gdal-3.3.3/gcore/gdalvirtualmem.cpp

/**********************************************************************
 *
 * Name:     gdalvirtualmem.cpp
 * Project:  GDAL
 * Purpose:  Dataset and rasterband exposed as a virtual memory mapping.
 * Author:   Even Rouault, <even dot rouault at spatialys.com>
 *
 **********************************************************************
 * Copyright (c) 2014, Even Rouault <even dot rouault at spatialys.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ****************************************************************************/

#include "cpl_port.h"
#include "gdal.h"
#include "gdal_priv.h"

#include <cstddef>
#include <cstring>

#include <algorithm>

#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_virtualmem.h"

// To be changed if we go to 64-bit RasterIO coordinates and spacing.
using coord_type = int;
using spacing_type = int;

/************************************************************************/
/*                            GDALVirtualMem                            */
/************************************************************************/

class GDALVirtualMem
{
    GDALDatasetH hDS = nullptr;
    GDALRasterBandH hBand = nullptr;
    coord_type nXOff = 0;
    coord_type nYOff = 0;
    // int nXSize;
    // int nYSize;
    coord_type nBufXSize = 0;
    coord_type nBufYSize = 0;
    GDALDataType eBufType = GDT_Byte;
    int nBandCount = 0;
    int* panBandMap = nullptr;
    int nPixelSpace = 0;
    GIntBig nLineSpace = 0;
    GIntBig nBandSpace = 0;

    bool bIsCompact = false;
    bool bIsBandSequential = false;

    bool IsCompact() const { return bIsCompact; }
    bool IsBandSequential() const { return bIsBandSequential; }

    void GetXYBand( size_t nOffset, coord_type& x, coord_type& y,
                    int& band ) const;
    size_t GetOffset( const coord_type& x, const coord_type& y, int band ) const;
    bool GotoNextPixel( coord_type& x, coord_type& y, int& band ) const;

    void DoIOBandSequential( GDALRWFlag eRWFlag, size_t nOffset,
                             void* pPage, size_t nBytes ) const;
    void DoIOPixelInterleaved( GDALRWFlag eRWFlag, size_t nOffset,
                               void* pPage, size_t nBytes ) const;

    CPL_DISALLOW_COPY_ASSIGN(GDALVirtualMem)

public:
             GDALVirtualMem( GDALDatasetH hDS,
                             GDALRasterBandH hBand,
                             const coord_type& nXOff,
                             const coord_type& nYOff,
                             const coord_type& nXSize,
                             const coord_type& nYSize,
                             const coord_type& nBufXSize,
                             const coord_type& nBufYSize,
                             GDALDataType eBufType,
                             int nBandCount, const int* panBandMapIn,
                             int nPixelSpace,
                             GIntBig nLineSpace,
                             GIntBig nBandSpace );
            ~GDALVirtualMem();

    static void FillCacheBandSequential( CPLVirtualMem* ctxt,  size_t nOffset,
                                         void* pPageToFill,
                                         size_t nToFill, void* pUserData );
    static void SaveFromCacheBandSequential( CPLVirtualMem* ctxt,
                                             size_t nOffset,
                                             const void* pPageToBeEvicted,
                                             size_t nToEvicted,
                                             void* pUserData );

    static void FillCachePixelInterleaved( CPLVirtualMem* ctxt, size_t nOffset,
                                           void* pPageToFill,
                                           size_t nToFill, void* pUserData );
    static void SaveFromCachePixelInterleaved( CPLVirtualMem* ctxt,
                                               size_t nOffset,
                                               const void* pPageToBeEvicted,
                                               size_t nToEvicted,
                                               void* pUserData);

    static void Destroy(void* pUserData);
};

/************************************************************************/
/*                             GDALVirtualMem()                         */
/************************************************************************/

GDALVirtualMem::GDALVirtualMem( GDALDatasetH hDSIn,
                                GDALRasterBandH hBandIn,
                                const coord_type& nXOffIn,
                                const coord_type& nYOffIn,
                                const coord_type& /* nXSize */,
                                const coord_type& /* nYSize */,
                                const coord_type& nBufXSizeIn,
                                const coord_type& nBufYSizeIn,
                                GDALDataType eBufTypeIn,
                                int nBandCountIn, const int* panBandMapIn,
                                int nPixelSpaceIn,
                                GIntBig nLineSpaceIn,
                                GIntBig nBandSpaceIn ) :
    hDS(hDSIn),
    hBand(hBandIn),
    nXOff(nXOffIn),
    nYOff(nYOffIn),
    // TODO(schwehr): Why not used or removed?
    // nXSize(nXSize),
    // nYSize(nYSize),
    nBufXSize(nBufXSizeIn),
    nBufYSize(nBufYSizeIn),
    eBufType(eBufTypeIn),
    nBandCount(nBandCountIn),
    nPixelSpace(nPixelSpaceIn),
    nLineSpace(nLineSpaceIn),
    nBandSpace(nBandSpaceIn)
{
    if( hDS != nullptr )
    {
        panBandMap = static_cast<int *>( CPLMalloc(nBandCount * sizeof(int)) );
        if( panBandMapIn )
        {
            memcpy(panBandMap, panBandMapIn, nBandCount * sizeof(int));
        }
        else
        {
            for( int i = 0; i < nBandCount; i++ )
                panBandMap[i] = i + 1;
        }
    }
    else
    {
        panBandMap = nullptr;
        nBandCount = 1;
    }

    const int nDataTypeSize = GDALGetDataTypeSizeBytes(eBufType);
    if( nPixelSpace == nDataTypeSize &&
        nLineSpace == static_cast<GIntBig>(nBufXSize) * nPixelSpace &&
        nBandSpace == nBufYSize * nLineSpace )
        bIsCompact = true;
    else if( nBandSpace == nDataTypeSize &&
             nPixelSpace == nBandCount * nBandSpace &&
             nLineSpace == static_cast<GIntBig>(nBufXSize) * nPixelSpace )
        bIsCompact = true;
    else
        bIsCompact = false;

    bIsBandSequential = nBandSpace >= nBufYSize * nLineSpace;
}

/************************************************************************/
/*                            ~GDALVirtualMem()                         */
/************************************************************************/

GDALVirtualMem::~GDALVirtualMem()
{
    CPLFree(panBandMap);
}

/************************************************************************/
/*                              GetXYBand()                             */
/************************************************************************/

void GDALVirtualMem::GetXYBand( size_t nOffset, coord_type& x, coord_type& y,
                                int& band ) const
{
    if( IsBandSequential() )
    {
        if( nBandCount == 1 )
            band = 0;
        else
            band = static_cast<int>(nOffset / nBandSpace);
        y = static_cast<coord_type>((nOffset - band * nBandSpace) / nLineSpace);
        x = static_cast<coord_type>(
            (nOffset - band * nBandSpace - y * nLineSpace) / nPixelSpace );
    }
    else
    {
        y = static_cast<coord_type>(nOffset / nLineSpace);
        x = static_cast<coord_type>((nOffset - y * nLineSpace) / nPixelSpace);
        if( nBandCount == 1 )
            band = 0;
        else
            band = static_cast<int>(
                (nOffset - y * nLineSpace - x * nPixelSpace) / nBandSpace);
    }
}

/************************************************************************/
/*                            GotoNextPixel()                           */
/************************************************************************/

bool GDALVirtualMem::GotoNextPixel( coord_type& x, coord_type& y,
                                    int& band ) const
{
    if( IsBandSequential() )
    {
        ++x;
        if( x == nBufXSize )
        {
            x = 0;
            ++y;
        }
        if( y == nBufYSize )
        {
            y = 0;
            band ++;
            if( band == nBandCount )
                return false;
        }
    }
    else
    {
        band ++;
        if( band == nBandCount )
        {
            band = 0;
            ++x;
        }
        if( x == nBufXSize )
        {
            x = 0;
            ++y;
            if( y == nBufYSize )
                return false;
        }
    }
    return true;
}

/************************************************************************/
/*                              GetOffset()                             */
/************************************************************************/

size_t GDALVirtualMem::GetOffset(const coord_type& x,
                                 const coord_type& y, int band) const
{
    return static_cast<size_t>(
        x * nPixelSpace + y * nLineSpace + band * nBandSpace);
}

/************************************************************************/
/*                          DoIOPixelInterleaved()                      */
/************************************************************************/

void GDALVirtualMem::DoIOPixelInterleaved(
    GDALRWFlag eRWFlag, const size_t nOffset, void* pPage, size_t nBytes ) const
{
    coord_type x = 0;
    coord_type y = 0;
    int band = 0;

    GetXYBand(nOffset, x, y, band);
#ifdef DEBUG_VERBOSE
    fprintf(stderr, "eRWFlag=%d, nOffset=%d, x=%d, y=%d, band=%d\n",/*ok*/
            eRWFlag, static_cast<int>(nOffset), x, y, band);
#endif

    if( eRWFlag == GF_Read && !IsCompact() )
        memset(pPage, 0, nBytes);

    if( band >= nBandCount )
    {
        band = nBandCount - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
    }
    else if( x >= nBufXSize )
    {
        x = nBufXSize - 1;
        band = nBandCount - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
    }

    size_t nOffsetRecompute = GetOffset(x, y, band);
    CPLAssert(nOffsetRecompute >= nOffset);
    size_t nOffsetShift = nOffsetRecompute - nOffset;
    if( nOffsetShift >= nBytes )
        return;

    // If we don't start at the first band for that given pixel, load/store
    // the remaining bands
    if( band > 0 )
    {
        size_t nEndOffsetEndOfPixel = GetOffset(x, y, nBandCount);
        int bandEnd = nBandCount;
        // Check that we have enough space to load/store until last band
        // Should be always OK unless the number of bands is really huge
        if( nEndOffsetEndOfPixel - nOffset > nBytes )
        {
            // Not enough space: find last possible band
            coord_type xEnd, yEnd;
            GetXYBand(nOffset + nBytes, xEnd, yEnd, bandEnd);
            CPLAssert(x == xEnd);
            CPLAssert(y == yEnd);
        }

        // Finish reading/writing the remaining bands for that pixel
        CPL_IGNORE_RET_VAL(GDALDatasetRasterIO(
            hDS, eRWFlag,
            nXOff + x, nYOff + y, 1, 1,
            static_cast<char *>(pPage) + nOffsetShift,
            1, 1, eBufType,
            bandEnd - band, panBandMap + band,
            nPixelSpace,
            static_cast<spacing_type>(nLineSpace),
            static_cast<spacing_type>(nBandSpace) ));

        if( bandEnd < nBandCount )
            return;

        band = nBandCount - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
        nOffsetRecompute = GetOffset(x, y, 0);
        nOffsetShift = nOffsetRecompute - nOffset;
        if( nOffsetShift >= nBytes )
            return;
    }

    // Is there enough place to store/load up to the end of current line ?
    size_t nEndOffsetEndOfLine = GetOffset(nBufXSize-1, y, nBandCount);
    if( nEndOffsetEndOfLine - nOffset > nBytes )
    {
        // No : read/write as many pixels on this line as possible
        coord_type xEnd, yEnd;
        int bandEnd;
        GetXYBand(nOffset + nBytes, xEnd, yEnd, bandEnd);
        CPLAssert(y == yEnd);

        if( x < xEnd )
        {
            CPL_IGNORE_RET_VAL(GDALDatasetRasterIO(
                hDS, eRWFlag,
                nXOff + x, nYOff + y, xEnd - x, 1,
                static_cast<char *>(pPage) + nOffsetShift,
                xEnd - x, 1, eBufType,
                nBandCount, panBandMap,
                nPixelSpace,
                static_cast<spacing_type>(nLineSpace),
                static_cast<spacing_type>(nBandSpace) ));
        }

        // Are there partial bands to read/write for the last pixel ?
        if( bandEnd > 0 )
        {
            x = xEnd;
            nOffsetRecompute = GetOffset(x, y, 0);
            nOffsetShift = nOffsetRecompute - nOffset;
            if( nOffsetShift >= nBytes )
                return;

            if( bandEnd >= nBandCount )
                bandEnd = nBandCount;

            CPL_IGNORE_RET_VAL(GDALDatasetRasterIO(
                hDS, eRWFlag,
                nXOff + x, nYOff + y, 1, 1,
                static_cast<char *>(pPage) + nOffsetShift,
                1, 1, eBufType,
                bandEnd, panBandMap,
                nPixelSpace,
                static_cast<spacing_type>(nLineSpace),
                static_cast<spacing_type>(nBandSpace) ));
        }

        return;
    }

    // Yes, enough place to read/write until end of line
    if( x > 0 || nBytes - nOffsetShift < static_cast<size_t>(nLineSpace) )
    {
        CPL_IGNORE_RET_VAL(GDALDatasetRasterIO(
            hDS, eRWFlag,
            nXOff + x, nYOff + y, nBufXSize - x, 1,
            static_cast<char *>(pPage) + nOffsetShift,
            nBufXSize - x, 1, eBufType,
            nBandCount, panBandMap,
            nPixelSpace,
            static_cast<spacing_type>(nLineSpace),
            static_cast<spacing_type>(nBandSpace) ) );

        // Go to beginning of next line
        x = nBufXSize - 1;
        band = nBandCount - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
        nOffsetRecompute = GetOffset(x, y, 0);
        nOffsetShift = nOffsetRecompute - nOffset;
        if( nOffsetShift >= nBytes )
            return;
    }

    // How many whole lines can we store/load ?
    coord_type nLineCount = static_cast<coord_type>((nBytes - nOffsetShift) / nLineSpace);
    if( y + nLineCount > nBufYSize )
        nLineCount = nBufYSize - y;
    if( nLineCount > 0 )
    {
        CPL_IGNORE_RET_VAL(GDALDatasetRasterIO(
            hDS, eRWFlag,
            nXOff + 0, nYOff + y, nBufXSize, nLineCount,
            static_cast<GByte *>(pPage) + nOffsetShift,
            nBufXSize, nLineCount, eBufType,
            nBandCount, panBandMap,
            nPixelSpace,
            static_cast<spacing_type>(nLineSpace),
            static_cast<spacing_type>(nBandSpace) ) );

        y += nLineCount;
        if( y == nBufYSize )
            return;
        nOffsetRecompute = GetOffset(x, y, 0);
        nOffsetShift = nOffsetRecompute - nOffset;
    }

    if( nOffsetShift < nBytes )
    {
        DoIOPixelInterleaved(
            eRWFlag, nOffsetRecompute,
            static_cast<char*>(pPage) + nOffsetShift,
            nBytes - nOffsetShift );
    }
}

/************************************************************************/
/*                          DoIOPixelInterleaved()                      */
/************************************************************************/

void GDALVirtualMem::DoIOBandSequential(
    GDALRWFlag eRWFlag, const size_t nOffset, void* pPage, size_t nBytes ) const
{
    coord_type x = 0;
    coord_type y = 0;

    int band = 0;
    GetXYBand(nOffset, x, y, band);
#if DEBUG_VERBOSE
    fprintf( stderr, "eRWFlag=%d, nOffset=%d, x=%d, y=%d, band=%d\n",/*ok*/
             eRWFlag, static_cast<int>(nOffset), x, y, band );
#endif

    if( eRWFlag == GF_Read && !IsCompact() )
        memset(pPage, 0, nBytes);

    if( x >= nBufXSize )
    {
        x = nBufXSize - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
    }
    else if( y >= nBufYSize )
    {
        x = nBufXSize - 1;
        y = nBufYSize - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
    }

    size_t nOffsetRecompute = GetOffset(x, y, band);
    CPLAssert(nOffsetRecompute >= nOffset);
    size_t nOffsetShift = nOffsetRecompute - nOffset;
    if( nOffsetShift >= nBytes )
        return;

    // Is there enough place to store/load up to the end of current line?
    size_t nEndOffsetEndOfLine = GetOffset(nBufXSize, y, band);
    if( nEndOffsetEndOfLine - nOffset > nBytes )
    {
        // No : read/write as many pixels on this line as possible
        coord_type xEnd, yEnd;
        int bandEnd;
        GetXYBand(nOffset + nBytes, xEnd, yEnd, bandEnd);
        CPLAssert(y == yEnd);
        CPLAssert(band == bandEnd);
        CPL_IGNORE_RET_VAL(GDALRasterIO(
            hBand ? hBand : GDALGetRasterBand(hDS, panBandMap[band]),
            eRWFlag,
            nXOff + x, nYOff + y, xEnd - x, 1,
            static_cast<char *>(pPage) + nOffsetShift,
            xEnd - x, 1, eBufType,
            nPixelSpace, static_cast<spacing_type>(nLineSpace) ));

        return;
    }

    // Yes, enough place to read/write until end of line
    if( x > 0 || nBytes - nOffsetShift < static_cast<size_t>(nLineSpace) )
    {
        CPL_IGNORE_RET_VAL(GDALRasterIO(
            hBand ? hBand : GDALGetRasterBand(hDS, panBandMap[band]),
            eRWFlag,
                    nXOff + x, nYOff + y, nBufXSize - x, 1,
                    static_cast<char *>(pPage) + nOffsetShift,
                    nBufXSize - x, 1, eBufType,
                    nPixelSpace, static_cast<spacing_type>(nLineSpace) ));

        // Go to beginning of next line
        x = nBufXSize - 1;
        if( !GotoNextPixel(x, y, band) )
            return;
        nOffsetRecompute = GetOffset(x, y, band);
        nOffsetShift = nOffsetRecompute - nOffset;
        if( nOffsetShift >= nBytes )
            return;
    }

    // How many whole lines can we store/load ?
    coord_type nLineCount = static_cast<coord_type>((nBytes - nOffsetShift) / nLineSpace);
    if( y + nLineCount > nBufYSize )
        nLineCount = nBufYSize - y;
    if( nLineCount > 0 )
    {
        CPL_IGNORE_RET_VAL(GDALRasterIO(
            hBand ? hBand : GDALGetRasterBand(hDS, panBandMap[band]),
            eRWFlag,
            nXOff + 0, nYOff + y, nBufXSize, nLineCount,
            static_cast<GByte *>(pPage) + nOffsetShift,
            nBufXSize, nLineCount, eBufType,
            nPixelSpace,
            static_cast<spacing_type>(nLineSpace) ) );

        y += nLineCount;
        if( y == nBufYSize )
        {
            y = 0;
            band ++;
            if( band == nBandCount )
                return;
        }
        nOffsetRecompute = GetOffset(x, y, band);
        nOffsetShift = nOffsetRecompute - nOffset;
    }

    if( nOffsetShift < nBytes )
    {
        DoIOBandSequential( eRWFlag, nOffsetRecompute,
               static_cast<char*>(pPage) + nOffsetShift, nBytes - nOffsetShift );
    }
}

/************************************************************************/
/*                    FillCacheBandSequential()                        */
/************************************************************************/

void GDALVirtualMem::FillCacheBandSequential(
    CPLVirtualMem*,
    size_t nOffset,
    void* pPageToFill,
    size_t nToFill,
    void* pUserData )
{
    const GDALVirtualMem* psParams = static_cast<GDALVirtualMem *>(pUserData);
    psParams->DoIOBandSequential(GF_Read, nOffset, pPageToFill, nToFill);
}

/************************************************************************/
/*                    SaveFromCacheBandSequential()                    */
/************************************************************************/

void GDALVirtualMem::SaveFromCacheBandSequential(
    CPLVirtualMem*,
    size_t nOffset,
    const void* pPageToBeEvicted,
    size_t nToEvicted,
    void* pUserData )
{
    const GDALVirtualMem* psParams = static_cast<GDALVirtualMem *>(pUserData);
    psParams->DoIOBandSequential(
        GF_Write, nOffset, const_cast<void *>(pPageToBeEvicted), nToEvicted);
}

/************************************************************************/
/*                     FillCachePixelInterleaved()                      */
/************************************************************************/

void GDALVirtualMem::FillCachePixelInterleaved(
    CPLVirtualMem*,
    size_t nOffset,
    void* pPageToFill,
    size_t nToFill,
    void* pUserData )
{
    const GDALVirtualMem* psParams = static_cast<GDALVirtualMem *>(pUserData);
    psParams->DoIOPixelInterleaved(GF_Read, nOffset, pPageToFill, nToFill);
}

/************************************************************************/
/*                     SaveFromCachePixelInterleaved()                  */
/************************************************************************/

void GDALVirtualMem::SaveFromCachePixelInterleaved(
    CPLVirtualMem*,
    size_t nOffset,
    const void* pPageToBeEvicted,
    size_t nToEvicted,
    void* pUserData )
{
    const GDALVirtualMem* psParams = static_cast<GDALVirtualMem *>(pUserData);
    psParams->DoIOPixelInterleaved(
        GF_Write, nOffset, const_cast<void *>(pPageToBeEvicted), nToEvicted);
}

/************************************************************************/
/*                                Destroy()                             */
/************************************************************************/

void GDALVirtualMem::Destroy(void* pUserData)
{
    GDALVirtualMem* psParams = static_cast<GDALVirtualMem *>( pUserData );
    delete psParams;
}

/************************************************************************/
/*                      GDALCheckBandParameters()                       */
/************************************************************************/

static bool GDALCheckBandParameters( GDALDatasetH hDS,
                                     int nBandCount, int* panBandMap )
{
    if( nBandCount == 0 )
    {
        CPLError( CE_Failure, CPLE_AppDefined, "nBandCount == 0" );
        return false;
    }

    if( panBandMap != nullptr )
    {
        for( int i = 0; i < nBandCount; i++ )
        {
            if( panBandMap[i] < 1 || panBandMap[i] > GDALGetRasterCount(hDS) )
            {
                CPLError( CE_Failure, CPLE_AppDefined, "panBandMap[%d]=%d",
                          i, panBandMap[i] );
                return false;
            }
        }
    }
    else if( nBandCount > GDALGetRasterCount(hDS) )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                 "nBandCount > GDALGetRasterCount(hDS)" );
        return false;
    }
    return true;
}

/************************************************************************/
/*                          GDALGetVirtualMem()                         */
/************************************************************************/

static CPLVirtualMem* GDALGetVirtualMem( GDALDatasetH hDS,
                                         GDALRasterBandH hBand,
                                         GDALRWFlag eRWFlag,
                                         coord_type nXOff, coord_type nYOff,
                                         coord_type nXSize, coord_type nYSize,
                                         coord_type nBufXSize,
                                         coord_type nBufYSize,
                                         GDALDataType eBufType,
                                         int nBandCount, int* panBandMap,
                                         int nPixelSpace,
                                         GIntBig nLineSpace,
                                         GIntBig nBandSpace,
                                         size_t nCacheSize,
                                         size_t nPageSizeHint,
                                         int bSingleThreadUsage,
                                         CSLConstList /*papszOptions*/ )
{
    CPLVirtualMem* view = nullptr;
    GDALVirtualMem* psParams = nullptr;
    GUIntBig nReqMem = 0;

    if( nXSize != nBufXSize || nYSize != nBufYSize )
    {
        CPLError( CE_Failure, CPLE_NotSupported,
                  "nXSize != nBufXSize || nYSize != nBufYSize" );
        return nullptr;
    }

    int nRasterXSize =
        hDS ? GDALGetRasterXSize(hDS) : GDALGetRasterBandXSize(hBand);
    int nRasterYSize =
        hDS ? GDALGetRasterYSize(hDS) : GDALGetRasterBandYSize(hBand);

    if( nXOff < 0 || nYOff < 0 ||
        nXSize == 0 || nYSize == 0 ||
        nBufXSize < 0 || nBufYSize < 0 ||
        nXOff + nXSize > nRasterXSize ||
        nYOff + nYSize > nRasterYSize )
    {
        CPLError( CE_Failure, CPLE_AppDefined, "Invalid window request" );
        return nullptr;
    }

    if( nPixelSpace < 0 || nLineSpace < 0 || nBandSpace < 0)
    {
        CPLError( CE_Failure, CPLE_NotSupported,
                  "nPixelSpace < 0 || nLineSpace < 0 || nBandSpace < 0" );
        return nullptr;
    }

    if( hDS != nullptr && !GDALCheckBandParameters(hDS, nBandCount, panBandMap ) )
        return nullptr;

    const int nDataTypeSize = GDALGetDataTypeSizeBytes(eBufType);
    if( nPixelSpace == 0 )
        nPixelSpace = nDataTypeSize;
    if( nLineSpace == 0 )
        nLineSpace = static_cast<GIntBig>(nBufXSize) * nPixelSpace;
    if( nBandSpace == 0 )
        nBandSpace = static_cast<GIntBig>(nBufYSize) * nLineSpace;

    // OFFSET = offset(x,y,band) = x * nPixelSpace + y * nLineSpace + band *
    // nBandSpace where 0 <= x < nBufXSize and 0 <= y < nBufYSize and 0 <= band
    // < nBandCount if nPixelSpace, nLineSpace and nBandSpace can have arbitrary
    // values, there is no way of finding a unique(x,y,band) solution. We need
    // to restrict the space of possibilities strongly.
    // if nBandSpace >= nBufYSize * nLineSpace and
    //   nLineSpace >= nBufXSize * nPixelSpace,           INTERLEAVE = BAND
    //      band = OFFSET / nBandSpace
    //      y = (OFFSET - band * nBandSpace) / nLineSpace
    //      x = (OFFSET - band * nBandSpace - y * nLineSpace) / nPixelSpace
    // else if nPixelSpace >= nBandCount * nBandSpace and
    //   nLineSpace >= nBufXSize * nPixelSpace,    INTERLEAVE = PIXEL
    //      y = OFFSET / nLineSpace
    //      x = (OFFSET - y * nLineSpace) / nPixelSpace
    //      band = (OFFSET - y * nLineSpace - x * nPixelSpace) / nBandSpace

    if( nDataTypeSize == 0 || /* to please Coverity. not needed */
        nLineSpace < static_cast<GIntBig>(nBufXSize) * nPixelSpace ||
        (nBandCount > 1 &&
        (nBandSpace == nPixelSpace ||
        (nBandSpace < nPixelSpace &&
         (nBandSpace < nDataTypeSize ||
          nPixelSpace < nBandCount * nBandSpace)) ||
        (nBandSpace > nPixelSpace &&
         (nPixelSpace < nDataTypeSize ||
          nBandSpace < nBufYSize * nLineSpace)))) )
    {
        CPLError(
            CE_Failure, CPLE_NotSupported,
            "Only pixel interleaving or band interleaving are supported" );
        return nullptr;
    }

    /* Avoid odd spacings that would complicate I/O operations */
    /* Ensuring they are multiple of nDataTypeSize should be fine, because */
    /* the page size is a power of 2 that is also a multiple of nDataTypeSize */
    if( (nPixelSpace % nDataTypeSize) != 0 ||
        (nLineSpace % nDataTypeSize) != 0 ||
        (nBandSpace % nDataTypeSize) != 0 )
    {
        CPLError( CE_Failure, CPLE_NotSupported,
                  "Unsupported spacing" );
        return nullptr;
    }

    bool bIsBandSequential = nBandSpace >= nBufYSize * nLineSpace;
    if( bIsBandSequential )
        nReqMem = nBandCount * nBandSpace;
    else
        nReqMem = nBufYSize * nLineSpace;
    if( nReqMem != static_cast<GUIntBig>(static_cast<size_t>(nReqMem)) )
    {
        CPLError( CE_Failure, CPLE_OutOfMemory,
                  "Cannot reserve " CPL_FRMT_GUIB " bytes", nReqMem );
        return nullptr;
    }

    psParams = new GDALVirtualMem( hDS, hBand, nXOff, nYOff,
                                   nXSize, nYSize,
                                   nBufXSize, nBufYSize,
                                   eBufType,
                                   nBandCount, panBandMap,
                                   nPixelSpace,
                                   nLineSpace,
                                   nBandSpace );

    view = CPLVirtualMemNew(
        static_cast<size_t>(nReqMem),
        nCacheSize,
        nPageSizeHint,
        bSingleThreadUsage,
        eRWFlag == GF_Read ?
        VIRTUALMEM_READONLY_ENFORCED : VIRTUALMEM_READWRITE,
        bIsBandSequential ? GDALVirtualMem::FillCacheBandSequential :
                            GDALVirtualMem::FillCachePixelInterleaved,
        bIsBandSequential ? GDALVirtualMem::SaveFromCacheBandSequential :
                            GDALVirtualMem::SaveFromCachePixelInterleaved,
        GDALVirtualMem::Destroy,
        psParams );

    if( view == nullptr )
    {
        delete psParams;
    }

    return view;
}

/************************************************************************/
/*                       GDALDatasetGetVirtualMem()                     */
/************************************************************************/

/** Create a CPLVirtualMem object from a GDAL dataset object.
 *
 * Only supported on Linux for now.
 *
 * This method allows creating a virtual memory object for a region of one
 * or more GDALRasterBands from  this dataset. The content of the virtual
 * memory object is automatically filled from dataset content when a virtual
 * memory page is first accessed, and it is released (or flushed in case of a
 * "dirty" page) when the cache size limit has been reached.
 *
 * The pointer to access the virtual memory object is obtained with
 * CPLVirtualMemGetAddr(). It remains valid until CPLVirtualMemFree() is called.
 * CPLVirtualMemFree() must be called before the dataset object is destroyed.
 *
 * If p is such a pointer and base_type the C type matching eBufType, for
 * default values of spacing parameters, the element of image coordinates (x, y)
 * (relative to xOff, yOff) for band b can be accessed with
 * ((base_type*)p)[x + y * nBufXSize + (b-1)*nBufXSize*nBufYSize].
 *
 * Note that the mechanism used to transparently fill memory pages when they are
 * accessed is the same (but in a controlled way) than what occurs when a memory
 * error occurs in a program. Debugging software will generally interrupt
 * program execution when that happens. If needed, CPLVirtualMemPin() can be
 * used to avoid that by ensuring memory pages are allocated before being
 * accessed.
 *
 * The size of the region that can be mapped as a virtual memory object depends
 * on hardware and operating system limitations.
 * On Linux AMD64 platforms, the maximum value is 128 TB.
 * On Linux x86 platforms, the maximum value is 2 GB.
 *
 * Data type translation is automatically done if the data type
 * (eBufType) of the buffer is different than
 * that of the GDALRasterBand.
 *
 * Image decimation / replication is currently not supported, i.e. if the
 * size of the region being accessed (nXSize x nYSize) is different from the
 * buffer size (nBufXSize x nBufYSize).
 *
 * The nPixelSpace, nLineSpace and nBandSpace parameters allow reading into or
 * writing from various organization of buffers. Arbitrary values for the
 * spacing parameters are not supported. Those values must be multiple of the
 * size of thebuffer data type, and must be either band sequential
 * organization (typically nPixelSpace = GDALGetDataTypeSizeBytes(eBufType),
 * nLineSpace = nPixelSpace * nBufXSize,
 * nBandSpace = nLineSpace * nBufYSize), or pixel-interleaved organization
 * (typically nPixelSpace = nBandSpace * nBandCount,
 * nLineSpace = nPixelSpace * nBufXSize,
 * nBandSpace = GDALGetDataTypeSizeBytes(eBufType))
 *
 * @param hDS Dataset object
 *
 * @param eRWFlag Either GF_Read to read a region of data, or GF_Write to
 * write a region of data.
 *
 * @param nXOff The pixel offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the left side.
 *
 * @param nYOff The line offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the top.
 *
 * @param nXSize The width of the region of the band to be accessed in pixels.
 *
 * @param nYSize The height of the region of the band to be accessed in lines.
 *
 * @param nBufXSize the width of the buffer image into which the desired region
 * is to be read, or from which it is to be written.
 *
 * @param nBufYSize the height of the buffer image into which the desired
 * region is to be read, or from which it is to be written.
 *
 * @param eBufType the type of the pixel values in the data buffer. The
 * pixel values will automatically be translated to/from the GDALRasterBand
 * data type as needed.
 *
 * @param nBandCount the number of bands being read or written.
 *
 * @param panBandMap the list of nBandCount band numbers being read/written.
 * Note band numbers are 1 based. This may be NULL to select the first
 * nBandCount bands.
 *
 * @param nPixelSpace The byte offset from the start of one pixel value in
 * the buffer to the start of the next pixel value within a scanline. If
 * defaulted (0) the size of the datatype eBufType is used.
 *
 * @param nLineSpace The byte offset from the start of one scanline in
 * the buffer to the start of the next. If defaulted (0) the size of the
 * datatype eBufType * nBufXSize is used.
 *
 * @param nBandSpace the byte offset from the start of one bands data to the
 * start of the next. If defaulted (0) the value will be
 * nLineSpace * nBufYSize implying band sequential organization
 * of the data buffer.
 *
 * @param nCacheSize   size in bytes of the maximum memory that will be really
 *                     allocated (must ideally fit into RAM)
 *
 * @param nPageSizeHint hint for the page size. Must be a multiple of the
 *                      system page size, returned by CPLGetPageSize().
 *                      Minimum value is generally 4096. Might be set to 0 to
 *                      let the function determine a default page size.
 *
 * @param bSingleThreadUsage set to TRUE if there will be no concurrent threads
 *                           that will access the virtual memory mapping. This
 *                           can optimize performance a bit. If set to FALSE,
 *                           CPLVirtualMemDeclareThread() must be called.
 *
 * @param papszOptions NULL terminated list of options. Unused for now.
 *
 * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
 *         or NULL in case of failure.
 *
 * @since GDAL 1.11
 */

CPLVirtualMem* GDALDatasetGetVirtualMem( GDALDatasetH hDS,
                                         GDALRWFlag eRWFlag,
                                         int nXOff, int nYOff,
                                         int nXSize, int nYSize,
                                         int nBufXSize, int nBufYSize,
                                         GDALDataType eBufType,
                                         int nBandCount, int* panBandMap,
                                         int nPixelSpace,
                                         GIntBig nLineSpace,
                                         GIntBig nBandSpace,
                                         size_t nCacheSize,
                                         size_t nPageSizeHint,
                                         int bSingleThreadUsage,
                                         CSLConstList papszOptions )
{
    return GDALGetVirtualMem( hDS, nullptr, eRWFlag, nXOff, nYOff, nXSize, nYSize,
                              nBufXSize, nBufYSize, eBufType,
                              nBandCount, panBandMap,
                              nPixelSpace, nLineSpace, nBandSpace,
                              nCacheSize, nPageSizeHint, bSingleThreadUsage,
                              papszOptions );
}

/************************************************************************/
/*                     GDALRasterBandGetVirtualMem()                    */
/************************************************************************/

/** Create a CPLVirtualMem object from a GDAL raster band object.
 *
 * Only supported on Linux for now.
 *
 * This method allows creating a virtual memory object for a region of a
 * GDALRasterBand. The content of the virtual
 * memory object is automatically filled from dataset content when a virtual
 * memory page is first accessed, and it is released (or flushed in case of a
 * "dirty" page) when the cache size limit has been reached.
 *
 * The pointer to access the virtual memory object is obtained with
 * CPLVirtualMemGetAddr(). It remains valid until CPLVirtualMemFree() is called.
 * CPLVirtualMemFree() must be called before the raster band object is
 * destroyed.
 *
 * If p is such a pointer and base_type the C type matching eBufType, for
 * values of spacing parameters, the element of image coordinates (x, y)
 * default (relative to xOff, yOff) can be accessed with
 * ((base_type*)p)[x + y * nBufXSize].
 *
 * Note that the mechanism used to transparently fill memory pages when they are
 * accessed is the same (but in a controlled way) than what occurs when a memory
 * error occurs in a program. Debugging software will generally interrupt
 * program execution when that happens. If needed, CPLVirtualMemPin() can be
 * used to avoid that by ensuring memory pages are allocated before being
 * accessed.
 *
 * The size of the region that can be mapped as a virtual memory object depends
 * on hardware and operating system limitations.
 * On Linux AMD64 platforms, the maximum value is 128 TB.
 * On Linux x86 platforms, the maximum value is 2 GB.
 *
 * Data type translation is automatically done if the data type
 * (eBufType) of the buffer is different than
 * that of the GDALRasterBand.
 *
 * Image decimation / replication is currently not supported, i.e. if the
 * size of the region being accessed (nXSize x nYSize) is different from the
 * buffer size (nBufXSize x nBufYSize).
 *
 * The nPixelSpace and nLineSpace parameters allow reading into or
 * writing from various organization of buffers. Arbitrary values for the
 * spacing parameters are not supported. Those values must be multiple of the
 * size of the buffer data type and must be such that nLineSpace >=
 * nPixelSpace * nBufXSize.
 *
 * @param hBand Rasterband object
 *
 * @param eRWFlag Either GF_Read to read a region of data, or GF_Write to
 * write a region of data.
 *
 * @param nXOff The pixel offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the left side.
 *
 * @param nYOff The line offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the top.
 *
 * @param nXSize The width of the region of the band to be accessed in pixels.
 *
 * @param nYSize The height of the region of the band to be accessed in lines.
 *
 * @param nBufXSize the width of the buffer image into which the desired region
 * is to be read, or from which it is to be written.
 *
 * @param nBufYSize the height of the buffer image into which the desired
 * region is to be read, or from which it is to be written.
 *
 * @param eBufType the type of the pixel values in the data buffer. The
 * pixel values will automatically be translated to/from the GDALRasterBand
 * data type as needed.
 *
 * @param nPixelSpace The byte offset from the start of one pixel value in the
 * buffer to the start of the next pixel value within a scanline. If defaulted
 * (0) the size of the datatype eBufType is used.
 *
 * @param nLineSpace The byte offset from the start of one scanline in the
 * buffer to the start of the next. If defaulted (0) the size of the datatype
 * eBufType * nBufXSize is used.
 *
 * @param nCacheSize   size in bytes of the maximum memory that will be really
 *                     allocated (must ideally fit into RAM)
 *
 * @param nPageSizeHint hint for the page size. Must be a multiple of the
 *                      system page size, returned by CPLGetPageSize().
 *                      Minimum value is generally 4096. Might be set to 0 to
 *                      let the function determine a default page size.
 *
 * @param bSingleThreadUsage set to TRUE if there will be no concurrent threads
 *                           that will access the virtual memory mapping. This
 *                           can optimize performance a bit. If set to FALSE,
 *                           CPLVirtualMemDeclareThread() must be called.
 *
 * @param papszOptions NULL terminated list of options. Unused for now.
 *
 * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
 *         or NULL in case of failure.
 *
 * @since GDAL 1.11
 */

CPLVirtualMem* GDALRasterBandGetVirtualMem( GDALRasterBandH hBand,
                                            GDALRWFlag eRWFlag,
                                            int nXOff, int nYOff,
                                            int nXSize, int nYSize,
                                            int nBufXSize, int nBufYSize,
                                            GDALDataType eBufType,
                                            int nPixelSpace,
                                            GIntBig nLineSpace,
                                            size_t nCacheSize,
                                            size_t nPageSizeHint,
                                            int bSingleThreadUsage,
                                            CSLConstList papszOptions )
{
    return GDALGetVirtualMem( nullptr, hBand, eRWFlag, nXOff, nYOff,
                              nXSize, nYSize,
                              nBufXSize, nBufYSize, eBufType,
                              1, nullptr,
                              nPixelSpace, nLineSpace, 0,
                              nCacheSize, nPageSizeHint, bSingleThreadUsage,
                              papszOptions );
}

/************************************************************************/
/*                        GDALTiledVirtualMem                           */
/************************************************************************/

class GDALTiledVirtualMem
{
    GDALDatasetH hDS = nullptr;
    GDALRasterBandH hBand = nullptr;
    int nXOff = 0;
    int nYOff = 0;
    int nXSize = 0;
    int nYSize = 0;
    int nTileXSize = 0;
    int nTileYSize = 0;
    GDALDataType eBufType = GDT_Byte;
    int nBandCount = 0;
    int* panBandMap = nullptr;
    GDALTileOrganization eTileOrganization = GTO_TIP;

    void DoIO( GDALRWFlag eRWFlag, size_t nOffset,
               void* pPage, size_t nBytes ) const;

    CPL_DISALLOW_COPY_ASSIGN(GDALTiledVirtualMem)

public:
             GDALTiledVirtualMem( GDALDatasetH hDS,
                                  GDALRasterBandH hBand,
                                  int nXOff, int nYOff,
                                  int nXSize, int nYSize,
                                  int nTileXSize, int nTileYSize,
                                  GDALDataType eBufType,
                                  int nBandCount, const int* panBandMapIn,
                                  GDALTileOrganization eTileOrganization );
            ~GDALTiledVirtualMem();

    static void FillCache( CPLVirtualMem* ctxt,  size_t nOffset,
                           void* pPageToFill,
                           size_t nPageSize, void* pUserData );
    static void SaveFromCache( CPLVirtualMem* ctxt,  size_t nOffset,
                               const void* pPageToBeEvicted,
                               size_t nToEvicted, void* pUserData );

    static void Destroy( void* pUserData );
};

/************************************************************************/
/*                        GDALTiledVirtualMem()                         */
/************************************************************************/

GDALTiledVirtualMem::GDALTiledVirtualMem(
    GDALDatasetH hDSIn,
    GDALRasterBandH hBandIn,
    int nXOffIn, int nYOffIn,
    int nXSizeIn, int nYSizeIn,
    int nTileXSizeIn, int nTileYSizeIn,
    GDALDataType eBufTypeIn,
    int nBandCountIn, const int* panBandMapIn,
    GDALTileOrganization eTileOrganizationIn ) :
    hDS(hDSIn),
    hBand(hBandIn),
    nXOff(nXOffIn),
    nYOff(nYOffIn),
    nXSize(nXSizeIn),
    nYSize(nYSizeIn),
    nTileXSize(nTileXSizeIn),
    nTileYSize(nTileYSizeIn),
    eBufType(eBufTypeIn),
    nBandCount(nBandCountIn),
    eTileOrganization(eTileOrganizationIn)
{
    if( hDS != nullptr )
    {
        panBandMap = static_cast<int*>(CPLMalloc(nBandCount * sizeof(int)));
        if( panBandMapIn )
        {
            memcpy(panBandMap, panBandMapIn, nBandCount * sizeof(int));
        }
        else
        {
            for(int i = 0; i < nBandCount; i++ )
                panBandMap[i] = i + 1;
        }
    }
    else
    {
        panBandMap = nullptr;
        nBandCount = 1;
    }
}

/************************************************************************/
/*                       ~GDALTiledVirtualMem()                         */
/************************************************************************/

GDALTiledVirtualMem::~GDALTiledVirtualMem()
{
    CPLFree(panBandMap);
}

/************************************************************************/
/*                                DoIO()                                */
/************************************************************************/

void GDALTiledVirtualMem::DoIO( GDALRWFlag eRWFlag, size_t nOffset,
                                void* pPage, size_t nBytes ) const
{
    const int nDataTypeSize = GDALGetDataTypeSizeBytes(eBufType);
    int nTilesPerRow = (nXSize + nTileXSize - 1) / nTileXSize;
    int nTilesPerCol = (nYSize + nTileYSize - 1) / nTileYSize;
    size_t nPageSize = nTileXSize * nTileYSize * nDataTypeSize;
    if( eTileOrganization != GTO_BSQ )
        nPageSize *= nBandCount;
    CPLAssert((nOffset % nPageSize) == 0);
    CPLAssert(nBytes == nPageSize);
    size_t nTile = 0;
    int band = 0;
    int nPixelSpace = 0;
    int nLineSpace = 0;
    int nBandSpace = 0;
    if( eTileOrganization == GTO_TIP )
    {
        nTile = nOffset / nPageSize;
        band = 0;
        nPixelSpace = nDataTypeSize * nBandCount;
        nLineSpace = nPixelSpace * nTileXSize;
        nBandSpace = nDataTypeSize;
    }
    else if( eTileOrganization == GTO_BIT )
    {
        nTile = nOffset / nPageSize;
        band = 0;
        nPixelSpace = nDataTypeSize;
        nLineSpace = nPixelSpace * nTileXSize;
        nBandSpace = nLineSpace * nTileYSize;
    }
    else
    {
        // offset = nPageSize * (band * nTilesPerRow * nTilesPerCol + nTile)
        band = static_cast<int>(
            nOffset / (nPageSize * nTilesPerRow * nTilesPerCol));
        nTile = nOffset / nPageSize - band * nTilesPerRow * nTilesPerCol;
        nPixelSpace = nDataTypeSize;
        nLineSpace = nPixelSpace * nTileXSize;
        nBandSpace = 0;
        band ++;
    }
    size_t nYTile = nTile / nTilesPerRow;
    size_t nXTile = nTile - nYTile * nTilesPerRow;

    int nReqXSize = std::min( nTileXSize,
                              nXSize - static_cast<int>(nXTile * nTileXSize) );
    int nReqYSize = std::min( nTileYSize,
                              nYSize - static_cast<int>(nYTile * nTileYSize) );
    if( eRWFlag == GF_Read && (nReqXSize < nTileXSize ||
                               nReqYSize < nTileYSize) )
        memset(pPage, 0, nBytes);
    if( hDS != nullptr )
    {
        CPL_IGNORE_RET_VAL(GDALDatasetRasterIO(
            hDS, eRWFlag,
            static_cast<int>(nXOff + nXTile * nTileXSize),
            static_cast<int>(nYOff + nYTile * nTileYSize),
            nReqXSize, nReqYSize,
            pPage,
            nReqXSize, nReqYSize,
            eBufType,
            eTileOrganization != GTO_BSQ ? nBandCount : 1,
            eTileOrganization != GTO_BSQ ? panBandMap : &band,
            nPixelSpace, nLineSpace, nBandSpace ));
    }
    else
    {
        CPL_IGNORE_RET_VAL( GDALRasterIO(
            hBand, eRWFlag,
            static_cast<int>(nXOff + nXTile * nTileXSize),
            static_cast<int>(nYOff + nYTile * nTileYSize),
            nReqXSize, nReqYSize,
            pPage,
            nReqXSize, nReqYSize,
            eBufType,
            nPixelSpace, nLineSpace ) );
    }
}

/************************************************************************/
/*                           FillCache()                                */
/************************************************************************/

void GDALTiledVirtualMem::FillCache( CPLVirtualMem*,
                                     size_t nOffset,
                                     void* pPageToFill,
                                     size_t nToFill,
                                     void* pUserData)
{
    const GDALTiledVirtualMem* psParams =
        static_cast<GDALTiledVirtualMem *>( pUserData );
    psParams->DoIO(GF_Read, nOffset, pPageToFill, nToFill);
}

/************************************************************************/
/*                          SaveFromCache()                             */
/************************************************************************/

void GDALTiledVirtualMem::SaveFromCache( CPLVirtualMem*,
                                         size_t nOffset,
                                         const void* pPageToBeEvicted,
                                         size_t nToEvicted, void* pUserData)
{
    const GDALTiledVirtualMem* psParams =
        static_cast<GDALTiledVirtualMem *>( pUserData );
    psParams->DoIO( GF_Write, nOffset,
                   const_cast<void *>(pPageToBeEvicted),
                   nToEvicted );
}

/************************************************************************/
/*                                Destroy()                             */
/************************************************************************/

void GDALTiledVirtualMem::Destroy( void* pUserData )
{
    GDALTiledVirtualMem* psParams =
        static_cast<GDALTiledVirtualMem*>( pUserData );
    delete psParams;
}

/************************************************************************/
/*                      GDALGetTiledVirtualMem()                        */
/************************************************************************/

static CPLVirtualMem* GDALGetTiledVirtualMem(
    GDALDatasetH hDS,
    GDALRasterBandH hBand,
    GDALRWFlag eRWFlag,
    int nXOff, int nYOff,
    int nXSize, int nYSize,
    int nTileXSize, int nTileYSize,
    GDALDataType eBufType,
    int nBandCount, int* panBandMap,
    GDALTileOrganization eTileOrganization,
    size_t nCacheSize,
    int bSingleThreadUsage,
    CSLConstList /* papszOptions */ )
{
    CPLVirtualMem* view;
    GDALTiledVirtualMem* psParams;

    size_t nPageSize = CPLGetPageSize();
    if( nPageSize == 0 )
    {
        CPLError(
            CE_Failure, CPLE_NotSupported,
            "GDALGetTiledVirtualMem() unsupported on this "
            "operating system / configuration" );
        return nullptr;
    }

    int nRasterXSize =
        hDS ? GDALGetRasterXSize(hDS) : GDALGetRasterBandXSize(hBand);
    int nRasterYSize =
        hDS ? GDALGetRasterYSize(hDS) : GDALGetRasterBandYSize(hBand);

    if( nXOff < 0 || nYOff < 0 ||
        nTileXSize <= 0 || nTileYSize <= 0 ||
        nXOff + nXSize > nRasterXSize ||
        nYOff + nYSize > nRasterYSize )
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Invalid window request");
        return nullptr;
    }

    if( hDS != nullptr && !GDALCheckBandParameters(hDS, nBandCount, panBandMap ) )
        return nullptr;

    const int nDataTypeSize = GDALGetDataTypeSizeBytes(eBufType);
    int nTilesPerRow = (nXSize + nTileXSize - 1) / nTileXSize;
    int nTilesPerCol = (nYSize + nTileYSize - 1) / nTileYSize;
    GUIntBig nReqMem = static_cast<GUIntBig>(nTilesPerRow) * nTilesPerCol *
                        nTileXSize * nTileYSize * nBandCount * nDataTypeSize;
    if( nReqMem != static_cast<GUIntBig>(static_cast<size_t>(nReqMem)) )
    {
        CPLError( CE_Failure, CPLE_OutOfMemory,
                  "Cannot reserve " CPL_FRMT_GUIB " bytes", nReqMem );
        return nullptr;
    }

    size_t nPageSizeHint = nTileXSize * nTileYSize * nDataTypeSize;
    if( eTileOrganization != GTO_BSQ )
        nPageSizeHint *= nBandCount;
    if( (nPageSizeHint % nPageSize) != 0 )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "Tile dimensions incompatible with page size");
        return nullptr;
    }

    psParams = new GDALTiledVirtualMem( hDS, hBand, nXOff, nYOff,
                                        nXSize, nYSize,
                                        nTileXSize, nTileYSize,
                                        eBufType,
                                        nBandCount, panBandMap,
                                        eTileOrganization );

    view = CPLVirtualMemNew(
        static_cast<size_t>(nReqMem),
        nCacheSize,
        nPageSizeHint,
        bSingleThreadUsage,
        eRWFlag == GF_Read ?
        VIRTUALMEM_READONLY_ENFORCED : VIRTUALMEM_READWRITE,
        GDALTiledVirtualMem::FillCache,
        GDALTiledVirtualMem::SaveFromCache,
        GDALTiledVirtualMem::Destroy,
        psParams );

    if( view == nullptr )
    {
        delete psParams;
    }
    else if( CPLVirtualMemGetPageSize(view) != nPageSizeHint )
    {
        CPLError(
            CE_Failure, CPLE_AppDefined,
            "Did not get expected page size : %d vs %d",
            static_cast<int>(CPLVirtualMemGetPageSize(view)),
            static_cast<int>(nPageSizeHint) );
        CPLVirtualMemFree(view);
        return nullptr;
    }

    return view;
}

/************************************************************************/
/*                   GDALDatasetGetTiledVirtualMem()                    */
/************************************************************************/

/** Create a CPLVirtualMem object from a GDAL dataset object, with tiling
 * organization
 *
 * Only supported on Linux for now.
 *
 * This method allows creating a virtual memory object for a region of one
 * or more GDALRasterBands from  this dataset. The content of the virtual
 * memory object is automatically filled from dataset content when a virtual
 * memory page is first accessed, and it is released (or flushed in case of a
 * "dirty" page) when the cache size limit has been reached.
 *
 * Contrary to GDALDatasetGetVirtualMem(), pixels will be organized by tiles
 * instead of scanlines. Different ways of organizing pixel within/across tiles
 * can be selected with the eTileOrganization parameter.
 *
 * If nXSize is not a multiple of nTileXSize or nYSize is not a multiple of
 * nTileYSize, partial tiles will exists at the right and/or bottom of the
 * region of interest. Those partial tiles will also have nTileXSize *
 * nTileYSize dimension, with padding pixels.
 *
 * The pointer to access the virtual memory object is obtained with
 * CPLVirtualMemGetAddr(). It remains valid until CPLVirtualMemFree() is called.
 * CPLVirtualMemFree() must be called before the dataset object is destroyed.
 *
 * If p is such a pointer and base_type the C type matching eBufType, for
 * default values of spacing parameters, the element of image coordinates (x, y)
 * (relative to xOff, yOff) for band b can be accessed with:
 *  - for eTileOrganization = GTO_TIP,
 *        ((base_type*)p)[tile_number(x,y)*nBandCount*tile_size +
 *                        offset_in_tile(x,y)*nBandCount + (b-1)].
 *  - for eTileOrganization = GTO_BIT,
 *        ((base_type*)p)[(tile_number(x,y)*nBandCount +
 *                        (b-1)) * tile_size + offset_in_tile(x,y)].
 *  - for eTileOrganization = GTO_BSQ,
 *        ((base_type*)p)[(tile_number(x,y) +
 *                        (b-1)*nTilesCount) * tile_size + offset_in_tile(x,y)].
 *
 * where nTilesPerRow = ceil(nXSize / nTileXSize)
 *       nTilesPerCol = ceil(nYSize / nTileYSize)
 *       nTilesCount = nTilesPerRow * nTilesPerCol
 *       tile_number(x,y) = (y / nTileYSize) * nTilesPerRow + (x / nTileXSize)
 *       offset_in_tile(x,y) = (y % nTileYSize) * nTileXSize  + (x % nTileXSize)
 *       tile_size = nTileXSize * nTileYSize
 *
 * Note that for a single band request, all tile organizations are equivalent.
 *
 * Note that the mechanism used to transparently fill memory pages when they are
 * accessed is the same (but in a controlled way) than what occurs when a memory
 * error occurs in a program. Debugging software will generally interrupt
 * program execution when that happens. If needed, CPLVirtualMemPin() can be
 * used to avoid that by ensuring memory pages are allocated before being
 * accessed.
 *
 * The size of the region that can be mapped as a virtual memory object depends
 * on hardware and operating system limitations.
 * On Linux AMD64 platforms, the maximum value is 128 TB.
 * On Linux x86 platforms, the maximum value is 2 GB.
 *
 * Data type translation is automatically done if the data type
 * (eBufType) of the buffer is different than
 * that of the GDALRasterBand.
 *
 * @param hDS Dataset object
 *
 * @param eRWFlag Either GF_Read to read a region of data, or GF_Write to
 * write a region of data.
 *
 * @param nXOff The pixel offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the left side.
 *
 * @param nYOff The line offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the top.
 *
 * @param nXSize The width of the region of the band to be accessed in pixels.
 *
 * @param nYSize The height of the region of the band to be accessed in lines.
 *
 * @param nTileXSize the width of the tiles.
 *
 * @param nTileYSize the height of the tiles.
 *
 * @param eBufType the type of the pixel values in the data buffer. The
 * pixel values will automatically be translated to/from the GDALRasterBand
 * data type as needed.
 *
 * @param nBandCount the number of bands being read or written.
 *
 * @param panBandMap the list of nBandCount band numbers being read/written.
 * Note band numbers are 1 based. This may be NULL to select the first
 * nBandCount bands.
 *
 * @param eTileOrganization tile organization.
 *
 * @param nCacheSize   size in bytes of the maximum memory that will be really
 *                     allocated (must ideally fit into RAM)
 *
 * @param bSingleThreadUsage set to TRUE if there will be no concurrent threads
 *                           that will access the virtual memory mapping. This
 *                           can optimize performance a bit. If set to FALSE,
 *                           CPLVirtualMemDeclareThread() must be called.
 *
 * @param papszOptions NULL terminated list of options. Unused for now.
 *
 * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
 *         or NULL in case of failure.
 *
 * @since GDAL 1.11
 */

CPLVirtualMem* GDALDatasetGetTiledVirtualMem(
    GDALDatasetH hDS,
    GDALRWFlag eRWFlag,
    int nXOff, int nYOff,
    int nXSize, int nYSize,
    int nTileXSize, int nTileYSize,
    GDALDataType eBufType,
    int nBandCount, int* panBandMap,
    GDALTileOrganization eTileOrganization,
    size_t nCacheSize,
    int bSingleThreadUsage,
    CSLConstList papszOptions )
{
    return GDALGetTiledVirtualMem( hDS, nullptr, eRWFlag, nXOff, nYOff,
                                   nXSize, nYSize, nTileXSize, nTileYSize,
                                   eBufType, nBandCount, panBandMap,
                                   eTileOrganization,
                                   nCacheSize, bSingleThreadUsage,
                                   papszOptions );
}

/************************************************************************/
/*                   GDALRasterBandGetTiledVirtualMem()                 */
/************************************************************************/

/** Create a CPLVirtualMem object from a GDAL rasterband object, with tiling
 * organization
 *
 * Only supported on Linux for now.
 *
 * This method allows creating a virtual memory object for a region of one
 * GDALRasterBand. The content of the virtual
 * memory object is automatically filled from dataset content when a virtual
 * memory page is first accessed, and it is released (or flushed in case of a
 * "dirty" page) when the cache size limit has been reached.
 *
 * Contrary to GDALDatasetGetVirtualMem(), pixels will be organized by tiles
 * instead of scanlines.
 *
 * If nXSize is not a multiple of nTileXSize or nYSize is not a multiple of
 * nTileYSize, partial tiles will exists at the right and/or bottom of the
 * region of interest. Those partial tiles will also have nTileXSize *
 * nTileYSize dimension, with padding pixels.
 *
 * The pointer to access the virtual memory object is obtained with
 * CPLVirtualMemGetAddr(). It remains valid until CPLVirtualMemFree() is called.
 * CPLVirtualMemFree() must be called before the raster band object is
 * destroyed.
 *
 * If p is such a pointer and base_type the C type matching eBufType, for
 * default values of spacing parameters, the element of image coordinates (x, y)
 * (relative to xOff, yOff) can be accessed with:
 *  ((base_type*)p)[tile_number(x,y)*tile_size + offset_in_tile(x,y)].
 *
 * where nTilesPerRow = ceil(nXSize / nTileXSize)
 *       nTilesCount = nTilesPerRow * nTilesPerCol
 *       tile_number(x,y) = (y / nTileYSize) * nTilesPerRow + (x / nTileXSize)
 *       offset_in_tile(x,y) = (y % nTileYSize) * nTileXSize  + (x % nTileXSize)
 *       tile_size = nTileXSize * nTileYSize
 *
 * Note that the mechanism used to transparently fill memory pages when they are
 * accessed is the same (but in a controlled way) than what occurs when a memory
 * error occurs in a program. Debugging software will generally interrupt
 * program execution when that happens. If needed, CPLVirtualMemPin() can be
 * used to avoid that by ensuring memory pages are allocated before being
 * accessed.
 *
 * The size of the region that can be mapped as a virtual memory object depends
 * on hardware and operating system limitations.
 * On Linux AMD64 platforms, the maximum value is 128 TB.
 * On Linux x86 platforms, the maximum value is 2 GB.
 *
 * Data type translation is automatically done if the data type
 * (eBufType) of the buffer is different than
 * that of the GDALRasterBand.
 *
 * @param hBand Rasterband object
 *
 * @param eRWFlag Either GF_Read to read a region of data, or GF_Write to
 * write a region of data.
 *
 * @param nXOff The pixel offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the left side.
 *
 * @param nYOff The line offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the top.
 *
 * @param nXSize The width of the region of the band to be accessed in pixels.
 *
 * @param nYSize The height of the region of the band to be accessed in lines.
 *
 * @param nTileXSize the width of the tiles.
 *
 * @param nTileYSize the height of the tiles.
 *
 * @param eBufType the type of the pixel values in the data buffer. The
 * pixel values will automatically be translated to/from the GDALRasterBand
 * data type as needed.
 *
 * @param nCacheSize   size in bytes of the maximum memory that will be really
 *                     allocated (must ideally fit into RAM)
 *
 * @param bSingleThreadUsage set to TRUE if there will be no concurrent threads
 *                           that will access the virtual memory mapping. This
 *                           can optimize performance a bit. If set to FALSE,
 *                           CPLVirtualMemDeclareThread() must be called.
 *
 * @param papszOptions NULL terminated list of options. Unused for now.
 *
 * @return a virtual memory object that must be freed by CPLVirtualMemFree(),
 *         or NULL in case of failure.
 *
 * @since GDAL 1.11
 */

CPLVirtualMem* GDALRasterBandGetTiledVirtualMem( GDALRasterBandH hBand,
                                                 GDALRWFlag eRWFlag,
                                                 int nXOff, int nYOff,
                                                 int nXSize, int nYSize,
                                                 int nTileXSize, int nTileYSize,
                                                 GDALDataType eBufType,
                                                 size_t nCacheSize,
                                                 int bSingleThreadUsage,
                                                 CSLConstList papszOptions )
{
    return GDALGetTiledVirtualMem( nullptr, hBand, eRWFlag, nXOff, nYOff,
                                   nXSize, nYSize, nTileXSize, nTileYSize,
                                   eBufType, 1, nullptr,
                                   GTO_BSQ,
                                   nCacheSize, bSingleThreadUsage,
                                   papszOptions );
}