windows-server-2003/multimedia/media/winmm/mmio.c

/* Copyright (c) 1991-1999 Microsoft Corporation */
/*-------------------------------------------------------------------*\
 *
 * mmio.c
 *
 * Basic MMIO functions.
 *
\*-------------------------------------------------------------------*/

/*--------------------------------------------------------------------*/
/* Revision history:
 * LaurieGr: Jan 92 Ported from win16.  Source tree fork, not common code.
 * StephenE: Apr 92 Enabled UNICODE.
 */
/*--------------------------------------------------------------------*/


/*--------------------------------------------------------------------*/
/* Implementation notes:
 *
 * An HMMIO is in fact a PMMIO i.e. a pointer to a MMIOINFO.
 * This causes the code to be littered with casts.
 * Whoever exported MMIOINFO should learn about encapsulation and
 * all that stuff.  sigh.
 *
 * The "current disk offset" is the disk offset (i.e. the location
 * in the disk file) that the next MMIOM_READ or MMIOM_WRITE will
 * read from or write to.  The I/O procedure maintains the
 * <lDiskOffset> field of the file's MMIO structure so that
 * <lDiskOffset> is equal to the current disk offset.
 *
 * The "current buffered offset" is the disk offset that the next
 * mmioRead() or mmioWrite() call would read from or write to.
 * The current buffered offset is defined as
 *
 *  <lBufOffset> + (<pchNext> - <pchBuffer>)
 *
 * since <lBufOffset> is the disk offset of the start of the buffer
 * and <pchNext> corresponds to the current buffered offset.
 *
 * If the file is unbuffered, then <pchBuffer>, <pchNext>,
 * <pchEndRead> and <pchEndWrite> will always be NULL, and
 * <lBufOffset> will always be considered the "current buffered
 * offset", i.e. mmioRead() and mmioWrite() will read/write
 * at this offset.
 *
 *
 * Except right at the beginning of mmioOpen(), the MMIO_ALLOCBUF
 * flag is set if and only if the pchBuffer field points to a block
 * of global memory that MMIO has allocated.
 */
/*--------------------------------------------------------------------*/

#include "winmmi.h"
#include "mmioi.h"


/*--------------------------------------------------------------------*\
 * Local function prototypes
\*--------------------------------------------------------------------*/
static void NEAR PASCAL SetIOProc( LPCWSTR szFileName, LPMMIOINFO lpmmio);
static LPMMIOPROC NEAR PASCAL RemoveIOProc(FOURCC fccIOProc, HANDLE htask);
static LONG NEAR PASCAL mmioDiskIO(PMMIO pmmio, UINT uMsg, LPSTR pch, LONG cch);
static UINT NEAR PASCAL mmioExpandMemFile(PMMIO pmmio, LONG lExpand);
static LPMMIOPROC mmioInternalInstallIOProc( FOURCC fccIOProc,
                                             LPMMIOPROC pIOProc,
                                             DWORD dwFlags);

/*--------------------------------------------------------------------*/
/* The I/O procedure map is a linked list of IOProcMapEntry structures.
 * The head of the list, <gIOProcMapHead> is a pointer node to the last
 * entry registered.  The first few elements of the list are the predefined
 * global IO procedures below -- these all have <hTask> equal to NULL so
 * that no task can unregister them.
 *
 */

typedef struct IOProcMapEntryTag
{
        FOURCC          fccIOProc;      // ID of installed I/O procedure
        LPMMIOPROC      pIOProc;        // I/O procedure address
        HANDLE          hTask;          // task that called mmioRegisterIOProc()
        struct IOProcMapEntryTag *pNext;  // pointer to next IOProc entry
} IOProcMapEntry, *pIOProcMapEntry;

// MMIOPROC is defined in the public MMSYSTEM.H
// typedef LONG (APIENTRY MMIOPROC)(LPSTR lpmmioinfo, UINT uMsg, LONG lParam1, LONG lParam2);

MMIOPROC mmioDOSIOProc, mmioMEMIOProc; // standard I/O procedures

static IOProcMapEntry gIOProcMaps[] = {
    { FOURCC_DOS, mmioDOSIOProc, NULL,  &gIOProcMaps[1] },
    { FOURCC_MEM, mmioMEMIOProc, NULL,  NULL }
};

//
// Global head of list
//

static pIOProcMapEntry gIOProcMapHead = gIOProcMaps;

#ifdef DUMPIOPROCLIST
/* debug dump of ioproclist */
static void DumpIOProcList(void)
{  pIOProcMapEntry pph;

   dprintf(("gIOProcMapHead= %8x\n",gIOProcMapHead ));
   for (pph = gIOProcMapHead;pph ;pph=pph->pNext)
   {  dprintf(( "fourcc=%c%c%c%c pioproc=%8x hTask=%8x\n"
             , pph->fccIOProc/16777216
             , (pph->fccIOProc/65536)%256
             , (pph->fccIOProc/256)%256
             , (pph->fccIOProc)%256
             , pph->pIOProc
             , pph->hTask
             ));
   }
} /* DumpIOProcList */
#endif


/* Call the IOProc in the info structure and return the result.
   Take due account of whether it is a 16 or 32 bit IOProc.
*/
static LRESULT IOProc(LPMMIOINFO lpmmioinfo, UINT uMsg, LPARAM lParam1, LPARAM lParam2)
{
    /*  just pass the call on */
    return ((LPMMIOPROC)(lpmmioinfo->pIOProc)) ((LPSTR)lpmmioinfo, uMsg, lParam1, lParam2);
} /* IOProc */

/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@func   LPMMIOPROC | FindIOProc | This function locates the IOProcMapEntry
    for a previously installed IO procedure .
*/
/*--------------------------------------------------------------------*/
static pIOProcMapEntry
                  FindIOProc(FOURCC fccIOProc, HANDLE htask)
{
    IOProcMapEntry *pEnt;       // an entry in linked list

    /* walk through the linked list, first looking for an entry with
     * identifier <fccIOProc> that was added by the current task, then
     * looking for global entries.
     */

    for (pEnt = gIOProcMapHead; pEnt; pEnt = pEnt->pNext)
        if ((pEnt->fccIOProc == fccIOProc) && (pEnt->hTask == htask))
            return pEnt;

    for (pEnt = gIOProcMapHead; pEnt; pEnt = pEnt->pNext)
        if ( (pEnt->fccIOProc == fccIOProc)
                                           // ?? && (pEnt->hTask ==NULL)  ??
           )
            return pEnt;

    return NULL;
}

/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@func   LPMMIOPROC | RemoveIOProc | This function removes previously installed
    IO procedure.
*/
/*--------------------------------------------------------------------*/
static LPMMIOPROC PASCAL NEAR
                  RemoveIOProc(FOURCC fccIOProc, HANDLE htask)
{
    IOProcMapEntry *pEnt;       // an entry in linked list
    IOProcMapEntry *pEntPrev;   // the entry before <pEnt>

    /* walk through the linked list, looking for an entry with
     * identifier <fccIOProc> that was added by the current task
     */
    for ( pEntPrev = NULL, pEnt = gIOProcMapHead
        ; pEnt
        ; pEntPrev = pEnt, pEnt = pEnt->pNext
        )
        if ((pEnt->fccIOProc == fccIOProc) && (pEnt->hTask == htask)) {
            LPMMIOPROC  pIOProc;

            pIOProc = pEnt->pIOProc;
            if (pEntPrev)
                pEntPrev->pNext = pEnt->pNext;
            else
                gIOProcMapHead = pEnt->pNext;
            FreeHandle((HMMIO) pEnt);
            return pIOProc;
        }
    return NULL;
}

/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@func   void | SetIOProc | This function sets the physical IO procedure
    based on either the file name or the parameters within the
    <p lpmmioinfo> structure passed.

@parm   LPCWSTR | szFilename | Specifies a pointer to a string
containing the filename of the file to open. If no I/O procedure is

@parm   LPMMIOINFO | lpmmioinfo | Specifies a pointer to an
    <t MMIOINFO> structure containing extra parameters used by
    <f SetIOProc> in determining the IO procedure to use.  The
    <e MMIOINFO.pIOProc> element is set to the procedure found.

@rdesc  Nothing.
*/
/*--------------------------------------------------------------------*/
static void NEAR PASCAL
            SetIOProc( LPCWSTR szFileName, LPMMIOINFO lpmmio)
{
    IOProcMapEntry *pEnt;       // the entry in linked list

    /* If the IOProc is not given, see if the file name implies that
     * <szFileName> is either a RIFF compound file or some kind of
     * other registered storage system -- look for the last CFSEPCHAR in
     * the name, e.g. '+' in "foo.bnd+bar.hlp+blorg.dib", and figure
     * that the IOProc ID is the extension of the compound file name,
     * e.g. the extension of "foo.bnd+bar.hlp", i.e. 'HLP '.
     *
     * Alternatively, if <szFileName> is NULL, then assume that
     * <lpmmio->adwInfo[0]> is a DOS file handle.
    */
    if (lpmmio->pIOProc == NULL)
    {
        if (lpmmio->fccIOProc == 0)
        {
            if (szFileName != NULL)
            {
                LPWSTR   pch;

                /* see if <szFileName> contains CFSEPCHAR */
                if ((pch = wcsrchr(szFileName, CFSEPCHAR)) != 0)
                {
                    /* find the extension that precedes CFSEPCHAR,
                     * e.g. "hlp" in "foo.bnd+bar.hlp+blorg.dib"
                    */
                    while (  (pch > szFileName)
                          && (*pch != '.')
                          && (*pch != ':')
                          && (*pch != '\\')
                          )
                        pch--;
                    if (*pch == '.')
                    {
                        WCHAR    aszFour[sizeof(FOURCC)+1];
                        int i;

                        for (i = 0, pch++; i < sizeof(FOURCC); i++)
                            if (*pch == CFSEPCHAR)
                                aszFour[i] = (WCHAR)0;
                            else
                                aszFour[i] = *pch++;
                        aszFour[sizeof(FOURCC)] = (WCHAR)0;
                        lpmmio->fccIOProc
                                 = mmioStringToFOURCCW(aszFour, MMIO_TOUPPER);
                    }
                }
            }
            /* if the caller didn't specify an IOProc, and the code above
             * didn't determine an IOProc ID, then the default is the DOS
             * IOProc.
            */
            if (lpmmio->fccIOProc == 0)
                lpmmio->fccIOProc = FOURCC_DOS;
        }

        /* unless an IOProc address is specified explicitly, look up the
         * IOProc in the global IOProc ID-to-address table -- the default
         * is 'DOS' since we'll assume that custom storage system I/O
         * procedures would have been installed
        */
        pEnt = FindIOProc( lpmmio->fccIOProc
                         ,   lpmmio->htask
                           ? lpmmio->htask
                           : GetCurrentTask()
                         );
        if (pEnt && pEnt->pIOProc) {
            lpmmio->pIOProc = pEnt -> pIOProc;
        }
        else {
            lpmmio->pIOProc = mmioDOSIOProc;
            lpmmio->dwReserved1 = 0;
        }
    }
}


/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@func   void | mmioCleanupIOProcs | removes from the linked list entries
    installed with the given task handle

@parm   HANDLE | hTask | Specifies the task to clean up for

@rdesc  Nothing.

@comm  This will only be called to clean up a WOW task.
*/
/*--------------------------------------------------------------------*/
void mmioCleanupIOProcs(HANDLE hTask)
{
     IOProcMapEntry *pEnt;
     IOProcMapEntry *pEntPrev;

     for (pEntPrev = NULL, pEnt = gIOProcMapHead; pEnt;) {

        if (pEnt->hTask == hTask) {
            dprintf1(("MMIOPROC handle (%04X) not closed.", pEnt));
            if (pEntPrev) {
                pEntPrev->pNext = pEnt->pNext;
                FreeHandle((HMMIO)pEnt);
                pEnt = pEntPrev->pNext;
            } else {
                gIOProcMapHead = pEnt->pNext;
                FreeHandle((HMMIO)pEnt);
                pEnt = gIOProcMapHead;
            }
        } else {
            pEntPrev = pEnt;
            pEnt = pEnt->pNext;
        }
     }
}



/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    UINT | mmioRename | This function renames the specified file.

@parm   LPCTSTR | szFilename | Specifies a pointer to a string
containing the filename of the file to rename.

@parm   LPCTSTR | szNewFileName | Specifies a pointer to a string
containing the new filename.

@parm   LPMMIOINFO | lpmmioinfo | Specifies a pointer to an
    <t MMIOINFO> structure containing extra parameters used by
    <f mmioRename>.

    If <p lpmmioinfo> is not NULL, all unused fields of the
    <t MMIOINFO> structure it references must be set to zero, including the
    reserved fields.

@parm   DWORD | dwRenameFlags | Specifies option flags for the rename
    operation.  This should be set to zero.

@rdesc  The return value is zero if the file was renamed.  Otherwise, the
return value is an error code returned from <f mmioRename> or from the I/O
procedure.
*/
/*--------------------------------------------------------------------*/
UINT APIENTRY
     mmioRenameW( LPCWSTR        szFileName
                , LPCWSTR        szNewFileName
                , LPCMMIOINFO    lpmmioinfo
                , DWORD          fdwRename
                )
{
    MMIOINFO    mmioinfo;

    ZeroMemory( &mmioinfo, sizeof( MMIOINFO ) );

    V_RPOINTER0(lpmmioinfo, sizeof(MMIOINFO), MMSYSERR_INVALPARAM);
    if (lpmmioinfo) {
        V_CALLBACK0((FARPROC)lpmmioinfo->pIOProc, MMSYSERR_INVALPARAM);
        mmioinfo = *lpmmioinfo;
    }

    SetIOProc(szFileName, &mmioinfo);

    if ( (mmioinfo.dwFlags & MMIO_UNICODEPROC )
      || (mmioinfo.pIOProc == mmioDOSIOProc )     // or the DOS file IO Proc
      || (mmioinfo.pIOProc == mmioMEMIOProc ) ) { // or a memory file IO Proc

        /*------------------------------------------------------------*\
         * We have an unicode IO Proc so use the given file names
         * without any conversion.
        \*------------------------------------------------------------*/
        return (UINT)IOProc( &mmioinfo, MMIOM_RENAME,
                       (LPARAM)szFileName, (LPARAM)szNewFileName );
    } else {

        UINT    uiRc;
        LPSTR   pAsciiFileName;      // Ascii version of szFileName
        LPSTR   pAsciiNewFileName;   // Ascii version of szNewFileName

        /*------------------------------------------------------------*\
         * We have an ascii IO Proc so convert the given file names
         * into ascii.
        \*------------------------------------------------------------*/
        pAsciiFileName = AllocAsciiStr( szFileName );
        if ( pAsciiFileName == (LPSTR)NULL ) {
            return MMIOERR_OUTOFMEMORY;
        }

        pAsciiNewFileName = AllocAsciiStr( szNewFileName );
        if ( pAsciiNewFileName == (LPSTR)NULL ) {
            FreeAsciiStr( pAsciiFileName );
            return MMIOERR_OUTOFMEMORY;
        }

        uiRc = (UINT)IOProc( &mmioinfo,
                       MMIOM_RENAME,
                       (LPARAM)pAsciiFileName,
                       (LPARAM)pAsciiNewFileName );

        FreeAsciiStr( pAsciiFileName );
        FreeAsciiStr( pAsciiNewFileName );

        return uiRc;
    }

}

UINT APIENTRY
     mmioRenameA( LPCSTR        szFileName
                , LPCSTR        szNewFileName
                , LPCMMIOINFO   lpmmioinfo
                , DWORD         fdwRename
                )
{
    MMIOINFO    mmioinfo;
    LPWSTR      pUnicodeFileName;
    LPWSTR      pUnicodeNewFileName;
    UINT        uiRc;

    ZeroMemory( &mmioinfo, sizeof( MMIOINFO ) );

    V_RPOINTER0(lpmmioinfo, sizeof(MMIOINFO), MMSYSERR_INVALPARAM);
    if (lpmmioinfo) {
        V_CALLBACK0((FARPROC)lpmmioinfo->pIOProc, MMSYSERR_INVALPARAM);
        mmioinfo = *lpmmioinfo;
    }

    /*----------------------------------------------------------------*\
     * SetIOProc only works with unicode strings, therefore we always
     * have to convert szFileName to unicode, so:
     * Allocate some storage to hold the unicode version of szFileName.
     * Do the acsii to unicode conversion .
     * Call SetIOProc
    \*----------------------------------------------------------------*/
    pUnicodeFileName = AllocUnicodeStr( szFileName );
    if ( pUnicodeFileName == (LPWSTR)NULL ) {
        return MMIOERR_OUTOFMEMORY;
    }
    SetIOProc( pUnicodeFileName, &mmioinfo );

    if ( (mmioinfo.dwFlags & MMIO_UNICODEPROC )
      || (mmioinfo.pIOProc == mmioDOSIOProc )     // or the DOS file IO Proc
      || (mmioinfo.pIOProc == mmioMEMIOProc ) ) { // or a memory file IO Proc

        /*------------------------------------------------------------*\
         * We have a unicode IO Proc, this means that we have to
         * convert szNewFileName to unicode too.
        \*------------------------------------------------------------*/
        pUnicodeNewFileName = AllocUnicodeStr( szNewFileName );
        if ( pUnicodeNewFileName == (LPWSTR)NULL ) {
            FreeUnicodeStr( pUnicodeFileName );
            return MMIOERR_OUTOFMEMORY;
        }

        uiRc = (UINT)IOProc( &mmioinfo,
                       MMIOM_RENAME,
                       (LPARAM)pUnicodeFileName,
                       (LPARAM)pUnicodeNewFileName );

        FreeUnicodeStr( pUnicodeNewFileName );

    } else {

        /*------------------------------------------------------------*\
         * We have an ascii IO Proc so use the given file names
         * without any conversion.
        \*------------------------------------------------------------*/
        uiRc = (UINT)IOProc( &mmioinfo, MMIOM_RENAME,
                       (LPARAM)szFileName, (LPARAM)szNewFileName);
    }

    FreeUnicodeStr( pUnicodeFileName );
    return uiRc;
}

/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    HMMIO | mmioOpen | This function opens a file for unbuffered
    or buffered I/O. The file can be a DOS file, a memory file, or an
    element of a custom storage system.

@parm   LPTSTR | szFilename | Specifies a pointer to a string
containing the filename of the file to open. If no I/O procedure is
specified to open the file, then the filename determines how the file
is opened, as follows:

    -- If the filename does not contain "+", then it is assumed
    to be the name of a DOS file.

    -- If the filename is of the form "foo.ext+bar", then the
    extension "EXT " is assumed to identify an installed I/O procedure
    which is called to perform I/O on the file (see <f mmioInstallIOProc>).

    -- If the filename is NULL and no I/O procedure is given, then
    <e MMIOINFO.adwInfo[0]> is assumed to be the DOS file handle
    of a currently open file.

    The filename should not be longer than 128 bytes, including the
    terminating NULL.

    When opening a memory file, set <p szFilename> to NULL.

@parm   LPMMIOINFO | lpmmioinfo | Specifies a pointer to an
    <t MMIOINFO> structure containing extra parameters used by
    <f mmioOpen>. Unless you are opening a memory file, specifying the
    size of a buffer for buffered I/O, or specifying an uninstalled I/O
    procedure to open a file, this parameter should be NULL.

    If <p lpmmioinfo> is not NULL, all unused fields of the
    <t MMIOINFO> structure it references must be set to zero, including the
    reserved fields.

@parm   DWORD | dwOpenFlags | Specifies option flags for the open
    operation. The MMIO_READ, MMIO_WRITE, and MMIO_READWRITE flags are
    mutually exclusive--only one should be specified. The MMIO_COMPAT,
    MMIO_EXCLUSIVE, MMIO_DENYWRITE, MMIO_DENYREAD, and MMIO_DENYNONE flags
    are DOS file-sharing flags, and can only be used after the DOS
    command SHARE has been executed.

    @flag   MMIO_READ | Opens the file for reading only.  This is the
        default, if MMIO_WRITE and MMIO_READWRITE are not specified.

    @flag   MMIO_WRITE | Opens the file for writing.  You should not
        read from a file opened in this mode.

    @flag   MMIO_READWRITE | Opens the file for both reading and writing.

    @flag   MMIO_CREATE | Creates a new file.
        If the file already exists, it is truncated to zero length.
        For memory files, MMIO_CREATE indicates the end of the file
        is initially at the start of the buffer.

    @flag   MMIO_DELETE | Deletes a file. If this flag is specified,
        <p szFilename> should not be NULL. The return
        value will be TRUE (cast to HMMIO) if the file was deleted
        successfully, FALSE otherwise.  Do not call <f mmioClose>
        for a file that has been deleted.  If this flag is specified,
        all other file opening flags are ignored.

    @flag   MMIO_PARSE | Creates a fully qualified filename from the path
        specified in <p szFileName>. The fully qualified filename is
        placed back into <p szFileName>. The return value
        will be TRUE (cast to HMMIO) if the qualification was
        successful, FALSE otherwise. The file is not opened, and the function
        does not return a valid MMIO file handle, so do not attempt to
        close the file. If this flag is specified, all other file
        opening flags are ignored.

    @flag   MMIO_EXIST | Determines whether the specified file exists
        and creates a fully qualified filename from the path
        specified in <p szFileName>. The fully qualified filename is
        placed back into <p szFileName>. The return value
        will be TRUE (cast to HMMIO) if the qualification was
        successful and the file exists, FALSE otherwise. The file is
        not opened, and the function does not return a valid MMIO file
        handle, so do not attempt to close the file.

    @flag   MMIO_ALLOCBUF | Opens a file for buffered I/O.
        To allocate a buffer larger or smaller than the default
        buffer size (8K), set the <e MMIOINFO.cchBuffer> field of the
        <t MMIOINFO> structure to the desired buffer size. If
        <e MMIOINFO.cchBuffer> is zero, then the default buffer size
        is used. If you are providing your own I/O buffer, then the
        MMIO_ALLOCBUF flag should not be used.

    @flag   MMIO_COMPAT | Opens the file with compatibility mode,
        allowing any process on a given machine to open the file
        any number of times.  <f mmioOpen> fails if the file has
        been opened with any of the other sharing modes.

    @flag   MMIO_EXCLUSIVE | Opens the file with exclusive mode,
        denying other processes both read and write access to the file.
        <f mmioOpen> fails if the file has been opened in any other
        mode for read or write access, even by the current process.

    @flag   MMIO_DENYWRITE | Opens the file and denies other
        processes write access to the file.  <f mmioOpen> fails
        if the file has been opened in compatibility or for write
        access by any other process.

    @flag   MMIO_DENYREAD | Opens the file and denies other
        processes read access to the file.  <f mmioOpen> fails if the
        file has been opened in compatibility mode or for read access
        by any other process.

    @flag   MMIO_DENYNONE | Opens the file without denying other
        processes read or write access to the file.  <f mmioOpen>
        fails if the file has been opened in compatibility mode
        by any other process.

    @flag   MMIO_GETTEMP | Creates a temporary filename, optionally
        using the parameters passed in <p szFileName> to determine
        the temporary name. For example, you can specify "C:F" to
        create a temporary file residing on drive C, starting with
        letter "F". The resulting filename is placed in the buffer
        pointed to by <p szFileName>.  The return value will be TRUE
        (cast to HMMIO) if the temporary filename was created successfully,
        FALSE otherwise. The file is
        not opened, and the function does not return a valid MMIO file
        handle, so do not attempt to close the file.
        This flag overrides all other flags.

@rdesc  The return value is a handle to the opened file. This handle
    is not a DOS file handle--do not use it with any file I/O functions
    other than MMIO functions.

    If the file cannot be opened, the return value is NULL.  If
    <p lpmmioinfo> is not NULL, then its <e MMIOINFO.wErrorRet> field
    will contain extended error information returned by the I/O
    procedure.

@comm   If <p lpmmioinfo> references an <t MMIOINFO> structure, set
up the fields as described below. All unused fields must be set to
zero, including reserved fields.

-- To request that a file be opened with an installed I/O
procedure, set the <e MMIOINFO.fccIOProc> field
to the four-character code of the I/O procedure,
and set the <e MMIOINFO.pIOProc> field to NULL.

-- To request that a file be opened with an uninstalled I/O procedure,
set the <e MMIOINFO.pIOProc> field to
point to the I/O procedure, and set <e MMIOINFO.fccIOProc> to NULL.

-- To request that <f mmioOpen> determine which I/O procedure to use
to open the file based on the filename contained in <p szFilename>,
set both <e MMIOINFO.fccIOProc> and <e MMIOINFO.pIOProc> to NULL.
This is the default behavior if no <t MMIOINFO> structure is specified.

-- To open a memory file using an internally allocated and managed
buffer, set the <e MMIOINFO.pchBuffer> field to NULL,
<e MMIOINFO.fccIOProc> to FOURCC_MEM,
<e MMIOINFO.cchBuffer> to the initial size of the buffer, and
<e MMIOINFO.adwInfo[0]> to the incremental expansion size of the
buffer. This memory file will automatically be expanded in increments of
<e MMIOINFO.adwInfo[0]> bytes when necessary. Specify the MMIO_CREATE
flag for the <p dwOpenFlags> parameter to initially set the end of
the file to be the beginning of the buffer.

-- To open a memory file using a caller-supplied buffer, set
the <e MMIOINFO.pchBuffer> field to point to the memory buffer,
<e MMIOINFO.fccIOProc> to FOURCC_MEM,
<e MMIOINFO.cchBuffer> to the size of the buffer, and
<e MMIOINFO.adwInfo[0]> to the incremental expansion size of the
buffer. The expansion size in <e MMIOINFO.adwInfo[0]> should only
be non-zero if <e MMIOINFO.pchBuffer> is a pointer obtained by calling
<f GlobalAlloc> and <f GlobalLock>, since <f GlobalReAlloc> will be called to
expand the buffer.  In particular, if <e MMIOINFO.pchBuffer> points to a
local or global array, a block of memory in the local heap, or a block
of memory allocated by <f GlobalDosAlloc>, <e MMIOINFO.adwInfo[0]> must
be zero.
Specify the MMIO_CREATE flag for the <p dwOpenFlags> parameter to
initially set the end of the file to be the beginning of the buffer;
otherwise, the entire block of memory will be considered readable.

-- To use a currently open DOS file handle with MMIO, set the
<e MMIOINFO.fccIOProc> field to FOURCC_DOS,
<e MMIOINFO.pchBuffer> to NULL, and <e MMIOINFO.adwInfo[0]> to the
DOS file handle.  Note that offsets within the file will be relative to
the beginning of the file, and will not depend on the DOS file position
at the time <f mmioOpen> is called; the initial MMIO offset will be the same
as the DOS offset when <f mmioOpen> is called.
Later, to close the MMIO file handle without closing the DOS
file handle, pass the MMIO_FHOPEN flag to <f mmioClose>.

You must call <f mmioClose> to close a file opened with <f mmioOpen>.
Open files are not automatically closed when an application exits.

@xref   mmioClose
*/

/* these are the changes to mmioOpen() to support compound files... */

/* @doc CFDOC

@api    HMMIO | mmioOpen | ...The file can be a DOS file, a memory file,
    an element of a RIFF compound file...

@parm   LPTSTR | szFilename | ...

    -- If <p szFilename> is of the form "foo+bar", then <f mmioOpen>
    opens the compound file element named "bar" that is stored inside
    the RIFF compound file named "foo".

    -- If <p szFilename> is of the form "foo.ext+bar", then the
    extension "ext" is assumed to identify the installed I/O procedure
    (see <f mmioInstallIOProc>).  The extension "bnd", and any extensions
    that have not been installed, are assumed to refer to a RIFF compound
    file.

@parm   LPMMIOINFO | lpmmioinfo | ...

@parm   DWORD | dwOpenFlags | ...

@rdesc  ...

@comm   ...

    The following I/O procedure identifiers (type FOURCC) are predefined:

    ...

    FOURCC_BND: <p szFilename> is assumed to be the name of
    a RIFF compound file element, and <p adwInfo[0]> should
    contain the HMMCF of the compound file.  Alternatively,
    <p szFilename> can include the name of the compound file
    (e.g. "foo.bnd+bar.dib" as described above), and <p adwInfo[0]>
    should be NULL, to automatically open the compound file.

    ...

    The easy way to open an element of a RIFF compound file: just
    include the name of the compound file in <p szFilename> preceded
    by a "+" as described above.  For example, opening
    "c:\data\bar.bnd+blorg.dib" opens the compound file element
    named "blorg.dib" in the compound file "c:\data\bar.bnd".
    <p lpmmioinfo> can be null in this case -- set <p dwOpenFlags>
    as described above.  You can use this same method to open an
    element of a custom storage system, if the file extension of the
    compound file ("bnd" in the above example) corresponds to an
    installed I/O procedure -- see <f mmioInstallIOProc> for details.

    To open an element of a RIFF compound file that was opened using
    <f mmioCFAccess> or <f mmioCFOpen>: set <p szFilename>
    to be the name of the compound file element; set <p fccIOProc>
    to FOURCC_BND; set <p adwInfo[0]> to the HMMCF of the open compound
    file; set <p dwOpenFlags> and <p cchBuffer> as described above;
    set all other fields of <p lpmmioinfo> to zero.

    ...
*/
/*--------------------------------------------------------------------*/
HMMIO APIENTRY
      mmioOpenW( LPWSTR szFileName, LPMMIOINFO lpmmioinfo, DWORD dwOpenFlags )
{
    PMMIO       pmmio;      // MMIO status block
    LPSTR       hpBuffer;
    UINT        w;          // an MMRESULT or a LRESULT from an IOPROC

    V_FLAGS(dwOpenFlags, MMIO_OPEN_VALID, mmioOpen, NULL);
    V_WPOINTER0(lpmmioinfo, sizeof(MMIOINFO), NULL);

    if (lpmmioinfo) {
        lpmmioinfo->wErrorRet = 0;
        V_CALLBACK0((FARPROC)lpmmioinfo->pIOProc, NULL);
    }

    /* allocate MMIO status information block */
    if ( (pmmio = (PMMIO)(NewHandle(TYPE_MMIO, NULL, sizeof(MMIOINFO)))) == NULL)
    {
        if (lpmmioinfo) {
            lpmmioinfo->wErrorRet = MMIOERR_OUTOFMEMORY;
        }
        return NULL;
    }

    //  Implicitly acquired by NewHandle()
    ReleaseHandleListResource();

    /*----------------------------------------------------------------*\
     * NewHandle does not zero the allocated storage so we had better do
     * it now.
    \*----------------------------------------------------------------*/
    ZeroMemory( pmmio, sizeof(MMIOINFO) );

    /* if user supplied <lpmmioinfo>, copy it to <pmmio> */
    if (lpmmioinfo != NULL) {
        *pmmio = *lpmmioinfo;
    }

    /* <dwOpenFlags> always takes precedence over contents of <pmmio> */
    pmmio->dwFlags = dwOpenFlags;
    pmmio->hmmio = ((HMMIO)pmmio);

    /* MMIO_ALLOCBUF in the flags means that the user wants a buffer
     * allocated for buffered I/O, but after this point it means that
     * a buffer *was* allocated, so turn off the flag until the buffer
     * is actually allocated (which is done by mmioSetBuffer() below)
     */
    if (pmmio->dwFlags & MMIO_ALLOCBUF)
    {
        /* if a buffer size is not specified, use the default */
        if (pmmio->cchBuffer == 0) {
            pmmio->cchBuffer = MMIO_DEFAULTBUFFER;
        }
        pmmio->dwFlags &= ~MMIO_ALLOCBUF;
    }

    /* Set the pIOProc function as determined by the file name or the
     * parameters in the pmmio structure.
     */
    SetIOProc(szFileName, pmmio);

    /* The pmmio structure hasn't been set up for buffering, so we must
     * explicitly make sure that pchBuffer is NULL.
     */
    hpBuffer = pmmio->pchBuffer;
    pmmio->pchBuffer = NULL;

    /* set up buffered I/O however the user requested it */
    w = mmioSetBuffer(((HMMIO)pmmio), hpBuffer, pmmio->cchBuffer, 0);
    if (w)
    {
        if (lpmmioinfo) {
            lpmmioinfo->wErrorRet = w;
        }
        FreeHandle(((HMMIO)pmmio));
        return NULL;
    }

    if ( (pmmio->dwFlags & MMIO_UNICODEPROC)    // a Unicode IO Proc
      || (pmmio->pIOProc == mmioDOSIOProc )     // or the DOS file IO Proc
      || (pmmio->pIOProc == mmioMEMIOProc ) ) { // or a memory file IO Proc

        /* let the I/O procedure open/delete/qualify the file */
        w = (UINT)IOProc( pmmio, MMIOM_OPEN, (LPARAM)szFileName, 0L );

    } else {

        if (NULL == szFileName) {

            w = (UINT)IOProc( pmmio,
                        MMIOM_OPEN,
                        (LPARAM)NULL,
                        0L );

        } else {
            LPSTR   lpAsciiFileName;  // ascii version of szFileName

            /*------------------------------------------------------------*\
            * We have an ascii IO Proc so convert the given file name
            * into ascii.
            \*------------------------------------------------------------*/
            lpAsciiFileName = AllocAsciiStr( szFileName );
            if ( lpAsciiFileName == (LPSTR)NULL ) {
                if (lpmmioinfo) {
                    lpmmioinfo->wErrorRet = MMIOERR_OUTOFMEMORY;
                }
                FreeHandle( (HMMIO)pmmio );
                return NULL;
            }

            /*------------------------------------------------------------*\
            * Call the IO proc and then free the allocated unicode
            * filename storage.
            \*------------------------------------------------------------*/
            w = (UINT)IOProc( pmmio,
                        MMIOM_OPEN,
                        (LPARAM)lpAsciiFileName,
                        0L );

            FreeAsciiStr( lpAsciiFileName );
        }
    }

    /* If this is non-zero, return it to the user */
    if (w != 0)
    {
        if (lpmmioinfo != NULL) {
            lpmmioinfo->wErrorRet = w;
        }
        FreeHandle(((HMMIO)pmmio));
        return NULL;
    }

    if (pmmio->dwFlags & (MMIO_DELETE| MMIO_PARSE| MMIO_EXIST| MMIO_GETTEMP))
    {
        /* if the file is being deleted/parsed/name gotten, exit
         * QUICKLY because the file handle (or whatever) in <pmmio>
         * is not valid.
         */
        mmioSetBuffer(((HMMIO)pmmio), NULL, 0L, 0);
        FreeHandle(((HMMIO)pmmio));
        return (HMMIO) TRUE;
    }

    /* the initial "current buffered offset" will be equal to the initial
     * "current disk offset"
     */
    pmmio->lBufOffset = pmmio->lDiskOffset;

    return ((HMMIO)pmmio);
}

HMMIO APIENTRY
      mmioOpenA( LPSTR szFileName, LPMMIOINFO lpmmioinfo, DWORD dwOpenFlags )
{
    PMMIO       pmmio;          // MMIO status block
    LPSTR       hpBuffer;
    UINT        w;              // an MMRESULT or a LRESULT from an IOPROC
    LPWSTR      lpUnicodeName;  // Unicode version of szFileName
    WCHAR       UnicodeBuffer[ MAX_PATH ];


    V_FLAGS(dwOpenFlags, MMIO_OPEN_VALID, mmioOpen, NULL);
    V_WPOINTER0(lpmmioinfo, sizeof(MMIOINFO), NULL);

    if (lpmmioinfo) {
        lpmmioinfo->wErrorRet = 0;
        V_CALLBACK0((FARPROC)lpmmioinfo->pIOProc, NULL);
    }

    /*----------------------------------------------------------------*\
     * Don't convert szFilename if it does not point to anything
    \*----------------------------------------------------------------*/
    if ( szFileName != (LPSTR)NULL ) {

        /*----------------------------------------------------------------*\
         * Convert the Ascii szFileName to Unicode
        \*----------------------------------------------------------------*/
        AsciiStrToUnicodeStr( (PBYTE)UnicodeBuffer,
                              (PBYTE)UnicodeBuffer + (MAX_PATH * sizeof(WCHAR)),
                              szFileName );
        lpUnicodeName = UnicodeBuffer;

    } else {
        lpUnicodeName = (LPWSTR)NULL;
    }


    /* allocate MMIO status information block */
    if ( (pmmio = (PMMIO)(NewHandle(TYPE_MMIO, NULL, sizeof(MMIOINFO)))) == NULL)
    {
        if (lpmmioinfo) {
            lpmmioinfo->wErrorRet = MMIOERR_OUTOFMEMORY;
        }
        return NULL;
    }
    
    //  Implicitly acquired by NewHandle()
    ReleaseHandleListResource();

    /*----------------------------------------------------------------*\
     * NewHandle does not zero the allocated storage so we had better do
     * it now.
    \*----------------------------------------------------------------*/
    ZeroMemory( pmmio, sizeof(MMIOINFO) );

    /* if user supplied <lpmmioinfo>, copy it to <pmmio> */
    if (lpmmioinfo != NULL) {
        *pmmio = *lpmmioinfo;
    }

    /* <dwOpenFlags> always takes precedence over contents of <pmmio> */
    pmmio->dwFlags = dwOpenFlags;
    pmmio->hmmio = ((HMMIO)pmmio);

    /* MMIO_ALLOCBUF in the flags means that the user wants a buffer
     * allocated for buffered I/O, but after this point it means that
     * a buffer *was* allocated, so turn off the flag until the buffer
     * is actually allocated (which is done by mmioSetBuffer() below)
     */
    if (pmmio->dwFlags & MMIO_ALLOCBUF)
    {
        /* if a buffer size is not specified, use the default */
        if (pmmio->cchBuffer == 0) {
            pmmio->cchBuffer = MMIO_DEFAULTBUFFER;
        }
        pmmio->dwFlags &= ~MMIO_ALLOCBUF;
    }

    /* Set the pIOProc function as determined by the file name or the
     * parameters in the pmmio structure.
     */
    SetIOProc( lpUnicodeName, pmmio );

    /* The pmmio structure hasn't been set up for buffering, so we must
     * explicitly make sure that pchBuffer is NULL.
     */
    hpBuffer = pmmio->pchBuffer;
    pmmio->pchBuffer = NULL;

    /* set up buffered I/O however the user requested it */
    w = mmioSetBuffer(((HMMIO)pmmio), hpBuffer, pmmio->cchBuffer, 0);
    if (w)
    {
        if (lpmmioinfo) {
            lpmmioinfo->wErrorRet = w;
        }
        FreeHandle(((HMMIO)pmmio));
        return NULL;
    }

    if ( (pmmio->dwFlags & MMIO_UNICODEPROC)        // a Unicode IO Proc
        || (pmmio->pIOProc == mmioDOSIOProc)        // or the DOS file IO Proc
        || (pmmio->pIOProc == mmioMEMIOProc) ) {    // or a memory file IO Proc

        /* let the I/O procedure open/delete/qualify the file */
        w = (UINT)IOProc( pmmio, MMIOM_OPEN,
                    (LPARAM)lpUnicodeName, 0L );

        /*------------------------------------------------------------*\
         * If we have a DOS IO proc and the user specified the
         * parse option and we did not get any errors from the IO proc
         * call we convert the returned parsed path string from Unicode
         * back into Ansi and copy this value into szFileName.
        \*------------------------------------------------------------*/
        if ( w == 0
          && (pmmio->pIOProc == mmioDOSIOProc)
          && ((dwOpenFlags & MMIO_PARSE) || (dwOpenFlags & MMIO_GETTEMP)) ) {

              BYTE   ansiPath[ MAX_PATH ];

              UnicodeStrToAsciiStr( ansiPath,
                                    ansiPath + MAX_PATH,
                                    lpUnicodeName );
              strcpy( (LPSTR)szFileName, (LPCSTR)ansiPath );
        }

    } else {

        w = (UINT)IOProc( pmmio, MMIOM_OPEN, (LPARAM)szFileName, 0L );

    }

    /* If this is non-zero, return it to the user */
    if (w != 0)
    {
        if (lpmmioinfo != NULL) {
            lpmmioinfo->wErrorRet = w;
        }
        FreeHandle(((HMMIO)pmmio));
        return NULL;
    }

    if (pmmio->dwFlags & (MMIO_DELETE| MMIO_PARSE| MMIO_EXIST| MMIO_GETTEMP))
    {
        /* if the file is being deleted/parsed/name gotten, exit
         * QUICKLY because the file handle (or whatever) in <pmmio>
         * is not valid.
         */
        mmioSetBuffer(((HMMIO)pmmio), NULL, 0L, 0);
        FreeHandle(((HMMIO)pmmio));
        return (HMMIO) TRUE;
    }

    /* the initial "current buffered offset" will be equal to the initial
     * "current disk offset"
     */
    pmmio->lBufOffset = pmmio->lDiskOffset;

    return ((HMMIO)pmmio);
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    MMRESULT | mmioClose | This function closes a file opened with
    <f mmioOpen>.

@parm   HMMIO | hmmio | Specifies the file handle of the file to
    close.

@parm   UINT | uFlags | Specifies options for the close operation.

    @flag   MMIO_FHOPEN | If the file was opened by passing the DOS
        file handle of an already-opened file to <f mmioOpen>, then
        using this flag tells <f mmioClose> to close the MMIO file
        handle, but not the DOS file handle.  (This is done by the
        I/O Proc).

@rdesc  The return value is zero if the function is successful.
    Otherwise, the return value is an error code, either from
    <f mmioFlush> or from the I/O procedure. The error code can be
    one of the following codes:

    @flag MMIOERR_CANNOTWRITE | The contents of the buffer could
    not be written to disk.

    @flag MMIOERR_CANNOTCLOSE | There was a DOS file system error when
    the I/O Proc attempted to close the DOS file.

@xref   mmioOpen mmioFlush
*/
/*--------------------------------------------------------------------*/
MMRESULT APIENTRY
        mmioClose(HMMIO hmmio, UINT uFlags)
{
    UINT w;                /* either an LRESULT from an IOProc or an MMRESULT */

    V_HANDLE(hmmio, TYPE_MMIO, MMSYSERR_INVALHANDLE);

    if ((w = mmioFlush(hmmio, 0)) != 0)
        return w;

    w = (UINT)IOProc( (PMMIO)hmmio, MMIOM_CLOSE, (LPARAM)(DWORD) uFlags, (LPARAM) 0);
    if (w != 0) return w;

    /* free the buffer if necessary */
    mmioSetBuffer(hmmio, NULL, 0L, 0);

        FreeHandle(hmmio);

    return 0;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    LRESULT | mmioRead | This function reads a specified number of
    bytes from a file opened with <f mmioOpen>.

@parm   HMMIO | hmmio | Specifies the file handle of the file to be
    read.

@parm   LPSTR | pch | Specifies a pointer to a buffer to contain
    the data read from the file.

@parm   LONG | cch | Specifies the number of bytes to read from the
    file.

@rdesc  The return value is the number of bytes actually read. If the
    end of the file has been reached and no more bytes can be read, the
    return value is zero. If there is an error reading from the file, the
    return value is -1.

@comm  On 16 bit windows pch is a huge pointer.  On 32 bit windows there is no
    distinction between huge pointers and long pointers.

@xref   mmioWrite
*/
/*--------------------------------------------------------------------*/
LONG APIENTRY
mmioRead(HMMIO hmmio, LPSTR pch, LONG cch)
{
    LONG        lTotalBytesRead = 0L;   // total no. bytes read
    LONG        lBytes;         // no. bytes that can be read
    PMMIO       pmmio=(PMMIO)hmmio; //local copy hmmio - avoid casting, simplify debug

    V_HANDLE(hmmio, TYPE_MMIO, -1);
    V_WPOINTER(pch, cch, -1);

    for(;;)
    {
        /* calculate the number of bytes that can be read */
        lBytes = (LONG)(pmmio->pchEndRead - pmmio->pchNext);

        /* can only read at most <cch> bytes from buffer */
        if (lBytes > cch)
            lBytes = cch;

        if (lBytes > 0)
        {
            /* this is where some performance improvements can
             * be made, especially for small reads...?
             */
            CopyMemory(pch, pmmio->pchNext, lBytes);
            pmmio->pchNext += lBytes;
            pch += lBytes;
            cch -= lBytes;
            lTotalBytesRead += lBytes;
        }

        /* cannot do MMIOM_READ from memory files */
        if (pmmio->fccIOProc == FOURCC_MEM)
            return lTotalBytesRead;

        if (cch == 0)           // no more to read?
            return lTotalBytesRead;

        /* we need to read beyond this buffer; if we have at least
         * another bufferful to read, just call the I/O procedure
         */
        if (cch > pmmio->cchBuffer)
            break;

        /* read the next bufferful and loop around */
        if (mmioAdvance(hmmio, NULL, MMIO_READ) != 0)
            return -1;

        /* if mmioAdvance() couldn't read any more data, we must be
         * at the end of the file
         */
        if (pmmio->pchNext == pmmio->pchEndRead)
            return lTotalBytesRead;
    }

    /* flush and empty the I/O buffer and manipulate <lBufOffset>
     * directly to change the current file position
     */
    if (mmioFlush(hmmio, MMIO_EMPTYBUF) != 0)
        return -1;

    /* call the I/O procedure to do the rest of the reading */
    lBytes = mmioDiskIO(pmmio, MMIOM_READ, pch, cch);
    pmmio->lBufOffset = pmmio->lDiskOffset;

    return (lBytes == -1L) ? -1L : lTotalBytesRead + lBytes;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    LRESULT | mmioWrite | This function writes a specified number of
    bytes to a file opened with <f mmioOpen>.

@parm   HMMIO | hmmio | Specifies the file handle of the file.

@parm   LPSTR | pch | Specifies a pointer to the buffer to be
    written to the file.

@parm   LONG | cch | Specifies the number of bytes to write to the
    file.

@rdesc  The return value is the number of bytes actually written. If
    there is an error writing to the file, the return value is -1.

@comm   The current file position is incremented by the number of
    bytes written.   On 16 bit windows pch is a huge pointer.
    On 32 bit windows there is no distinction between huge pointers
    and long pointers.

@xref   mmioRead
*/
/*--------------------------------------------------------------------*/
LONG APIENTRY
mmioWrite(HMMIO hmmio, LPCSTR pch, LONG cch)
{
    LONG        lTotalBytesWritten = 0L; // total no. bytes written
    LONG        lBytes;         // no. bytes that can be written
    // "pch" is LPCSTR which is correct, but
    // we pass it to a polymorphic routine
    // which needs LPSTR.

    V_HANDLE(hmmio, TYPE_MMIO, -1);
    V_RPOINTER(pch, cch, -1);

    for(;;)
    {
        /* calculate the number of bytes that can be written */
        lBytes = (LONG)(((PMMIO)hmmio)->pchEndWrite - ((PMMIO)hmmio)->pchNext);

        if ((cch > lBytes) && (((PMMIO)hmmio)->fccIOProc == FOURCC_MEM))
        {
            /* this is a memory file -- expand it */
            if (mmioExpandMemFile(((PMMIO)hmmio), cch - lBytes) != 0)
                return -1;  // cannot expand
            lBytes = (LONG)(((PMMIO)hmmio)->pchEndWrite - ((PMMIO)hmmio)->pchNext);
        }

        /* can only write at most <cch> bytes into the buffer */
        if (lBytes > cch)
            lBytes = cch;

        /* this is where some performance improvements can
         * be made, especially for small writes... should
         * special-case cases when segment boundaries are
         * not crossed (or maybe hmemcpy() should do that)
         */
        if (lBytes > 0)
        {
            CopyMemory(((PMMIO)hmmio)->pchNext, pch, lBytes);
            ((PMMIO)hmmio)->dwFlags |= MMIO_DIRTY;
            ((PMMIO)hmmio)->pchNext += lBytes;
            pch += lBytes;
            cch -= lBytes;
            lTotalBytesWritten += lBytes;
        }

        /* validate <pchEndRead>, i.e. re-enforce the invariant that
         * <pchEndRead> points past the last valid byte in the buffer
         */
        if (((PMMIO)hmmio)->pchEndRead < ((PMMIO)hmmio)->pchNext)
            ((PMMIO)hmmio)->pchEndRead = ((PMMIO)hmmio)->pchNext;

        if (cch == 0)           // no more to write?
            return lTotalBytesWritten;

        /* we need to read beyond this buffer; if we have at least
         * another bufferful to read, just call the I/O procedure
         */
        if (cch > ((PMMIO)hmmio)->cchBuffer)
            break;

        /* write this buffer (if needed) and read the next
         * bufferful (if needed)
         */
        if (mmioAdvance(hmmio, NULL, MMIO_WRITE) != 0)
            return -1;
    }

    /* we should never need to do MMIOM_WRITE with memory files */

    /* flush and empty the I/O buffer and manipulate <lBufOffset>
     * directly to change the current file position
     */
    if (mmioFlush(hmmio, MMIO_EMPTYBUF) != 0)
        return -1;

    /* call the I/O procedure to do the rest of the writing
     * mmioDiskIO is a polymorphic routine, hence we need to cast
     * our LPCSTR input pointer to LPSTR.
     */
    lBytes = mmioDiskIO(((PMMIO)hmmio), MMIOM_WRITE, (LPSTR)pch, cch);
    ((PMMIO)hmmio)->lBufOffset = ((PMMIO)hmmio)->lDiskOffset;

    return (lBytes == -1L) ? -1L : lTotalBytesWritten + lBytes;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    LRESULT | mmioSeek | This function changes the current file
    position in a file opened with <f mmioOpen>. The current file
    position is the location in the file where data is read or written.

@parm   HMMIO | hmmio | Specifies the file handle of the file to seek
    in.

@parm   LONG | lOffset | Specifies an offset to change the file position.

@parm   int | iOrigin | Specifies how the offset specified by
    <p lOffset> is interpreted. Contains one of the following flags:

    @flag   SEEK_SET | Seeks to <p lOffset> bytes from the beginning
        of the file.

    @flag   SEEK_CUR | Seeks to <p lOffset> bytes from the current
        file position.

    @flag   SEEK_END | Seeks to <p lOffset> bytes from the end
        of the file.

@rdesc  The return value is the new file position in bytes, relative
    to the beginning of the file. If there is an error, the return value
    is -1.

@comm   Seeking to an invalid location in the file, such as past the
    end of the file, may cause <f mmioSeek> to not return an error,
    but may cause subsequent I/O operations on the file to fail.

    To locate the end of a file, call <f mmioSeek> with <p lOffset>
    set to zero and <p iOrigin> set to SEEK_END.
*/
/*--------------------------------------------------------------------*/
LONG APIENTRY
mmioSeek(HMMIO hmmio, LONG lOffset, int iOrigin)
{
    LONG        lCurOffset; // disk offset of <pchNext>
    LONG        lEndBufOffset;  // disk offset of end of buffer
    LONG        lNewOffset; // new disk offset

    V_HANDLE(hmmio, TYPE_MMIO, -1);

    /* careful! all this buffer pointer manipulation is fine, but keep
     * in mind that buffering may be disabled (in which case <pchEndRead>
     * and <pchBuffer> will both be NULL, so the buffer will appear to
     * be zero bytes in size)
     */

    /* <((PMMIO)hmmio)->lBufOffset> is the disk offset of the start of the
     * start of the buffer; determine <lCurOffset>, the offset of <pchNext>,
     * and <lEndBufOffset>, the offset of the end of the valid part
     * of the buffer
     */
    lCurOffset = (LONG)(((PMMIO)hmmio)->lBufOffset +
        (((PMMIO)hmmio)->pchNext - ((PMMIO)hmmio)->pchBuffer));
    lEndBufOffset = (LONG)(((PMMIO)hmmio)->lBufOffset +
        (((PMMIO)hmmio)->pchEndRead - ((PMMIO)hmmio)->pchBuffer));

    /* determine <lNewOffset>, the offset to seek to */
    switch (iOrigin)
    {
    case SEEK_SET:      // seek relative to start of file

        lNewOffset = lOffset;
        break;

    case SEEK_CUR:      // seek relative to current location

        lNewOffset = lCurOffset + lOffset;
        break;

    case SEEK_END:      // seek relative to end of file

        if (((PMMIO)hmmio)->fccIOProc == FOURCC_MEM)
            lNewOffset = lEndBufOffset - lOffset;
        else
        {
            LONG    lEndFileOffset;

            /* find out where the end of the file is */
            lEndFileOffset
                 = (LONG)IOProc( (PMMIO)hmmio, MMIOM_SEEK, (LPARAM) 0, (LPARAM) SEEK_END);
            if (lEndFileOffset == -1)
                return -1;
            /* Check that we don't have buffered data not yet written */

            if (lEndBufOffset > lEndFileOffset) {
                lEndFileOffset = lEndBufOffset;
            }

            lNewOffset = lEndFileOffset - lOffset;
        }
        break;
    default: lNewOffset = 0;
        {
          dprintf(( "Invalid seek type %d\n",iOrigin));
          WinAssert(FALSE);
        }
    }

    if ( (lNewOffset >= ((PMMIO)hmmio)->lBufOffset)
       && (lNewOffset <= lEndBufOffset)
       )
    {
        /* seeking within the valid part of the buffer
         * (possibly including seeking to <lEndBufOffset>)
         */
        ((PMMIO)hmmio)->pchNext = ((PMMIO)hmmio)->pchBuffer +
            (lNewOffset - ((PMMIO)hmmio)->lBufOffset);
    }
    else
    {
        /* seeking outside the buffer */
        if (((PMMIO)hmmio)->fccIOProc == FOURCC_MEM)
            return -1;  // can't seek outside mem. file buffer
        if (mmioFlush(hmmio, 0) != 0)
            return -1;

        /* the current "buffered file position" (same as <lDiskOffset>
         * for unbuffered files) equals <lBufOffset> +
         * (<pchNext> - <pchBuffer>); we'll move the current buffered
         * file position (and empty the buffer, since it becomes
         * invalid when <lBufOffset> changes) as follows...
         */
        ((PMMIO)hmmio)->lBufOffset = lNewOffset;
        ((PMMIO)hmmio)->pchNext
            = ((PMMIO)hmmio)->pchEndRead
            = ((PMMIO)hmmio)->pchBuffer;

        /* don't need to actually seek right now, since the next
         * MMIOM_READ or MMIOM_WRITE will have to seek anyway
         */
    }

    return lNewOffset;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    MMRESULT | mmioGetInfo | This function retrieves information
    about a file opened with <f mmioOpen>. This information allows the
    caller to directly access the I/O buffer, if the file is opened
    for buffered I/O.

@parm   HMMIO | hmmio | Specifies the file handle of the file.

@parm   LPMMIOINFO | lpmmioinfo | Specifies a pointer to a
    caller-allocated <t MMIOINFO> structure that <f mmioGetInfo>
    fills with information about the file. See the <t MMIOINFO> structure
    and the <f mmioOpen> function for information about the fields in
    this structure.

@parm   UINT | uFlags | Is not used and should be set to zero.

@rdesc  The return value is zero if the function is successful.

@comm   To directly access the I/O buffer of a file opened for
    buffered I/O, use the following fields of the <t MMIOINFO> structure
    filled by <f mmioGetInfo>:

    -- The <e MMIOINFO.pchNext> field points to the next byte in the
    buffer that can be read or written. When you read or write, increment
    <e MMIOINFO.pchNext> by the number of bytes read or written.

    -- The <e MMIOINFO.pchEndRead> field points to one byte past the
    last valid byte in the buffer that can be read.

    -- The <e MMIOINFO.pchEndWrite> field points to one byte past the
    last location in the buffer that can be written.

    Once you read or write to the buffer and modify
    <e MMIOINFO.pchNext>, do not call any MMIO function except
    <f mmioAdvance> until you call <f mmioSetInfo>. Call <f mmioSetInfo>
    when you are finished directly accessing the buffer.

    When you reach the end of the buffer specified by
    <e MMIOINFO.pchEndRead> or <e MMIOINFO.pchEndWrite>, call
    <f mmioAdvance> to fill the buffer from the disk, or write
    the buffer to the disk. The <f mmioAdvance> function
    will update the <e MMIOINFO.pchNext>, <e MMIOINFO.pchEndRead>, and
    <e MMIOINFO.pchEndWrite> fields in the <t MMIOINFO> structure for the
    file.

    Before calling <f mmioAdvance> or <f mmioSetInfo> to flush a
    buffer to disk, set the MMIO_DIRTY flag in the <e MMIOINFO.dwFlags>
    field of the <t MMIOINFO> structure for the file. Otherwise, the
    buffer will not get written to disk.

    Do not decrement <e MMIOINFO.pchNext> or modify any fields in the
    <t MMIOINFO> structure other than <e MMIOINFO.pchNext> and
    <e MMIOINFO.dwFlags>. Do not set any flags in <e MMIOINFO.dwFlags>
    except MMIO_DIRTY.

@xref   mmioSetInfo MMIOINFO
*/
/*--------------------------------------------------------------------*/
MMRESULT APIENTRY
mmioGetInfo(HMMIO hmmio, LPMMIOINFO lpmmioinfo, UINT uFlags)
{
    V_HANDLE(hmmio, TYPE_MMIO, MMSYSERR_INVALHANDLE);
    V_WPOINTER(lpmmioinfo, sizeof(MMIOINFO), MMSYSERR_INVALPARAM);

    *lpmmioinfo = *((PMMIO)hmmio);

    return 0;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    MMRESULT | mmioSetInfo | This function updates the information
    retrieved by <f mmioGetInfo> about a file opened with <f mmioOpen>.
    Use this function to terminate direct buffer access of a file opened
    for buffered I/O.

@parm   HMMIO | hmmio | Specifies the file handle of the file.

@parm   LPMMIOINFO | lpmmioinfo | Specifies a pointer to an
    <t MMIOINFO> structure filled with information with
    <f mmioGetInfo>.

@parm   UINT | uFlags | Is not used and should be set to zero.

@rdesc  The return value is zero if the function is successful.

@comm   If you have written to the file I/O buffer, set the
    MMIO_DIRTY flag in the <e MMIOINFO.dwFlags> field of the <t MMIOINFO>
    structure before calling <f mmioSetInfo> to terminate direct buffer
    access. Otherwise, the buffer will not get flushed to disk.

@xref   mmioGetInfo MMIOINFO
*/
/*--------------------------------------------------------------------*/
MMRESULT APIENTRY
mmioSetInfo(HMMIO hmmio, LPCMMIOINFO lpmmioinfo, UINT fuInfo)
{
    V_HANDLE(hmmio, TYPE_MMIO, MMSYSERR_INVALHANDLE);
    V_RPOINTER(lpmmioinfo, sizeof(MMIOINFO), MMSYSERR_INVALPARAM);
    V_RPOINTER0( lpmmioinfo->pchBuffer
               , lpmmioinfo->cchBuffer
               , MMSYSERR_INVALPARAM
               );
    V_CALLBACK((FARPROC)lpmmioinfo->pIOProc, MMSYSERR_INVALPARAM);

    /* copy the relevant information from <lpmmioinfo> back into <hmmio> */
    *((PMMIO)hmmio) = *lpmmioinfo;

    /* validate <pchEndRead>, i.e. re-enforce the invariant that
     * <pchEndRead> points past the last valid byte in the buffer
     */
    if (((PMMIO)hmmio)->pchEndRead < ((PMMIO)hmmio)->pchNext)
        ((PMMIO)hmmio)->pchEndRead = ((PMMIO)hmmio)->pchNext;

    return 0;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    MMRESULT | mmioSetBuffer | This function enables or disables
    buffered I/O, or changes the buffer or buffer size for a file opened
    with <f mmioOpen>.

@parm   HMMIO | hmmio | Specifies the file handle of the file.

@parm   LPSTR | pchBuffer | Specifies a pointer to a
    caller-supplied buffer to use for buffered I/O. If NULL,
    <f mmioSetBuffer> allocates an internal buffer for buffered I/O.

@parm   LONG | cchBuffer | Specifies the size of the caller-supplied
    buffer, or the size of the buffer for <f mmioSetBuffer> to allocate.

@parm   UINT | fuInfo | Is not used and should be set to zero.

@rdesc  The return value is zero if the function is successful.
    Otherwise, the return value specifies an error code. If an error
    occurs, the file handle remains valid. The error code can be one
    of the following codes:

    @flag MMIOERR_CANNOTWRITE | The contents of the old buffer could
    not be written to disk, so the operation was aborted.

    @flag MMIOERR_OUTOFMEMORY | The new buffer could not be allocated,
    probably due to a lack of available memory.

@comm   To enable buffering using an internal buffer, set
    <p pchBuffer> to NULL and <p cchBuffer> to the desired buffer size.

    To supply your own buffer, set <p pchBuffer> to point to the buffer,
    and set <p cchBuffer> to the size of the buffer.

    To disable buffered I/O, set <p pchBuffer> to NULL and
    <p cchBuffer> to zero.

    If buffered I/O is already enabled using an internal buffer, you
    can reallocate the buffer to a different size by setting
    <p pchBuffer> to NULL and <p cchBuffer> to the new buffer size. The
    contents of the buffer may be changed after resizing.
 */
/*--------------------------------------------------------------------*/
MMRESULT APIENTRY
         mmioSetBuffer( HMMIO hmmio
                      , LPSTR pchBuffer
                      , LONG cchBuffer
                      , UINT uFlags
                      )
{
    MMRESULT mmr;
    HANDLE hMem;

    V_HANDLE(hmmio, TYPE_MMIO, MMSYSERR_INVALHANDLE);
    // Validate the buffer - for READ/WRITE as appropriate
    if (((PMMIO)hmmio)->dwFlags & MMIO_WRITE) {
	V_WPOINTER0(pchBuffer, cchBuffer, MMSYSERR_INVALPARAM);
    } else {
	V_RPOINTER0(pchBuffer, cchBuffer, MMSYSERR_INVALPARAM);
    }

    if ((((PMMIO)hmmio)->dwFlags & MMIO_ALLOCBUF) &&
        (pchBuffer == NULL) && (cchBuffer > 0))
    {
        /* grow or shrink buffer in-place */
        LPSTR       pch;
        LONG        lDeltaNext;
        LONG        lDeltaEndRead;

        /* Since the ALLOCBUF flag is set, we must have a buffer */

        /* write the buffer to disk, but don't empty it */
        if ((mmr = mmioFlush(hmmio, 0)) != 0)
            return mmr;

        for(;;)
        {
            /* remember where <pchNext> and <pchEndRead> are
             * in the buffer
             */
            lDeltaNext = (LONG)(((PMMIO)hmmio)->pchNext - ((PMMIO)hmmio)->pchBuffer);
            lDeltaEndRead
                    = (LONG)(((PMMIO)hmmio)->pchEndRead - ((PMMIO)hmmio)->pchBuffer);

            if (cchBuffer >= lDeltaNext)
                break;

            /* caller wants to truncate the part of the buffer
             * that contains <pchNext> -- handle this by
             * emptying the buffer, recalculating <lDeltaNext>
             * and <lDeltaEndRead>, and continuing below
             */
            if ((mmr = mmioFlush(hmmio, MMIO_EMPTYBUF)) != 0)
                return mmr;
        }

        /* reallocate buffer */
	{
	HANDLE hTemp;

        hTemp =  GlobalHandle( ((PMMIO)hmmio)->pchBuffer );

        GlobalUnlock( hTemp );
        hMem = GlobalReAlloc( hTemp
                            , cchBuffer
                            , GMEM_MOVEABLE
                            );
        pch = GlobalLock(hMem);
	dprintf2(("mmioSetBuffer reallocated ptr %8x, handle %8x, to ptr %8x (handle %8x)\n",
		((PMMIO)hmmio)->pchBuffer, hTemp, pch, hMem));

	}

        /* If we cannot allocate the new buffer, exit with no
         *   harm done.
         */
        if (pch == NULL)
            return MMIOERR_OUTOFMEMORY; // out of memory

        /* transfer pointers to new buffer */
        ((PMMIO)hmmio)->cchBuffer = cchBuffer;
        ((PMMIO)hmmio)->pchBuffer = pch;
        ((PMMIO)hmmio)->pchNext = pch + lDeltaNext;
        ((PMMIO)hmmio)->pchEndRead = pch + lDeltaEndRead;

        /* <pchEndWrite> always points to the end of the buf. */
        ((PMMIO)hmmio)->pchEndWrite = ((PMMIO)hmmio)->pchBuffer + cchBuffer;

        /* check if the reallocation truncated valid data */
        if (lDeltaEndRead > cchBuffer)
            ((PMMIO)hmmio)->pchEndRead = ((PMMIO)hmmio)->pchEndWrite;

        return 0;
    }

    /* write the buffer to disk and stop using the buffer */
    if ((mmr = mmioFlush(hmmio, MMIO_EMPTYBUF)) != 0)
        return mmr;

    if (((PMMIO)hmmio)->dwFlags & MMIO_ALLOCBUF)
    {
        hMem = GlobalHandle( ((PMMIO)hmmio)->pchBuffer);
        GlobalUnlock( hMem );
        GlobalFree( hMem );
        ((PMMIO)hmmio)->dwFlags &= ~MMIO_ALLOCBUF;
    }

    /* Initially, no error. */
    mmr = 0;

    if ((pchBuffer == NULL) && (cchBuffer > 0))
    {
        hMem = GlobalAlloc(GMEM_MOVEABLE, cchBuffer);
        if (hMem)
            pchBuffer = GlobalLock(hMem);
        //else pchBuffer = NULL;

        /* If there is an error, change the file to be un-buffered
         * and return an error code.  The file is still valid.
         * (Just for a little extra security.)
         */
        if (pchBuffer == NULL)
        {   mmr = MMIOERR_OUTOFMEMORY;
            cchBuffer = 0L;
        }
        else
          ((PMMIO)hmmio)->dwFlags |= MMIO_ALLOCBUF;
    }

    /* invariant: <pchEndRead> points past the end of the "valid" portion
     * of the buffer, and <pchEndWrite> points past the last byte that
     * can be written into; <pchNext> points to the next byte to read
     * or write; <lBufOffset> is the current disk offset of the start
     * of the buffer, and it will not change
     */
    ((PMMIO)hmmio)->pchBuffer = pchBuffer;
    ((PMMIO)hmmio)->cchBuffer = cchBuffer;
    ((PMMIO)hmmio)->pchNext
                     = ((PMMIO)hmmio)->pchEndRead = ((PMMIO)hmmio)->pchBuffer;
    ((PMMIO)hmmio)->pchEndWrite = ((PMMIO)hmmio)->pchBuffer + cchBuffer;

    return mmr;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    MMRESULT | mmioFlush | This function writes the I/O buffer of a
    file to disk, if the I/O buffer has been written to.

@parm   HMMIO | hmmio | Specifies the file handle of a file opened
    with <f mmioOpen>.

@parm   UINT | uFlags | Is not used and should be set to zero.

@rdesc  The return value is zero if the function is successful.
    Otherwise, the return value specifies an error code. The error
    code can be one of the following codes:

    @flag MMIOERR_CANNOTWRITE | The contents of the buffer could
    not be written to disk.

@comm   Closing a file with <f mmioClose> will automatically flush
    its buffer.

    If there is insufficient disk space to write the
    buffer, <f mmioFlush> will fail, even if the preceding <f mmioWrite>
    calls were successful.
*/
/*--------------------------------------------------------------------*/
MMRESULT APIENTRY
    mmioFlush(HMMIO hmmio, UINT uFlags)
{
    LONG        lBytesAsk;      // no. bytes to write
    LONG        lBytesWritten;      // no. bytes actually written

    V_HANDLE(hmmio, TYPE_MMIO, MMSYSERR_INVALHANDLE);

    if (  ( ((PMMIO)hmmio)->fccIOProc
          == FOURCC_MEM
          )
       || ( ((PMMIO)hmmio)->pchBuffer == NULL )
       )
        return 0;       // cannot flush memory files

    /* if the file is unbuffered then the dirty flag should not be set */
    if (((PMMIO)hmmio)->dwFlags & MMIO_DIRTY)
    {
        /* figure out how many bytes need to be flushed */
        lBytesAsk = (LONG)(((PMMIO)hmmio)->pchEndRead - ((PMMIO)hmmio)->pchBuffer);

        /* write the buffer to disk */
        lBytesWritten = mmioDiskIO(((PMMIO)hmmio), MMIOM_WRITEFLUSH,
            ((PMMIO)hmmio)->pchBuffer, lBytesAsk);
        if (lBytesWritten != lBytesAsk)
            return MMIOERR_CANNOTWRITE;
        ((PMMIO)hmmio)->dwFlags &= ~MMIO_DIRTY; // buffer is clean now
    }

    if (uFlags & MMIO_EMPTYBUF)
    {
        /* empty the I/O buffer, and update <lBufOffset> to reflect
         * what the current file position is
         */
        ((PMMIO)hmmio)->lBufOffset
                    += (LONG)((((PMMIO)hmmio)->pchNext - ((PMMIO)hmmio)->pchBuffer));
        ((PMMIO)hmmio)->pchNext
                    = ((PMMIO)hmmio)->pchEndRead = ((PMMIO)hmmio)->pchBuffer;
    }

    return 0;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    MMRESULT | mmioAdvance | This function advances the I/O buffer of
    a file set up for direct I/O buffer access with <f mmioGetInfo>. If
    the file is opened for reading, the I/O buffer is filled from the
    disk.  If the file is opened for writing and the MMIO_DIRTY flag is
    set in the <e MMIOINFO.dwFlags> field of the <t MMIOINFO> structure,
    the buffer is written to disk.  The <e MMIOINFO.pchNext>,
    <e MMIOINFO.pchEndRead>, and <e MMIOINFO.pchEndWrite> fields of the
    <t MMIOINFO> structure are updated to reflect the new state of
    the I/O buffer.

@parm   HMMIO | hmmio | Specifies the file handle for a file opened
    with <f mmioOpen>.

@parm   LPMMIOINFO | lpmmioinfo | Optionally specifies a pointer to the
    <t MMIOINFO> structure obtained with <f mmioGetInfo>, which is used to
    set the current file information, then updated after the buffer is
    advanced.

@parm   UINT | uFlags | Specifies options for the operation.
    Contains exactly one of the following two flags:

    @flag   MMIO_READ | The buffer is filled from the file.

    @flag   MMIO_WRITE | The buffer is written to the file.

@rdesc  The return value is zero if the operation is successful.
    Otherwise, the return value specifies an error code. The error
    code can be one of the following codes:

    @flag MMIOERR_CANNOTWRITE | The contents of the buffer could
    not be written to disk.

    @flag MMIOERR_CANNOTREAD | An error occurred while re-filling
    the buffer.

    @flag MMIOERR_UNBUFFERED | The specified file is not opened
    for buffered I/O.

    @flag MMIOERR_CANNOTEXPAND | The specified memory file cannot
    be expanded, probably because the <e MMIOINFO.adwInfo[0]> field
    was set to zero in the initial call to <f mmioOpen>.

    @flag MMIOERR_OUTOFMEMORY | There was not enough memory to expand
    a memory file for further writing.


@comm   If the specified file is opened for writing or for both
    reading and writing, the I/O buffer will be flushed to disk before
    the next buffer is read. If the I/O buffer cannot be written to disk
    because the disk is full, then <f mmioAdvance> will return
    MMIOERR_CANNOTWRITE.

    If the specified file is only open for writing, the MMIO_WRITE
    flag must be specified.

    If you have written to the I/O buffer, you must set the MMIO_DIRTY
    flag in the <e MMIOINFO.dwFlags> field of the <t MMIOINFO> structure
    before calling <f mmioAdvance>. Otherwise, the buffer will not be
    written to disk.

    If the end of file is reached, <f mmioAdvance> will still return
    success, even though no more data can be read.  Thus, to check for
    the end of the file, it is necessary to see if the
    <e MMIOINFO.pchNext> and <e MMIOINFO.pchEndRead> fields of the
    <t MMIOINFO> structure are equal after calling <f mmioAdvance>.

@xref   mmioGetInfo MMIOINFO
*/
/*--------------------------------------------------------------------*/
MMRESULT APIENTRY
         mmioAdvance(HMMIO hmmio, LPMMIOINFO lpmmioinfo, UINT uFlags)
{
    LONG        lBytesRead;     // bytes actually read
    UINT        w;

    V_HANDLE(hmmio, TYPE_MMIO, MMSYSERR_INVALHANDLE);
    if (((PMMIO)hmmio)->pchBuffer == NULL)
        return MMIOERR_UNBUFFERED;
    if (lpmmioinfo != NULL) {
        V_WPOINTER(lpmmioinfo, sizeof(MMIOINFO), MMSYSERR_INVALPARAM);
        mmioSetInfo(hmmio, lpmmioinfo, 0);
    }

    if (((PMMIO)hmmio)->fccIOProc == FOURCC_MEM)
    {
        /* this is a memory file:
         *   -- if the caller is reading, cannot advance
         *   -- if the caller is writing, then advance by expanding
         *      the buffer (if possible) if the there is less than
         *  <adwInfo[0]> bytes left in the buffer
         */
        if (!(uFlags & MMIO_WRITE))
            return MMIOERR_CANNOTREAD;
        if ( (DWORD)(((PMMIO)hmmio)->pchEndWrite - ((PMMIO)hmmio)->pchNext)
           >= ((PMMIO)hmmio)->adwInfo[0]
           )
            return MMIOERR_CANNOTEXPAND;
        if ((w = mmioExpandMemFile(((PMMIO)hmmio), 1L)) != 0)
            return w;   // out of memory, or whatever
        goto GETINFO_AND_EXIT;
    }

    /* empty the I/O buffer, which will effectively advance the
     * buffer by (<pchNext> - <pchBuffer>) bytes
     */
    if ((w = mmioFlush(hmmio, MMIO_EMPTYBUF)) != 0)
        return w;

    /* if MMIO_WRITE bit is not set in uFlags, fill the buffer  */
    if (!(uFlags & MMIO_WRITE))
    {
        /* read the next bufferful from the file */
        lBytesRead = mmioDiskIO(((PMMIO)hmmio), MMIOM_READ,
            ((PMMIO)hmmio)->pchBuffer, ((PMMIO)hmmio)->cchBuffer);
        if (lBytesRead == -1)
            return MMIOERR_CANNOTREAD;

        /* reading zero bytes should not be treated as an error
         * condition -- e.g. open a new file R+W and call
         * mmioAdvance(), and MMIOM_READ will return zero bytes
         * because the file started off empty
         */
        ((PMMIO)hmmio)->pchEndRead += lBytesRead;
    }

GETINFO_AND_EXIT:

    /* copy <hmmio> back to <lpmmioinfo> if <lpmmioinfo> is provided */
    if (lpmmioinfo != NULL)
        mmioGetInfo(hmmio, lpmmioinfo, 0);

    return 0;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    FOURCC | mmioStringToFOURCC | This function converts a
    null-terminated string to a four-character code.

@parm   LPCTSTR | sz | Specifies a pointer to a null-terminated
    string to a four-character code.

@parm   UINT | uFlags | Specifies options for the conversion:

    @flag   MMIO_TOUPPER | Converts all characters to uppercase.

@rdesc  The return value is the four character code created from the
    given string.

@comm   This function does not check to see if the string referenced
    by <p sz> follows any conventions regarding which characters to
    include in a four-character code.  The string is
    simply copied to a four-character code and padded with blanks or
    truncated to four characters if required.

@xref   mmioFOURCC
*/
/*--------------------------------------------------------------------*/
FOURCC APIENTRY
       mmioStringToFOURCCW( LPCWSTR sz, UINT uFlags )
{

    FOURCC  fcc;
    PBYTE   pByte;  // ascii version of szFileName
    ULONG   cbDst;  // character count of szFileName

//    V_STRING(sz, -1, 0);

    /*------------------------------------------------------------*\
     * Convert the given unicode string into ascii and then call
     * the ascii version of mmioStringToFOURCCW
    \*------------------------------------------------------------*/
    cbDst = (wcslen( sz ) * sizeof(WCHAR)) + sizeof(WCHAR);
    pByte = HeapAlloc( hHeap, 0, cbDst );
    if ( pByte == (PBYTE)NULL ) {
        return (FOURCC)(DWORD_PTR)NULL;
    }
    UnicodeStrToAsciiStr( pByte, pByte + cbDst, sz );

    fcc = mmioStringToFOURCCA( (LPSTR)pByte, uFlags );

    HeapFree( hHeap, 0, pByte );
    return (FOURCC)fcc;
}

FOURCC APIENTRY
       mmioStringToFOURCCA( LPCSTR sz, UINT uFlags )
{
    FOURCC      fcc;
    LPSTR       pch = (LPSTR) &fcc;
    int         i;

    V_STRING(sz, (DWORD)-1, 0);

    for (i = sizeof(FOURCC) - 1; i >= 0; i--)
    {
        if (!*sz)
            *pch = ' ';   /* and don't increment sz beyond the terminating NULL! */
        else {
            *pch = *sz;
            if (uFlags & MMIO_TOUPPER)

//#ifdef DBCS // we don't allow DBCS string. This is enough for us.
                *pch = (char)(WORD)PtrToUlong(AnsiUpper((LPSTR)(DWORD_PTR)((ULONG)*pch & 0xff)));
//#else
//                *pch = (char)(WORD)(LONG)AnsiUpper((LPSTR)(LONG)*pch);
//#endif

            sz++;
        }
        pch++;
    }

    return fcc;
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    LPMMIOPROC | mmioInstallIOProc | This function installs or
    removes a custom I/O procedure. It will also locate an installed I/O
    procedure, given its corresponding four-character code.

@parm   FOURCC | fccIOProc | Specifies a four-character code
    identifying the I/O procedure to install, remove, or locate. All
    characters in this four-character code should be uppercase characters.

@parm   LPMMIOPROC | pIOProc | Specifies the address of the I/O
    procedure to install. To remove or locate an I/O procedure, set this
    parameter to NULL.

@parm   DWORD | dwFlags | Specifies one of the following flags
    indicating whether the I/O procedure is being installed, removed, or
    located:

    @flag   MMIO_INSTALLPROC | Installs the specified I/O procedure.

    @flag   MMIO_GLOBALPROC | This flag is a modifier to the install flag,
        and indicates the I/O procedure should be installed for global
        use.  This flag is ignored on removal or find.

    @flag   MMIO_REMOVEPROC | Removes the specified I/O procedure.

    @flag   MMIO_FINDPROC | Searches for the specified I/O procedure.

@rdesc  The return value is the address of the I/O procedure
    installed, removed, or located. If there is an error, the return value
    is NULL.

@comm   If the I/O procedure resides in the application, use
    <f MakeProcInstance> for compatibility with 16 bit windows
    to get a procedure-instance address and specify
    this address for <p pIOProc>. You don't need to get a procedure-instance
    address if the I/O procedure resides in a DLL.

@cb LONG FAR PASCAL | IOProc | <f IOProc> is a placeholder for the
    application-supplied function name. The actual name must be exported
    by including it in a EXPORTS statement in the application's
    module-definitions file.

    @parm   LPSTR | lpmmioinfo | Specifies a pointer to an
        <t MMIOINFO> structure containing information about the open
        file.  The I/O procedure must maintain the <e MMIOINFO.lDiskOffset>
        field in this structure to indicate the file offset to the
        next read or write location. The I/O procedure can use the
        <e MMIOINFO.adwInfo[]> field to store state information. The
        I/O procedure should not modify any other fields of the
        <t MMIOINFO> structure.


    @parm   UINT | wMsg | Specifies a message indicating the
        requested I/O operation. Messages that can be received include
        <m MMIOM_OPEN>, <m MMIOM_CLOSE>, <m MMIOM_READ>, <m MMIOM_WRITE>,
        and <m MMIOM_SEEK>.

    @parm   LONG | lParam1 | Specifies a parameter for the message.

    @parm   LONG | lParam2 | Specifies a parameter for the message.

@rdesc  The return value depends on the message specified by
    <p wMsg>. If the I/O procedure does not recognize a message, it should
    return zero.

@comm   The four-character code specified by the
    <e MMIOINFO.fccIOProc> field in the <t MMIOINFO> structure
    associated with a file identifies a filename extension for a custom
    storage system. When an application calls <f mmioOpen> with a
    filename such as "foo.xyz!bar", the I/O procedure associated with the
    four-character code "XYZ " is called to open the "bar" element of the
    file "foo.xyz".

    The <f mmioInstallIOProc> function maintains a separate list of
    installed I/O procedures for each Windows application. Therefore,
    different applications can use the same I/O procedure identifier for
    different I/O procedures without conflict.  Installing an I/O procedure
    globally however enables any process to use the procedure.

    If an application calls <f mmioInstallIOProc> more than once to
    register the same I/O procedure, then it must call
    <f mmioInstallIOProc> to remove the procedure once for each time it
    installed the procedure.

    <f mmioInstallIOProc> will not prevent an application from
    installing two different I/O procedures with the same identifier, or
    installing an I/O procedure with one of the predefined identifiers
    ("DOS ", "MEM "). The most recently installed procedure
    takes precedence, and the most recently installed procedure is the
    first one to get removed.

    When searching for a specified I/O procedure, local procedures are
    searched first, then global procedures.

@xref   mmioOpen
 */

/*--------------------------------------------------------------------*/
LPMMIOPROC APIENTRY
mmioInstallIOProcW(FOURCC fccIOProc, LPMMIOPROC pIOProc, DWORD dwFlags)
{
    V_FLAGS(dwFlags, MMIO_VALIDPROC, mmioInstallIOProc, NULL);

    dwFlags |= MMIO_UNICODEPROC;
    return mmioInternalInstallIOProc( fccIOProc, pIOProc, dwFlags);
}

LPMMIOPROC APIENTRY
mmioInstallIOProcA(FOURCC fccIOProc, LPMMIOPROC pIOProc, DWORD dwFlags)
{

    V_FLAGS(dwFlags, MMIO_VALIDPROC, mmioInstallIOProc, NULL);

    dwFlags &= ~MMIO_UNICODEPROC;
    return mmioInternalInstallIOProc( fccIOProc, pIOProc, dwFlags);
}


static LPMMIOPROC mmioInternalInstallIOProc(
                     FOURCC      fccIOProc,   // I/O Proc 4 char id
                     LPMMIOPROC  pIOProc,     // pointer to any I/O proc to install
                     DWORD       dwFlags      // flags from caller
                     )
{
    IOProcMapEntry  *pEnt;          // an entry in linked list
    HANDLE          hTaskCurrent;   // current Windows task handle

#ifdef DUMPIOPROCLIST
// dprintf(("initial I/O proc list\n"));
// DumpIOProcList();
#endif

    if (fccIOProc == 0L)
        return NULL;

    hTaskCurrent = GetCurrentTask();

    if (dwFlags & MMIO_INSTALLPROC)
    {
        /* install I/O procedure -- always add at the beginning of
         * the list, so it overrides any other I/O procedures
         * with the same identifier installed by the same task
         */
        V_CALLBACK((FARPROC)pIOProc, NULL);
        if ((pEnt = (IOProcMapEntry NEAR *)
            NewHandle(TYPE_MMIO, NULL, sizeof(IOProcMapEntry))) == NULL)
                return NULL;        // out of memory
        //  Implicitly acquired by NewHandle()
        ReleaseHandleListResource();
        pEnt->fccIOProc = fccIOProc;
        pEnt->pIOProc = pIOProc;
        pEnt->hTask = hTaskCurrent;
        pEnt->pNext = gIOProcMapHead;
        gIOProcMapHead = pEnt;

#ifdef DUMPIOPROCLIST
// dprintf(("I/O proc list after addition"));
// DumpIOProcList();
#endif

        return pIOProc;
    }

    if (!pIOProc)
        if (dwFlags & MMIO_REMOVEPROC)
            return RemoveIOProc(fccIOProc, hTaskCurrent);
        else if (dwFlags & MMIO_FINDPROC)
        {   
            pEnt = FindIOProc(fccIOProc, hTaskCurrent);
            return ( pEnt==NULL
                   ? NULL
                   : pEnt->pIOProc
                   );
        }
    return NULL;        // couldn't find requested I/O procedure
}


/*--------------------------------------------------------------------*/
/* @doc EXTERNAL

@api    LRESULT | mmioSendMessage | This function sends a message to the
    I/O procedure associated with the specified file.

@parm   HMMIO | hmmio | Specifies the file handle for a file opened
    with <f mmioOpen>.

@parm   UINT | wMsg | Specifies the message to send to the I/O procedure.

@parm   LONG | lParam1 | Specifies a parameter for the message.

@parm   LONG | lParam2 | Specifies a parameter for the message.

@rdesc  The return value depends on the message. If the I/O procedure
    does not recognize the message, the return value is zero.

@comm   Use this function to send custom user-defined messages. Do
    not use it to send the <m MMIOM_OPEN>, <m MMIOM_CLOSE>,
    <m MMIOM_READ>, <m MMIOM_WRITE>, <m MMIOM_WRITEFLUSH>, or
    <m MMIOM_SEEK> messages. Define
    custom messages to be greater than or equal to the MMIOM_USER constant.

@xref   mmioInstallIOProc
*/
/*--------------------------------------------------------------------*/
LRESULT APIENTRY
mmioSendMessage(HMMIO hmmio, UINT uMsg, LPARAM lParam1, LPARAM lParam2)
{
    V_HANDLE(hmmio, TYPE_MMIO, (LRESULT)0);
    return IOProc( (PMMIO)hmmio, uMsg, lParam1, lParam2);
}


/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@api    LONG | mmioDiskIO | Perform an unbuffered read or write.
    Do not assume where the current disk offset <p lDiskOffset> will be.

@parm   PMMIO | pmmio | The open file handle returned by <f mmioOpen>.

@parm   UINT | wMsg | MMIOM_READ if <f mmioDiskIO> should read from the disk,
    or MMIOM_WRITE if <f mmioDiskIO> should write to the disk,
    or MMIOM_WRITEFLUSH if <f mmioDiskIO> should flush all pending I/O.

@parm   LPSTR | pch | The buffer to read into or write from.

@parm   LONG | cch | The number of bytes to read or write.

    <f mmioDiskIO> changes the disk offset to be <p lBufOffset>
    and then performs an MMIOM_READ or MMIOM_WRITE operation as
    specified by <p wMsg>, <p pch>, and <p cch>.

    Note that if the I/O buffer is not empty at this point, this
    function may not do what you expect.

    Do not call this function for memory files.
*/
/*--------------------------------------------------------------------*/
static LONG NEAR PASCAL
mmioDiskIO(PMMIO pmmio, UINT uMsg, LPSTR pch, LONG cch)
{
    if (pmmio->lDiskOffset != pmmio->lBufOffset)
    {
        if (IOProc( pmmio
                  , MMIOM_SEEK
                  , (LONG) pmmio->lBufOffset
                  , (LONG) SEEK_SET
                  )
           == -1
           )
            return -1;
    }

    return (LONG)IOProc( pmmio, uMsg, (LPARAM) pch, (LPARAM) cch);
}


/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@api    UINT | mmioExpandMemFile | Assuming that <p pmmio> is a memory file,
    expand it by <p lExpand> bytes or <p adwInfo[0]> bytes, whichever
    is larger.  Do not disturb the contents of the buffer or change
    the current file position.

@parm   PMMIO | pmmio | The open file handle returned by <f mmioOpen>.

@parm   LONG | lExpand | The minimum number of bytes to expand the buffer by.

@rdesc  If the function succeeds, zero is returned.  If the function fails,
    an error code is returned.  In particular, MMIOERR_OUTOFMEMORY is
    returned if memory reallocation failed.

@comm   Only call this function for memory files.
*/
/*--------------------------------------------------------------------*/
static UINT NEAR PASCAL
mmioExpandMemFile(PMMIO pmmio, LONG lExpand)
{
    MMIOMEMINFO *   pInfo = (MMIOMEMINFO *) pmmio->adwInfo;
    DWORD       dwFlagsTemp;
    UINT        w;

    /* make sure buffer can be expanded */
    /* Note: we used to check ALLOC_BUF here, we don't now. */
    if (pInfo->lExpand == 0)
        return MMIOERR_CANNOTEXPAND;    // cannot grow file

    /* how much should the buffer be expanded by? */
    if (lExpand < pInfo->lExpand)
        lExpand = pInfo->lExpand;

    dwFlagsTemp = pmmio->dwFlags;
    pmmio->dwFlags |= MMIO_ALLOCBUF;
    w = mmioSetBuffer(((HMMIO)pmmio), NULL,
                     pmmio->cchBuffer + lExpand, 0);
    pmmio->dwFlags = dwFlagsTemp;
    return w;
}


/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@api    LRESULT | mmioDOSIOProc | The 'DOS' I/O procedure, which handles I/O
    on ordinary DOS files.

@parm   LPSTR | lpmmioinfo | A pointer to an MMIOINFO block that
    contains information about the open file.

@parm   UINT | uMsg | The message that the I/O procedure is being
    asked to execute.

@parm   LONG | lParam1 | Specifies additional message information.

@parm   LONG | lParam2 | Specifies additional message information.

@rdesc  Return value depends on <p wMsg>.
*/
/*--------------------------------------------------------------------*/
LRESULT
     mmioDOSIOProc(LPSTR lpmmioStr, UINT uMsg, LPARAM lParam1, LPARAM lParam2)
{
    PMMIO       pmmio  = (PMMIO)lpmmioStr;              // only in DLL!
    MMIODOSINFO *pInfo = (MMIODOSINFO *)pmmio->adwInfo;
    LONG        lResult;
    LPWSTR      szFilePart;
    WCHAR       szPath[ MAX_PATH ];

    switch (uMsg) {

    case MMIOM_OPEN:
        /*
         * The extra info parameter optionally contains a
         * sequence number to pass.
         */
        if ( pmmio->dwFlags & MMIO_GETTEMP )
        {
            V_RPOINTER((LPSTR)lParam1, 4, (LRESULT) MMSYSERR_INVALPARAM);

            if ( GetTempPathW( MAX_PATH, szPath ) == 0 ) {
                wcscpy( szPath, (LPCWSTR)L"." );
            }

            return GetTempFileNameW( szPath, (LPCWSTR)L"sje",
                                    (WORD)pmmio->adwInfo[0], (LPWSTR)lParam1 )
                   ? (LRESULT)0
                   : (LRESULT)MMIOERR_FILENOTFOUND;
        }


        /*------------------------------------------------------------*\
         * <lParam1> is either a file name or NULL; if it is
         * NULL, then <adwInfo[0]>, which is actually <pInfo->fh>,
         * should already contain an open DOS file handle.
         *
         * Does lParam1 point to a file name ?
         *
         * if so then either:
         *
         *  delete the file,
         *  check the existance of the file,
         *  parse the file name, or
         *  open the file name
         *
        \*------------------------------------------------------------*/
        if ( lParam1 != 0 ) {

            if ( pmmio->dwFlags & MMIO_DELETE ) {

                return DeleteFileW( (LPWSTR)lParam1 )
                       ? (LRESULT)0
                       : (LRESULT)MMIOERR_FILENOTFOUND;
            }

            if ( pmmio->dwFlags & MMIO_EXIST ) {
                if ( !(pmmio->dwFlags & MMIO_CREATE) ) {
#ifdef LATER
      I think this should be using SearchPath (with lpszPath==lParam1)
      as the definition of MMIO_EXIST states that a fully qualified
      filename is returned.  OR tweak the flags to turn MMIO_PARSE ON
      and execute the next section.
#endif
                    if ( GetFileAttributesW( (LPWSTR)lParam1 ) == -1 ) {
                        return (LRESULT)MMIOERR_FILENOTFOUND;
                    }
                    return (LRESULT)0;
                }
            }

            if ( pmmio->dwFlags & MMIO_PARSE ) {

                if ( GetFullPathNameW((LPWSTR)lParam1,
                                  MAX_PATH,
                                  szPath,
                                  &szFilePart ) == 0 ) {

                    return (LRESULT)MMIOERR_FILENOTFOUND;
                }
                wcscpy( (LPWSTR)lParam1, szPath );
                return (LRESULT) 0;
            }

            {
                DWORD   dwAccess        = 0;
                DWORD   dwSharedMode    = 0;
                DWORD   dwCreate        = 0;
                DWORD   dwFlags         = FILE_ATTRIBUTE_NORMAL;

                /*----------------------------------------------------*\
                 * Look at the access flags
                \*----------------------------------------------------*/
                if ( pmmio->dwFlags & MMIO_WRITE ) {
                    dwAccess = GENERIC_WRITE;
                } else {
                    dwAccess = GENERIC_READ;
                }

                if ( pmmio->dwFlags & MMIO_READWRITE ) {
                    dwAccess |= (GENERIC_WRITE | GENERIC_READ);
                }

                /*----------------------------------------------------*\
                 * Set dwSharedMode from the share flags
                \*----------------------------------------------------*/

                {   /* owing to some crappy design in WIN3.1, the share flags are
                    *  exclusive  = 10
                    *  deny write = 20
                    *  deny read  = 30
                    *  deny none  = 40
                    *  so deny read looks like exclusive + deny write.  Sigh.
                    *  00 is taken as being DENYNONE (probably correct)
                    *  So is 50, 60 and 70 (which is probably bogus).
                    *  As we need to support the DOS flags for WOW, we need this
                    *  code somewhere, so might as well leave the flag definitions
                    *  as they are.  First pull out all the share mode bits.
                    */
                    DWORD dwShare = MMIO_DENYWRITE | MMIO_DENYREAD
                                  | MMIO_DENYNONE | MMIO_EXCLUSIVE;
                    dwShare &= pmmio->dwFlags;

                    switch (dwShare)
                    {   case MMIO_DENYWRITE:
                           dwSharedMode = FILE_SHARE_READ;
                        break;
                        case MMIO_DENYREAD:
                           dwSharedMode = FILE_SHARE_WRITE;
                        break;
                        case MMIO_EXCLUSIVE:
                           dwSharedMode = 0;
                        break;
                        case MMIO_DENYNONE:
                        default:
                           dwSharedMode = FILE_SHARE_WRITE | FILE_SHARE_READ;
                        break;
#ifdef later
   Generate an error for invalid flags?
#endif
                    }
                }

                /*----------------------------------------------------*\
                 * Look at the create flags
                \*----------------------------------------------------*/
                if ( (pmmio->dwFlags) & MMIO_CREATE) {
                    UINT    cch  = sizeof(szPath)/sizeof(szPath[0]);
                    LPWSTR  pstr = (LPWSTR)lParam1;
                
                    dwCreate = CREATE_ALWAYS;
                    
                    lstrcpynW( szPath, pstr, cch );
                    szPath[cch-1] = TEXT('\0');
                    if (lstrlenW(pstr) > lstrlenW(szPath))
                    {
                        //  Filename was truncated.
                        return (LRESULT)MMIOERR_INVALIDFILE;
                    }
                } else {
                    dwCreate = OPEN_EXISTING;
                    if ( SearchPathW( NULL, (LPWSTR)lParam1,
                                      NULL,
                                      (MAX_PATH - 1),
                                      szPath, &szFilePart ) == 0 ) {

                        return (LRESULT)MMIOERR_FILENOTFOUND;
                    }
                }

                pInfo->fh = (int)(DWORD_PTR)CreateFileW( szPath,
                                              dwAccess,
                                              dwSharedMode,
                                              NULL,
                                              dwCreate,
                                              dwFlags | FILE_FLAG_SEQUENTIAL_SCAN,
                                              NULL );

                if ( pInfo->fh == (int)-1 ) {
                    return (LRESULT)MMIOERR_FILENOTFOUND;
                }

                if ( pmmio->dwFlags & MMIO_EXIST ) {
                    CloseHandle( (HANDLE)(UINT_PTR)pInfo->fh );
                    return (LRESULT)0;
                }

            }

        }
        /* check the current file offset */
        pmmio->lDiskOffset = _llseek(pInfo->fh, 0L, SEEK_CUR);
        return (LRESULT)0;

    case MMIOM_CLOSE:
        /* MMIO_FHOPEN flag means keep the DOS file handle open */
        if (  !((DWORD)lParam1 & MMIO_FHOPEN)
           && (_lclose(pInfo->fh) == HFILE_ERROR) ) {

            return (LRESULT) MMIOERR_CANNOTCLOSE;
        }
        return (LRESULT) 0;

    case MMIOM_READ:
        lResult = _lread(pInfo->fh, (LPVOID)lParam1, (LONG)lParam2);
        if (lResult != -1L) {
            pmmio->lDiskOffset += lResult;
        }
        return (LRESULT) lResult;

    case MMIOM_WRITE:
    case MMIOM_WRITEFLUSH:

        lResult = _lwrite(pInfo->fh, (LPVOID)lParam1, (LONG)lParam2);
        if (lResult != -1L) {
            pmmio->lDiskOffset += lResult;
        }

#ifdef DOSCANFLUSH
        if (uMsg == MMIOM_WRITEFLUSH)
        {
            /* Issue hardware flush command */
        }
#endif
        return (LRESULT) lResult;

    case MMIOM_SEEK:
        lResult = _llseek(pInfo->fh, (LONG)lParam1, (int)(LONG)lParam2);
        if (lResult != -1L) {
            pmmio->lDiskOffset = lResult;
        }
        return (LRESULT) lResult;

    case MMIOM_RENAME:
        if (!MoveFileW((LPWSTR)lParam1, (LPWSTR)lParam2)) {
            return (LRESULT) MMIOERR_FILENOTFOUND;
            /* ??? There are other errors too? e.g. target exists? */
        }
        break;

    }

    return (LRESULT) 0;
}


/*--------------------------------------------------------------------*/
/* @doc INTERNAL

@api    LRESULT | mmioMEMIOProc | The 'MEM' I/O procedure, which handles I/O
    on memory files.

@parm   LPSTR | lpmmioinfo | A pointer to an MMIOINFO block that
    contains information about the open file.

@parm   UINT | uMsg | The message that the I/O procedure is being
    asked to execute.

@parm   LONG | lParam1 | Specifies additional message information.

@parm   LONG | lParam2 | Specifies additional message information.

@rdesc  Return value depends on <p uMsg>.
*/
/*--------------------------------------------------------------------*/
LRESULT
      mmioMEMIOProc(LPSTR lpmmioStr, UINT uMsg, LPARAM lParam1, LPARAM lParam2)
{
    PMMIO       pmmio = (PMMIO) lpmmioStr; // only in DLL!

    switch (uMsg)
    {

        case MMIOM_OPEN:

        if ( pmmio->dwFlags
           & ~(MMIO_CREATE
              | MMIO_READWRITE
              | MMIO_WRITE
              | MMIO_EXCLUSIVE
              | MMIO_DENYWRITE
              | MMIO_DENYREAD
              | MMIO_DENYNONE
              | MMIO_ALLOCBUF
              )
           )
            return (LRESULT) MMSYSERR_INVALFLAG;

        /* all the data in the buffer is valid */
        if (!(pmmio->dwFlags & MMIO_CREATE))
            pmmio->pchEndRead = pmmio->pchEndWrite;
        return (LRESULT) 0;

    case MMIOM_CLOSE:

        /* nothing special to do on close */
        return (LRESULT) 0;

    case MMIOM_READ:
    case MMIOM_WRITE:
    case MMIOM_WRITEFLUSH:
    case MMIOM_SEEK:
                return (LRESULT) -1;
    }

    return (LRESULT) 0;
}