public override int CopyPage(I4KbBatchWrites destI4KbBatchWrites, long pageNumber, PagerState pagerState)
{
long sizeToMap = AllocationGranularity;
var distanceFromStart = (pageNumber % NumberOfPagesInAllocationGranularity);
var allocationStartPosition = pageNumber - distanceFromStart;
var offset = allocationStartPosition * Constants.Storage.PageSize;
var mmflags = _copyOnWriteMode ? MmapFlags.MAP_PRIVATE : MmapFlags.MAP_SHARED;
var result = Syscall.mmap64(IntPtr.Zero, (UIntPtr)sizeToMap,
MmapProts.PROT_READ | MmapProts.PROT_WRITE,
mmflags, _fd, offset);
try
{
if (result.ToInt64() == -1) //system didn't succeed in mapping the address where we wanted
{
var err = Marshal.GetLastWin32Error();
Syscall.ThrowLastError(err,
$"Unable to map (default view size) {sizeToMap/Constants.Size.Kilobyte:#,#0} kb for page {pageNumber} starting at {allocationStartPosition} on {FileName}");
}
var pageHeader = (PageHeader *)(result.ToInt64() + distanceFromStart * Constants.Storage.PageSize);
int numberOfPages = 1;
if ((pageHeader->Flags & PageFlags.Overflow) == PageFlags.Overflow)
{
numberOfPages = VirtualPagerLegacyExtensions.GetNumberOfOverflowPages(pageHeader->OverflowSize);
}
if (numberOfPages + distanceFromStart > NumberOfPagesInAllocationGranularity)
{
Syscall.munmap(result, (UIntPtr)sizeToMap);
result = new IntPtr(-1);
sizeToMap = NearestSizeToAllocationGranularity((numberOfPages + distanceFromStart) *
Constants.Storage.PageSize);
result = Syscall.mmap64(IntPtr.Zero, (UIntPtr)sizeToMap, MmapProts.PROT_READ | MmapProts.PROT_WRITE,
mmflags, _fd, offset);
if (result.ToInt64() == -1)
{
var err = Marshal.GetLastWin32Error();
Syscall.ThrowLastError(err,
$"Unable to map {sizeToMap/Constants.Size.Kilobyte:#,#0} kb for page {pageNumber} starting at {allocationStartPosition} on {FileName}");
}
pageHeader = (PageHeader *)(result.ToInt64() + (distanceFromStart * Constants.Storage.PageSize));
}
const int adjustPageSize = (Constants.Storage.PageSize) / (4 * Constants.Size.Kilobyte);
destI4KbBatchWrites.Write(pageHeader->PageNumber * adjustPageSize, numberOfPages * adjustPageSize,
(byte *)pageHeader);
return(numberOfPages);
}
finally
{
if (result.ToInt64() != -1)
{
Syscall.munmap(result, (UIntPtr)sizeToMap);
}
}
}