本文主要是介绍QEMU源码全解析 —— virtio(5),希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!
接前一篇文章:
本文内容参考:
《趣谈Linux操作系统》 —— 刘超,极客时间
《QEMU/KVM》源码解析与应用 —— 李强,机械工业出版社
特此致谢!
上一回以virtio balloon设备为例概述了具体的virtio设备、virtio PCI代理设备、virtio公共设备的关系,如下图所示:
本回讲解代码细节。
仍以virtio balloon设备为例分析virtio设备的初始化过程。再次贴出之前的相关代码:
- virtio balloon PCI设备
virtio balloon PCI设备的定义在hw/virtio/virtio-balloon-pci.c中,代码如下:
static const VirtioPCIDeviceTypeInfo virtio_balloon_pci_info = {.base_name = TYPE_VIRTIO_BALLOON_PCI,.generic_name = "virtio-balloon-pci",.transitional_name = "virtio-balloon-pci-transitional",.non_transitional_name = "virtio-balloon-pci-non-transitional",.instance_size = sizeof(VirtIOBalloonPCI),.instance_init = virtio_balloon_pci_instance_init,.class_init = virtio_balloon_pci_class_init,
};static void virtio_balloon_pci_register(void)
{virtio_pci_types_register(&virtio_balloon_pci_info);
}type_init(virtio_balloon_pci_register)
- virtual balloon设备
virtual balloon设备的定义在hw/virtio/virtio-balloon.c中,代码如下:
static const TypeInfo virtio_balloon_info = {.name = TYPE_VIRTIO_BALLOON,.parent = TYPE_VIRTIO_DEVICE,.instance_size = sizeof(VirtIOBalloon),.instance_init = virtio_balloon_instance_init,.class_init = virtio_balloon_class_init,
};static void virtio_register_types(void)
{type_register_static(&virtio_balloon_info);
}type_init(virtio_register_types)
创建virtio balloon设备时只需要创建其PCI代理设备(即TYPE_VIRTIO_BALOON_PCI)即可,在命令行指定“-device virtio-balloon-pci”。先来看实例化函数virtio_balloon_pci_instance_init,其在hw/virtio/virtio-balloon-pci.c中(就在virtio_balloon_pci_info的定义上边),代码如下:
static void virtio_balloon_pci_instance_init(Object *obj)
{VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(obj);virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),TYPE_VIRTIO_BALLOON);object_property_add_alias(obj, "guest-stats", OBJECT(&dev->vdev),"guest-stats");object_property_add_alias(obj, "guest-stats-polling-interval",OBJECT(&dev->vdev),"guest-stats-polling-interval");
}
TYPE_VIRTIO_BALLOON_PCI的实例化函数是virtio_balloon_pci_instance_init,在该函数中会调用virtio_instance_init_common,并将VirtIOBalloonPCI结构体的vdev成员地址以及TYPE_VIRTIO_BALLOON作为参数传递给该函数。
virtio_instance_init_common函数在hw/virtio/virtio.c中,代码如下:
void virtio_instance_init_common(Object *proxy_obj, void *data,size_t vdev_size, const char *vdev_name)
{DeviceState *vdev = data;object_initialize_child_with_props(proxy_obj, "virtio-backend", vdev,vdev_size, vdev_name, &error_abort,NULL);qdev_alias_all_properties(vdev, proxy_obj);
}
object_initialize_child_with_props函数在qom/object.c中,代码如下:
bool object_initialize_child_with_props(Object *parentobj,const char *propname,void *childobj, size_t size,const char *type,Error **errp, ...)
{va_list vargs;bool ok;va_start(vargs, errp);ok = object_initialize_child_with_propsv(parentobj, propname,childobj, size, type, errp,vargs);va_end(vargs);return ok;
}
object_initialize_child_with_propsv函数在同文件中(就在下边),代码如下:
bool object_initialize_child_with_propsv(Object *parentobj,const char *propname,void *childobj, size_t size,const char *type,Error **errp, va_list vargs)
{bool ok = false;Object *obj;UserCreatable *uc;object_initialize(childobj, size, type);obj = OBJECT(childobj);if (!object_set_propv(obj, errp, vargs)) {goto out;}object_property_add_child(parentobj, propname, obj);uc = (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);if (uc) {if (!user_creatable_complete(uc, errp)) {object_unparent(obj);goto out;}}ok = true;out:/** We want @obj's reference to be 1 on success, 0 on failure.* On success, it's 2: one taken by object_initialize(), and one* by object_property_add_child().* On failure in object_initialize() or earlier, it's 1.* On failure afterwards, it's also 1: object_unparent() releases* the reference taken by object_property_add_child().*/object_unref(obj);return ok;
}
由代码可知,virtio_instance_init_common函数经过virtio_instance_init_common() -> object_initialize_child_with_props() -> object_initialize_child_with_propsv(),最终会调用object_initialize函数初始化TYPE_VIRTIO_BALLOON的实例对象VirtIOBalloon,并添加一些属性。由此可见,virtio设备在实例创建过程中并没有做很多事情,大部分的工作是在设备的具现化过程中做的。
在本回结束前,仍然要重点看一下object_initialize_child_with_props函数的说明,在include/qom/object.h中,如下:
/*** object_initialize_child_with_props:* @parentobj: The parent object to add a property to* @propname: The name of the property* @childobj: A pointer to the memory to be used for the object.* @size: The maximum size available at @childobj for the object.* @type: The name of the type of the object to instantiate.* @errp: If an error occurs, a pointer to an area to store the error* @...: list of property names and values** This function will initialize an object. The memory for the object should* have already been allocated. The object will then be added as child property* to a parent with object_property_add_child() function. The returned object* has a reference count of 1 (for the "child<...>" property from the parent),* so the object will be finalized automatically when the parent gets removed.** The variadic parameters are a list of pairs of (propname, propvalue)* strings. The propname of %NULL indicates the end of the property list.* If the object implements the user creatable interface, the object will* be marked complete once all the properties have been processed.** Returns: %true on success, %false on failure.*/
bool object_initialize_child_with_props(Object *parentobj,const char *propname,void *childobj, size_t size, const char *type,Error **errp, ...) G_GNUC_NULL_TERMINATED;
object_initialize_child_with_props:
参数:
parentobj:要向其中添加属性的父对象。
propname:属性名称。
childobj:指向要用于对象的内存的指针。
size:childobj参数可用于对象的最大大小。
type:要实例化的对象的类型的名称。
errp:如果发生错误,则是一个指向存储错误的区域的指针。
...:属性名称和值得列表。
此函数将初始化一个对象。应该已经为对象分配了内存。然后,该对象将作为子属性添加到具有object_property_add_child()函数的父对象中。返回的对象的引用计数为1(对于父对象的“child<…>”属性),因此,当父对象被移除时,该对象将自动完成。
可变参数是一对(propname,propvalue)字符串的列表。属性名为NULL则表示属性列表的末尾。如果该对象实现了用户可创建的接口,则在处理完所有属性后,该对象将被标记为完成。
返回值:
成功时为true,失败时为false。
预知后事如何,且看下回分解。
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