DOCUMENT:Q104790  06-NOV-1999  [win16sdk]
TITLE   :Using Int 21h Get/Set Media ID in the Windows Environment
PRODUCT :Microsoft Windows Software Development Kit
PROD/VER:WINDOWS:3.0,3.1
OPER/SYS:
KEYWORDS:_IK kb16bitonly

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The information in this article applies to:

 - Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 
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SUMMARY
=======

The Interrupt 21h Generic IOCTL for Block Devices functions Get Media ID and Set
Media ID cannot be used directly from a protected mode application in the
Windows operating environment. However, these functions can be used in
conjunction with the DPMI function Simulate Real Mode Interrupt.

MORE INFORMATION
================

The following Interrupt 21h AX=440Dh Generic IOCTL for Block Devices functions
are automatically translated from protected mode by the DOSMGR VxD:

   40h - Set Device Parameters
   41h - Write Track on Logical Drive
   42h - Format Track on Logical Drive
   60h - Get Device Parameters
   61h - Read Track on Logical Drive
   62h - Verify Track on Logical Drive
   68h - Sense Media Type

The following are not automatically translated by the DOSMGR VxD:

   46h - Set Media ID
   66h - Get Media ID

To use the Get Media ID or Set Media ID functions from a protected mode
application in the Windows operating environment, the DPMI function Simulate
Real Mode Interrupt must be used to manually translate the buffer pointer from
protected mode to real mode.

The sample code below illustrates how the Get Media ID function can be manually
translated by:

1. Allocating a real mode addressable buffer using GlobalDosAlloc().

2. Initializing a DPMI real mode register structure with a real mode pointer to
   the buffer.

3. Issuing the interrupt in real mode using the DPMI function Simulate Real Mode
   Interrupt.

4. If successful, the content of the real mode addressable buffer is copied to
   the protected mode destination buffer.

5. The real mode addressable buffer is freed.

To translate the Set Media ID function, the contents of the protected mode source
buffer would be copied to the real mode addressable buffer before issuing the
interrupt in real mode.

Sample Code
-----------

   // This is a standard MS-DOS structure.
   typedef struct tagMEDIAID
   {
       WORD  wInfoLevel;
       DWORD dwSerialNum;     // Serial number
       char  VolLabel[11];    // ASCII volume label
       char  FileSysType[8];  // File system type
   } MEDIAID, far *LPMEDIAID;

   // This is a standard DPMI structure.
   typedef struct tagREALMODEREG {
       DWORD rmEDI, rmESI, rmEBP, Reserved, rmEBX, rmEDX, rmECX, rmEAX;
       WORD  rmCPUFlags, rmES, rmDS, rmFS, rmGS, rmIP, rmCS, rmSP, rmSS;
   } REALMODEREG, FAR *LPREALMODEREG;

   //********************************************************************
   // RealInt()
   // 
   // Simulate an interrupt in real mode using DPMI function 0300h
   // When the interrupt is simulated in real mode, the registers will
   // contain the values in lpRealModeReg. When the interrupt returns,
   // lpRealModeReg will contain the values from real mode.
   // 
   //********************************************************************

   BOOL RealInt (BYTE intnum, LPREALMODEREG lpRealModeReg)
   {
      BOOL bRetVal = TRUE;

      _asm
      {
          mov  ax, 0300h  // Simulate real mode interrupt
          mov  bl, intnum // Interrupt number to simulate
          mov  bh, 0      // Flags
          mov  cx, 0      // Number of words to copy on stack
          les  di, lpRealModeReg
          int  31h
          jnc  Done
          mov  bRetVal, FALSE
      Done:
      }
      return bRetVal;
   }

   //********************************************************************
   // GetMediaID()
   // 
   // Get Media ID by simulating an Interrupt 21h, AX=440Dh, CX=0866h in
   // real mode. Set up RealModeReg to contain a real mode pointer to a
   // MediaID structure.
   //********************************************************************

   BOOL GetMediaID (WORD      Drive,
                    LPMEDIAID lpMediaID)
   {
      REALMODEREG RealModeReg;
      DWORD       dwGlobalDosBuffer;
      LPMEDIAID   lpRMMediaID;
      BOOL        bRetVal;

      // (1) Get a real mode addressable buffer for the MediaID structure.
      // 
      dwGlobalDosBuffer = GlobalDosAlloc(sizeof(MEDIAID));
      if (dwGlobalDosBuffer == NULL)
      {
          return FALSE;
      }

      // (2) Initialize the real mode register structure.
      // 
      memset(&RealModeReg, 0, sizeof(RealModeReg));
      (WORD)RealModeReg.rmEAX = 0x440D;  // IOCTL for Block Device
      (WORD)RealModeReg.rmEBX = Drive;   // 0 = default, 1 = A, 2 = B
      (WORD)RealModeReg.rmECX = 0x0866;  // Get Media ID
      // Set the real mode DS:DX to a real mode pointer to the buffer.
      // The offset in DX is zero from the memset().
      RealModeReg.rmDS  = HIWORD(dwGlobalDosBuffer);

      // (3) Simulate the real mode interrupt.
      // 
      if (RealInt(0x21, &RealModeReg) &&         // Int simulation ok?
          (RealModeReg.rmCPUFlags & 0x0001)==0)  // Carry clear?
      {
          // (4) Copy the content of the real mode addressable buffer
          //     to the protected mode destination buffer.
          // 
          lpRMMediaID = (LPMEDIAID) MAKELP(LOWORD(dwGlobalDosBuffer), 0);
          *lpMediaID = *lpRMMediaID;  // Structure copy
          bRetVal = TRUE;
      }
      else
      {
          bRetVal = FALSE;
      }

      // (5) Free the real mode addressable buffer.
      // 
      GlobalDosFree(LOWORD(dwGlobalDosBuffer));

      return bRetVal;
   }

For more information on the DOS Protected Mode Interface (DPMI), see the DPMI
version 0.9 specification, which is available on the Microsoft Developer Network
CD Disk Four.

Additional query words: serial number volume label

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Keywords          : _IK kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : WINDOWS:3.0,3.1
Issue type        : kbhowto

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