In the resize method under win32 you have something
like this:

	/* Move to the desired EOF position */
        SetFilePointer (self->file_handle,
                new_size, NULL, FILE_BEGIN);
        /* Change the size of the file */
        SetEndOfFile (self->file_handle);

Which resizes the file

Under Unix you need to call 

   ftruncate(self->fileno, new_size)

before calling remap() to make it do the same thing.