nova 根据conf动态加载虚拟化驱动

在nova/virt/driver.py 中的ComputeDriver 类中定义了load_compute_driver来加载用于虚拟化的driver。def load_compute_driver(virtapi, compute_driver=None):    """Load a compute driver module.    Load the compute driver module specified by the compute_driver    configuration option or, if supplied, the driver name supplied as an    argument.    Compute drivers constructors take a VirtAPI object as their first object    and this must be supplied.    :param virtapi: a VirtAPI instance    :param compute_driver: a compute driver name to override the config opt    :returns: a ComputeDriver instance    """    if not compute_driver:        compute_driver = CONF.compute_driver    if not compute_driver:        LOG.error(_LE("Compute driver option required, but not specified"))        sys.exit(1)    LOG.info(_LI("Loading compute driver '%s'"), compute_driver)    try:        driver = importutils.import_object(            'nova.virt.%s' % compute_driver,            virtapi)        return utils.check_isinstance(driver, ComputeDriver)    except ImportError:        LOG.exception(_LE("Unable to load the virtualization driver"))        sys.exit(1)可以compute_driver 是在CONF.compute_driver得到的,本例中compute_driver=libvirt.LibvirtDriver因此最终会通过import_object 导入nova.virt.libvirt.LibvirtDriver