writefile写入u盘无效，getlasterror为5，需锁定U盘

hFile := CreateFile(PChar(fileName), GENERIC_READ or GENERIC_WRITE, FILE_SHARE_READ or FILE_SHARE_WRITE, nil, OPEN_EXISTING, 0, 0);

//此循环是用于锁定要弹出的U盘设备，如果U盘在使用，则循环等待 for nTryCount := 0 to LOCK_RETRIES-1 do begin b:=DeviceIoControl(hFile,FSCTL_LOCK_VOLUME,nil,0,nil,0,dwBytesReturned,nil); if b=True then begin Break; end; end;