ASSERT(WriteOffset.QuadPart + Length <= Fcb->RFCB.AllocationSize.QuadPart);
   ASSERT(WriteOffset.u.LowPart % BytesPerSector == 0);
   ASSERT(Length % BytesPerSector == 0);

   // Is this a write of the volume ?
   if (Fcb->Flags & FCB_IS_VOLUME)
   {
      Status = VfatWriteDiskPartial(IrpContext, &WriteOffset, Length, 0, TRUE);
      if (!NT_SUCCESS(Status))
      {
         DPRINT1("Volume writing failed, Status %x\n", Status);
      }
      return Status;
   }

   // Is this a write to the FAT ?
   if (Fcb->Flags & FCB_IS_FAT)
   {
      WriteOffset.u.LowPart += DeviceExt->FatInfo.FATStart * BytesPerSector;
      IrpContext->RefCount = 1;
      for (Count = 0; Count < DeviceExt->FatInfo.FATCount; Count++)
      {
         Status = VfatWriteDiskPartial(IrpContext, &WriteOffset, Length, 0, FALSE);
         if (!NT_SUCCESS(Status) && Status != STATUS_PENDING)
         {
            DPRINT1("FAT writing failed, Status %x\n", Status);
	    break;
         }
	 WriteOffset.u.LowPart += Fcb->RFCB.FileSize.u.LowPart;
      }
      if (0 != InterlockedDecrement((PLONG)&IrpContext->RefCount))
        {
	  KeWaitForSingleObject(&IrpContext->Event, Executive, KernelMode, FALSE, NULL);
	}
      if (NT_SUCCESS(Status) || Status == STATUS_PENDING)
        {
	  Status = IrpContext->Irp->IoStatus.Status;
	}
      return Status;
   }

   /*
    * Find the first cluster
    */
   FirstCluster = CurrentCluster =
      vfatDirEntryGetFirstCluster (DeviceExt, &Fcb->entry);

   if (FirstCluster == 1)
   {
      ASSERT(WriteOffset.u.LowPart + Length <= DeviceExt->FatInfo.rootDirectorySectors * BytesPerSector);
      // Directory of FAT12/16 needs a special handling
      WriteOffset.u.LowPart += DeviceExt->FatInfo.rootStart * BytesPerSector;
      // Fire up the write command
      Status = VfatWriteDiskPartial (IrpContext, &WriteOffset, Length, 0, TRUE);
      return Status;
   }

   ExAcquireFastMutex(&Fcb->LastMutex);
   LastCluster = Fcb->LastCluster;
   LastOffset = Fcb->LastOffset;
   ExReleaseFastMutex(&Fcb->LastMutex);

   /*
    * Find the cluster to start the write from
    */
   if (LastCluster > 0 && WriteOffset.u.LowPart >= LastOffset)
   {
      Status = OffsetToCluster(DeviceExt, LastCluster,
                               ROUND_DOWN(WriteOffset.u.LowPart, BytesPerCluster) -
                               LastOffset,
                               &CurrentCluster, FALSE);
#ifdef DEBUG_VERIFY_OFFSET_CACHING
      /* DEBUG VERIFICATION */
      {
         ULONG CorrectCluster;
         OffsetToCluster(DeviceExt, FirstCluster,
                         ROUND_DOWN(WriteOffset.u.LowPart, BytesPerCluster),
                         &CorrectCluster, FALSE);
         if (CorrectCluster != CurrentCluster)
            KEBUGCHECK(FAT_FILE_SYSTEM);
      }
#endif
   }
   else
   {
      Status = OffsetToCluster(DeviceExt, FirstCluster,
                               ROUND_DOWN(WriteOffset.u.LowPart, BytesPerCluster),
                               &CurrentCluster, FALSE);
   }

   if (!NT_SUCCESS(Status))
   {
      return(Status);
   }

   ExAcquireFastMutex(&Fcb->LastMutex);
   Fcb->LastCluster = CurrentCluster;
   Fcb->LastOffset = ROUND_DOWN (WriteOffset.u.LowPart, BytesPerCluster);
   ExReleaseFastMutex(&Fcb->LastMutex);

   IrpContext->RefCount = 1;
   BufferOffset = 0;

   while (Length > 0 && CurrentCluster != 0xffffffff)
   {
      StartCluster = CurrentCluster;
      StartOffset.QuadPart = ClusterToSector(DeviceExt, StartCluster) * BytesPerSector;
      BytesDone = 0;
      ClusterCount = 0;

      do
      {
         ClusterCount++;
         if (First)
         {
            BytesDone =  min (Length, BytesPerCluster - (WriteOffset.u.LowPart % BytesPerCluster));
	    StartOffset.QuadPart += WriteOffset.u.LowPart % BytesPerCluster;
      	    First = FALSE;
         }
         else
         {
      	    if (Length - BytesDone > BytesPerCluster)
      	    {
      	       BytesDone += BytesPerCluster;
      	    }
      	    else
      	    {
      	       BytesDone = Length;
      	    }
         }
         Status = NextCluster(DeviceExt, FirstCluster, &CurrentCluster, FALSE);
      }
      while (StartCluster + ClusterCount == CurrentCluster && NT_SUCCESS(Status) && Length > BytesDone);
      DPRINT("start %08x, next %08x, count %d\n",
             StartCluster, CurrentCluster, ClusterCount);

      ExAcquireFastMutex(&Fcb->LastMutex);
      Fcb->LastCluster = StartCluster + (ClusterCount - 1);
      Fcb->LastOffset = ROUND_DOWN(WriteOffset.u.LowPart, BytesPerCluster) + (ClusterCount - 1) * BytesPerCluster;
      ExReleaseFastMutex(&Fcb->LastMutex);

      // Fire up the write command
      Status = VfatWriteDiskPartial (IrpContext, &StartOffset, BytesDone, BufferOffset, FALSE);
      if (!NT_SUCCESS(Status) && Status != STATUS_PENDING)
        {
	  break;
	}
      BufferOffset += BytesDone;
      Length -= BytesDone;
      WriteOffset.u.LowPart += BytesDone;
   }
   if (0 != InterlockedDecrement((PLONG)&IrpContext->RefCount))
     {
       KeWaitForSingleObject(&IrpContext->Event, Executive, KernelMode, FALSE, NULL);
     }
   if (NT_SUCCESS(Status) || Status == STATUS_PENDING)
     {
       if (Length > 0)
         {
	   Status = STATUS_UNSUCCESSFUL;
	 }
       else
         {
	   Status = IrpContext->Irp->IoStatus.Status;
	 }
     }
   return Status;
}

NTSTATUS
VfatRead(PVFAT_IRP_CONTEXT IrpContext)
{
   NTSTATUS Status;
   PVFATFCB Fcb;
   ULONG Length = 0;
   ULONG ReturnedLength = 0;
   PERESOURCE Resource = NULL;
   LARGE_INTEGER ByteOffset;
   PVOID Buffer;
   PDEVICE_OBJECT DeviceToVerify;
   ULONG BytesPerSector;

   ASSERT(IrpContext);

   DPRINT("VfatRead(IrpContext %x)\n", IrpContext);

   ASSERT(IrpContext->DeviceObject);

   // This request is not allowed on the main device object
   if (IrpContext->DeviceObject == VfatGlobalData->DeviceObject)
   {
      DPRINT("VfatRead is called with the main device object.\n");
      Status = STATUS_INVALID_DEVICE_REQUEST;
      goto ByeBye;
   }

   ASSERT(IrpContext->DeviceExt);
   ASSERT(IrpContext->FileObject);
   Fcb = IrpContext->FileObject->FsContext;
   ASSERT(Fcb);

   DPRINT("<%wZ>\n", &Fcb->PathNameU);

   if (Fcb->Flags & FCB_IS_PAGE_FILE)
   {
      PFATINFO FatInfo = &IrpContext->DeviceExt->FatInfo;
      IrpContext->Stack->Parameters.Read.ByteOffset.QuadPart += FatInfo->dataStart * FatInfo->BytesPerSector;
      IoSkipCurrentIrpStackLocation(IrpContext->Irp);
      DPRINT("Read from page file, disk offset %I64x\n", IrpContext->Stack->Parameters.Read.ByteOffset.QuadPart);
      Status = IoCallDriver(IrpContext->DeviceExt->StorageDevice, IrpContext->Irp);
      VfatFreeIrpContext(IrpContext);
      return Status;
   }

   ByteOffset = IrpContext->Stack->Parameters.Read.ByteOffset;
   Length = IrpContext->Stack->Parameters.Read.Length;
   BytesPerSector = IrpContext->DeviceExt->FatInfo.BytesPerSector;

   /* fail if file is a directory and no paged read */
   if (*Fcb->Attributes & FILE_ATTRIBUTE_DIRECTORY && !(IrpContext->Irp->Flags & IRP_PAGING_IO))
   {
      Status = STATUS_INVALID_PARAMETER;
      goto ByeBye;
   }


   DPRINT("'%wZ', Offset: %d, Length %d\n", &Fcb->PathNameU, ByteOffset.u.LowPart, Length);

   if (ByteOffset.u.HighPart && !(Fcb->Flags & FCB_IS_VOLUME))
   {
      Status = STATUS_INVALID_PARAMETER;
      goto ByeBye;
   }
   if (ByteOffset.QuadPart >= Fcb->RFCB.FileSize.QuadPart)
   {
      IrpContext->Irp->IoStatus.Information = 0;
      Status = STATUS_END_OF_FILE;
      goto ByeBye;
   }
   if (IrpContext->Irp->Flags & (IRP_PAGING_IO | IRP_NOCACHE) || (Fcb->Flags & FCB_IS_VOLUME))
   {
      if (ByteOffset.u.LowPart % BytesPerSector != 0 || Length % BytesPerSector != 0)
      {
         DPRINT("%d %d\n", ByteOffset.u.LowPart, Length);
         // non cached read must be sector aligned
         Status = STATUS_INVALID_PARAMETER;
         goto ByeBye;
      }
   }
   if (Length == 0)
   {
      IrpContext->Irp->IoStatus.Information = 0;
      Status = STATUS_SUCCESS;
      goto ByeBye;
   }

   if (Fcb->Flags & FCB_IS_VOLUME)
   {
      Resource = &IrpContext->DeviceExt->DirResource;
   }
   else if (IrpContext->Irp->Flags & IRP_PAGING_IO)
   {
      Resource = &Fcb->PagingIoResource;
   }
   else
   {
      Resource = &Fcb->MainResource;
   }
   if (!ExAcquireResourceSharedLite(Resource,
                                    IrpContext->Flags & IRPCONTEXT_CANWAIT ? TRUE : FALSE))
   {
      Resource = NULL;
      Status = STATUS_PENDING;
      goto ByeBye;
   }

   if (!(IrpContext->Irp->Flags & IRP_PAGING_IO) &&
      FsRtlAreThereCurrentFileLocks(&Fcb->FileLock))
   {
      if (!FsRtlCheckLockForReadAccess(&Fcb->FileLock, IrpContext->Irp))
      {
         Status = STATUS_FILE_LOCK_CONFLICT;
         goto ByeBye;
      }
   }

   Buffer = VfatGetUserBuffer(IrpContext->Irp);
   if (!Buffer)
     {
       Status = STATUS_INVALID_USER_BUFFER;
       goto ByeBye;
     }

   if (!(IrpContext->Irp->Flags & (IRP_NOCACHE|IRP_PAGING_IO)) &&
     !(Fcb->Flags & (FCB_IS_PAGE_FILE|FCB_IS_VOLUME)))
   {
      // cached read
      CHECKPOINT;
      Status = STATUS_SUCCESS;
      if (ByteOffset.u.LowPart + Length > Fcb->RFCB.FileSize.u.LowPart)
      {
         Length = Fcb->RFCB.FileSize.u.LowPart - ByteOffset.u.LowPart;
         Status = /*STATUS_END_OF_FILE*/STATUS_SUCCESS;
      }

      CHECKPOINT;
      if (IrpContext->FileObject->PrivateCacheMap == NULL)
      {
#ifdef USE_ROS_CC_AND_FS
        ULONG CacheSize;
        CacheSize = max(IrpContext->DeviceExt->FatInfo.BytesPerCluster,
                        8 * PAGE_SIZE);
        CcRosInitializeFileCache(IrpContext->FileObject, CacheSize);
#else
        /* FIXME: Guard by SEH. */
        CcInitializeCacheMap(IrpContext->FileObject,
                             (PCC_FILE_SIZES)(&Fcb->RFCB.AllocationSize),
                             FALSE,
                             &(VfatGlobalData->CacheMgrCallbacks),
                             Fcb);
#endif
      }
      if (!CcCopyRead(IrpContext->FileObject, &ByteOffset, Length,
                      (BOOLEAN)(IrpContext->Flags & IRPCONTEXT_CANWAIT), Buffer,
                      &IrpContext->Irp->IoStatus))
      {
         Status = STATUS_PENDING;
         goto ByeBye;
      }
      CHECKPOINT;
      if (!NT_SUCCESS(IrpContext->Irp->IoStatus.Status))
      {
        Status = IrpContext->Irp->IoStatus.Status;
      }
   }
   else
   {
      // non cached read
      CHECKPOINT;
      if (ByteOffset.QuadPart + Length > ROUND_UP(Fcb->RFCB.FileSize.QuadPart, BytesPerSector))
      {
         Length = (ULONG)(ROUND_UP(Fcb->RFCB.FileSize.QuadPart, BytesPerSector) - ByteOffset.QuadPart);
      }

      Status = VfatLockUserBuffer(IrpContext->Irp, Length, IoWriteAccess);
      if (!NT_SUCCESS(Status))
        {
          goto ByeBye;
        }

      Status = VfatReadFileData(IrpContext, Length, ByteOffset, &ReturnedLength);
/**/
      if (Status == STATUS_VERIFY_REQUIRED)
      {
         DPRINT("VfatReadFile returned STATUS_VERIFY_REQUIRED\n");
         DeviceToVerify = IoGetDeviceToVerify(PsGetCurrentThread());
         IoSetDeviceToVerify(PsGetCurrentThread(), DeviceToVerify);
         Status = IoVerifyVolume (DeviceToVerify, FALSE);

         if (NT_SUCCESS(Status))
         {
            Status = VfatReadFileData(IrpContext, Length,
                                      ByteOffset, &ReturnedLength);
         }