWORD(RMlpBuffer);    // Segment of sector buffer   /*      Call Int 13h BIOS Read Track and check both the DPMI call      itself and the BIOS Read Track function result for success.  If      successful, copy the sector data retrieved by the BIOS into the      caller's buffer.   */    if (fResult = SimulateRM_Int (0x13, &callStruct))      if (!(callStruct.wFlags & CARRY_FLAG))         {         _fmemcpy (lpBuffer, PMlpBuffer, (size_t)cbBuffSize);         fResult = TRUE;         }      else         fResult = FALSE;   // Free the sector data buffer this function allocated   GlobalDosFree (LOWORD(gdaBuffer));   return fResult;}/*--------------------------------------------------------------------  SimulateRM_Int()  Allows protected mode software to execute real mode interrupts such  as calls to DOS TSRs, DOS device drivers, etc.  This function implements the "Simulate Real Mode Interrupt" function  of the DPMI specification v0.9.  Parameters     bIntNum        Number of the interrupt to simulate     lpCallStruct        Call structure that contains params (register values) for        bIntNum.  Return Value     SimulateRM_Int returns TRUE if it succeeded or FALSE if it     failed.  Comments     lpCallStruct is a protected-mode selector:offset address, not a     real-mode segment:offset address.--------------------------------------------------------------------*/ BOOL FAR PASCAL SimulateRM_Int (BYTE bIntNum, LPRMCS lpCallStruct)   {   BOOL fRetVal = FALSE;      // Assume failure   _asm {         push di         mov  ax, 0300h         ; DPMI Simulate Real Mode Int         mov  bl, bIntNum       ; Number of the interrupt to simulate         mov  bh, 01h           ; Bit 0 = 1; all other bits must be 0         xor  cx, cx            ; No words to copy         les  di, lpCallStruct         int  31h                   ; Call DPMI         jc   END1                  ; CF set if error occurred         mov  fRetVal, TRUE      END1:         pop di        }   return (fRetVal);   }/*--------------------------------------------------------------------  BuildRMCS()  Initializes a real mode call structure to contain zeros in all its  members.  Parameters:     lpCallStruct        Points to a real mode call structure  Comments:     lpCallStruct is a protected-mode selector:offset address, not a     real-mode segment:offset address.--------------------------------------------------------------------*/ void FAR PASCAL BuildRMCS (LPRMCS lpCallStruct)   {   _fmemset (lpCallStruct, 0, sizeof (RMCS));   }				
References
Information on using DPMI may be found in the DOS Protected ModeInterface (DPMI) Specification Version 0.9.

Flat thunks are documented in "The Microsoft Programmer's Guide ToWindows 95" topic in the Win32 Software Development Kit onlinedocumentation.
Windows sector table physical
Properties

Article ID: 137176 - Last Review: 10/26/2013 03:05:00 - Revision: 4.0

  • Microsoft Win32 Application Programming Interface
  • kbnosurvey kbarchive kbapi kbkernbase KB137176
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