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使用guestfs 可以在不用mount的情况下直接处理虚拟机的镜像文件，而使用localfs的话就需要将虚拟机的镜像文件mount到host中才能编辑镜像文件.localfs的实现路径为E:\nova\nova\virt\disk\vfs\localfs.pyclass VFSLocalFS(vfs.VFS):    def __init__(self, image, partition=None, imgdir=None):        """Create a new local VFS instance        :param image: instance of nova.virt.image.model.Image        :param partition: the partition number of access        :param imgdir: the directory to mount the image at        """        super(VFSLocalFS, self).__init__(image, partition)		#从其__init__函数可以看出会指定要mount的路径imgdir.        self.imgdir = imgdir        self.mount = None    def setup(self, mount=True):        self.imgdir = tempfile.mkdtemp(prefix="openstack-vfs-localfs")        try:			#将虚拟机镜像文件mount到host中            mnt = mount_api.Mount.instance_for_format(self.image,                                                      self.imgdir,            #默认mount 为true                                         self.partition)            if mount:				#检查是否mount成功                if not mnt.do_mount():                    raise exception.NovaException(mnt.error)			#保存mount结果            self.mount = mnt        except Exception as e:            with excutils.save_and_reraise_exception():                LOG.debug("Failed to mount image: %(ex)s", {'ex': e})                self.teardown() def get_image_fs(self):		#这样在使用的时候，会先调用get_image_fs得到已经mount到host的路径，然后就可以直接编辑镜像文件了.		        if self.mount.device or self.mount.get_dev():            out, err = nova.privsep.fs.get_filesystem_type(self.mount.device)            return out.strip()        return ""

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