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在openstack中创建虚拟机的底层实现是nova使用了libvirt，代码在nova/virt/libvirt/driver.py。
#image_meta:镜像的相关内容，#injected_files:要注入到VM的文件
#network_info:网络相关信息。block_device_info:磁盘相关信息
def spawn(self, context, instance, image_meta, injected_files,
admin_password, network_info=None, block_device_info=None):
#确定客户机的磁盘映射关系
disk_info = blockinfo.get_disk_info(CONF.libvirt.virt_type,
instance,
block_device_info,
image_meta)
#创建VM的磁盘文件
self._create_image(context, instance,
disk_info['mapping'],
network_info=network_info,
block_device_info=block_device_info,
files=injected_files,
admin_pass=admin_password)
#综合各方面的信息，拼装一个define VM的XML文件
xml = self.to_xml(context, instance, network_info,
disk_info, image_meta,
block_device_info=block_device_info,
write_to_disk=True)
#向neutron请求IP，然后使用xml创建domain
self._create_domain_and_network(context, xml, instance, network_info,
block_device_info)
以下将具体分析上述4个函数，比源码略有删减
#virt_type: cpu_mode,一般为kvm,具体可參见该选项的凝视
def get_disk_info(virt_type, instance, block_device_info=None,
image_meta=None, rescue=False):
#依据device_type和virt_type返回总线类型。如kvm和disk。则会返回virtio
#cdrom和kvm，则会返回ide
disk_bus = get_disk_bus_for_device_type(virt_type, image_meta, "disk")
cdrom_bus = get_disk_bus_for_device_type(virt_type, image_meta, "cdrom")
#确定如何映射默认的disks到VM中，如root挂到/dev/vda等。还有swap, local等
mapping = get_disk_mapping(virt_type, instance,
disk_bus, cdrom_bus,
block_device_info,
image_meta, rescue)
#准备磁盘文件
def _create_image(self, context, instance,
disk_mapping, suffix='',
disk_images=None, network_info=None,
block_device_info=None, files=None,
admin_pass=None, inject_files=True):
#推断是否从volume启动VM
booted_from_volume = self._is_booted_from_volume(
instance, disk_mapping)
#依据images_type。如qcow2, RBD等，创建各种格式的镜像相应的类
def image(fname, image_type=CONF.libvirt.images_type):
return self.image_backend.image(instance,
fname + suffix, image_type)
#创建raw格式的镜像相应的类
def raw(fname):
return image(fname, image_type='raw')
LOG.info(_('Creating image'), instance=instance)
if not disk_images:
disk_images = {'image_id': instance['image_ref'],
'kernel_id': instance['kernel_id'],
'ramdisk_id': instance['ramdisk_id']}
if disk_images['kernel_id']:
fname = imagecache.get_cache_fname(disk_images, 'kernel_id')
#这里用到了上面定义的def raw()。其返回一个raw类型的类。cache()使用#fetch_image()完毕镜像文件的kernel下载，关于镜像的下载具体情况能够參#考：http://blog.csdn.net/epugv/article/details/27970625
raw('kernel').cache(fetch_func=libvirt_utils.fetch_image,
context=context,
filename=fname,
image_id=disk_images['kernel_id'],
user_id=instance['user_id'],
project_id=instance['project_id'])
if disk_images['ramdisk_id']:
fname = imagecache.get_cache_fname(disk_images, 'ramdisk_id')
#完毕ramdisk文件下载
raw('ramdisk').cache(fetch_func=libvirt_utils.fetch_image,
context=context,
filename=fname,
image_id=disk_images['ramdisk_id'],
user_id=instance['user_id'],
project_id=instance['project_id'])
# 创建暂时磁盘，ephemeral disk指的是除了root disk和swap disk之外的ephemeral
#空间
ephemeral_gb = instance['ephemeral_gb']
if 'disk.local' in disk_mapping:
disk_image = image('disk.local')
fn = functools.partial(self._create_ephemeral,
fs_label='ephemeral0',
os_type=instance["os_type"],
is_block_dev=disk_image.is_block_dev)
fname = "ephemeral_%s_%s" % (ephemeral_gb, os_type_with_default)
size = ephemeral_gb * units.Gi
disk_image.cache(fetch_func=fn,
filename=fname,
size=size,
ephemeral_size=ephemeral_gb)
#假设还有ephemeral disk，继续创建。label为'ephemeral%d' % idx
for idx, eph in enumerate(driver.block_device_info_get_ephemerals(
block_device_info)):
disk_image = image(blockinfo.get_eph_disk(idx))
fn = functools.partial(self._create_ephemeral,
fs_label='ephemeral%d' % idx,
os_type=instance["os_type"],
is_block_dev=disk_image.is_block_dev)
size = eph['size'] * units.Gi
fname = "ephemeral_%s_%s" % (eph['size'], os_type_with_default)
disk_image.cache(
fetch_func=fn,
filename=fname,
size=size,
ephemeral_size=eph['size'])
#创建swap disk
if swap_mb > 0:
size = swap_mb * units.Mi
image('disk.swap').cache(fetch_func=self._create_swap,
filename="swap_%s" % swap_mb,
size=size,
swap_mb=swap_mb)
# OpenStack还能够使用Config Drive实现元数据的注入，可是在制作image时一
#定要安装cloud-init软件，否则无法实现元数据注入
# Config drive
if configdrive.required_by(instance):
LOG.info(_('Using config drive'), instance=instance)
extra_md = {}
if admin_pass:
extra_md['admin_pass'] = admin_pass
#提取instance matedata
inst_md = instance_metadata.InstanceMetadata(instance,
content=files, extra_md=extra_md, network_info=network_info)
with configdrive.ConfigDriveBuilder(instance_md=inst_md) as cdb:
configdrive_path = self._get_disk_config_path(instance)
LOG.info(_('Creating config drive at %(path)s'),
{'path': configdrive_path}, instance=instance)
#将metadata写入实例所在的目录下的一个disk.config文件里
try:
cdb.make_drive(configdrive_path)
except processutils.ProcessExecutionError as e:
with excutils.save_and_reraise_exception():
LOG.error(_('Creating config drive failed '
'with error: %s'),
e, instance=instance)
#依据官方文档 -2 => disable, -1 => inspect (libguestfs only), 0 =>
#not partitioned, >0 => partition number
# File injection only if needed
elif inject_files and CONF.libvirt.inject_partition != -2:
if booted_from_volume:
LOG.warn(_('File injection into a boot from volume '
'instance is not supported'), instance=instance)
self._inject_data(
instance, network_info, admin_pass, files, suffix)
def to_xml(self, context, instance, network_info, disk_info,
image_meta=None, rescue=None,
block_device_info=None, write_to_disk=False):
# We should get image metadata every time for generating xml
if image_meta is None:
image_ref = instance['image_ref']
image_meta = compute_utils.get_image_metadata(
context, self._image_api, image_ref, instance)
msg = ('Start to_xml '
'network_info=%(network_info)s '
'disk_info=%(disk_info)s '
'image_meta=%(image_meta)s rescue=%(rescue)s '
'block_device_info=%(block_device_info)s' %
{'network_info': network_info_str, 'disk_info': disk_info,
'image_meta': image_meta, 'rescue': rescue,
'block_device_info': block_device_info})
#返回guest的具体參数
conf = self.get_guest_config(instance, network_info, image_meta,
disk_info, rescue, block_device_info)
xml = conf.to_xml()#将具体參数使用etree.tostring()生产一个xml dom
def _create_domain_and_network(self, context, xml, instance, network_info,
block_device_info=None, power_on=True,
reboot=False, vifs_already_plugged=False):
for vol in block_device_mapping:
connection_info = vol['connection_info']
disk_info = blockinfo.get_info_from_bdm(
CONF.libvirt.virt_type, vol)
#挂载volume前与volume建立连接，如iscsi中的discover
conf = self.volume_driver_method('connect_volume',
connection_info,
disk_info)
#。。。。。。
launch_flags = events and libvirt.VIR_DOMAIN_START_PAUSED or 0
try:
with self.virtapi.wait_for_instance_event(
instance, events, deadline=timeout,
error_callback=self._neutron_failed_callback):
self.plug_vifs(instance, network_info)#向network注入VIF
self.firewall_driver.setup_basic_filtering(instance,
network_info)
self.firewall_driver.prepare_instance_filter(instance,
network_info)
domain = self._create_domain(#调用libvirt的#defineXML () and #createWithFlags()
xml, instance=instance,
launch_flags=launch_flags,
power_on=power_on)
#应用防火墙
self.firewall_driver.apply_instance_filter(instance,
network_info)
#以下是错误处理。不表