接前一篇文章：
QEMU模拟的设备很多都是PCI设备，本节介绍PCI设备的模拟。与所有设备类似，PCI设备的父设备也是TYPE_DEVICE，其定义在QEMU源码根目录/hw/pci/pci.c中，代码如下：
static const TypeInfo pci_device_type_info = {
.name = TYPE_PCI_DEVICE,
.parent = TYPE_DEVICE,
.instance_size = sizeof(PCIDevice),
.abstract = true,
.class_size = sizeof(PCIDeviceClass),
.class_init = pci_device_class_init,
.class_base_init = pci_device_class_base_init,
};
static void pci_register_types(void)
{
type_register_static(&pci_bus_info);
type_register_static(&pcie_bus_info);
type_register_static(&cxl_bus_info);
type_register_static(&conventional_pci_interface_info);
type_register_static(&cxl_interface_info);
type_register_static(&pcie_interface_info);
type_register_static(&pci_device_type_info);
}
type_init(pci_register_types)上一回讲到了PCI设备的具现化函数pci_qdev_realize()，讲解了pci_qdev_realize函数所完成的三个任务中的第一个，本回接着往下讲。为了便于理解，再次贴出该函数源码，在hw/pci/pci.c中，如下：
static void pci_qdev_realize(DeviceState *qdev, Error **errp)
{
PCIDevice *pci_dev = (PCIDevice *)qdev;
PCIDeviceClass *pc = PCI_DEVICE_GET_CLASS(pci_dev);
ObjectClass *klass = OBJECT_CLASS(pc);
Error *local_err = NULL;
bool is_default_rom;
uint16_t class_id;
/*
* capped by systemd (see: udev-builtin-net_id.c)
* as it's the only known user honor it to avoid users
* misconfigure QEMU and then wonder why acpi-index doesn't work
*/
if (pci_dev->acpi_index > ONBOARD_INDEX_MAX) {
error_setg(errp, "acpi-index should be less or equal to %u",
ONBOARD_INDEX_MAX);
return;
}
/*
* make sure that acpi-index is unique across all present PCI devices
*/
if (pci_dev->acpi_index) {
GSequence *used_indexes = pci_acpi_index_list();
if (g_sequence_lookup(used_indexes,
GINT_TO_POINTER(pci_dev->acpi_index),
g_cmp_uint32, NULL)) {
error_setg(errp, "a PCI device with acpi-index = %" PRIu32
" already exist", pci_dev->acpi_index);
return;
}
g_sequence_insert_sorted(used_indexes,
GINT_TO_POINTER(pci_dev->acpi_index),
g_cmp_uint32, NULL);
}
if (pci_dev->romsize != -1 && !is_power_of_2(pci_dev->romsize)) {
error_setg(errp, "ROM size %u is not a power of two", pci_dev->romsize);
return;
}
/* initialize cap_present for pci_is_express() and pci_config_size(),
* Note that hybrid PCIs are not set automatically and need to manage
* QEMU_PCI_CAP_EXPRESS manually */
if (object_class_dynamic_cast(klass, INTERFACE_PCIE_DEVICE) &&
!object_class_dynamic_cast(klass, INTERFACE_CONVENTIONAL_PCI_DEVICE)) {
pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;
}
if (object_class_dynamic_cast(klass, INTERFACE_CXL_DEVICE)) {
pci_dev->cap_present |= QEMU_PCIE_CAP_CXL;
}
pci_dev = do_pci_register_device(pci_dev,
object_get_typename(OBJECT(qdev)),
pci_dev->devfn, errp);
if (pci_dev == NULL)
return;
if (pc->realize) {
pc->realize(pci_dev, &local_err);
if (local_err) {
error_propagate(errp, local_err);
do_pci_unregister_device(pci_dev);
return;
}
}
/*
* A PCIe Downstream Port that do not have ARI Forwarding enabled must
* associate only Device 0 with the device attached to the bus
* representing the Link from the Port (PCIe base spec rev 4.0 ver 0.3,
* sec 7.3.1).
* With ARI, PCI_SLOT() can return non-zero value as the traditional
* 5-bit Device Number and 3-bit Function Number fields in its associated
* Routing IDs, Requester IDs and Completer IDs are interpreted as a
* single 8-bit Function Number. Hence, ignore ARI capable devices.
*/
if (pci_is_express(pci_dev) &&
!pcie_find_capability(pci_dev, PCI_EXT_CAP_ID_ARI) &&
pcie_has_upstream_port(pci_dev) &&
PCI_SLOT(pci_dev->devfn)) {
warn_report("PCI: slot %d is not valid for %s,"
" parent device only allows plugging into slot 0.",
PCI_SLOT(pci_dev->devfn), pci_dev->name);
}
if (pci_dev->failover_pair_id) {
if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
error_setg(errp, "failover primary device must be on "
"PCIExpress bus");
pci_qdev_unrealize(DEVICE(pci_dev));
return;
}
class_id = pci_get_word(pci_dev->config + PCI_CLASS_DEVICE);
if (class_id != PCI_CLASS_NETWORK_ETHERNET) {
error_setg(errp, "failover primary device is not an "
"Ethernet device");
pci_qdev_unrealize(DEVICE(pci_dev));
return;
}
if ((pci_dev->cap_present & QEMU_PCI_CAP_MULTIFUNCTION)
|| (PCI_FUNC(pci_dev->devfn) != 0)) {
error_setg(errp, "failover: primary device must be in its own "
"PCI slot");
pci_qdev_unrealize(DEVICE(pci_dev));
return;
}
qdev->allow_unplug_during_migration = true;
}
/* rom loading */
is_default_rom = false;
if (pci_dev->romfile == NULL && pc->romfile != NULL) {
pci_dev->romfile = g_strdup(pc->romfile);
is_default_rom = true;
}
pci_add_option_rom(pci_dev, is_default_rom, &local_err);
if (local_err) {
error_propagate(errp, local_err);
pci_qdev_unrealize(DEVICE(pci_dev));
return;
}
pci_set_power(pci_dev, true);
pci_dev->msi_trigger = pci_msi_trigger;
}（2）其次，pci_qdev_realize函数调用PCI设备所属的class的realize函数，即pc->realize函数。
代码片段如下：
if (pc->realize) {
pc->realize(pci_dev, &local_err);
if (local_err) {
error_propagate(errp, local_err);
do_pci_unregister_device(pci_dev);
return;
}
}pc的是PCIDeviceClass结构类型的指针，PCIDeviceClass的定义在include/hw/pci/pci_device.h中，代码如下：
#define TYPE_PCI_DEVICE "pci-device"
typedef struct PCIDeviceClass PCIDeviceClass;
DECLARE_OBJ_CHECKERS(PCIDevice, PCIDeviceClass,
PCI_DEVICE, TYPE_PCI_DEVICE)
而struct PCIDeviceClass的定义也在include/hw/pci/pci_device.h中，代码如下：
struct PCIDeviceClass {
DeviceClass parent_class;
void (*realize)(PCIDevice *dev, Error **errp);
PCIUnregisterFunc *exit;
PCIConfigReadFunc *config_read;
PCIConfigWriteFunc *config_write;
uint16_t vendor_id;
uint16_t device_id;
uint8_t revision;
uint16_t class_id;
uint16_t subsystem_vendor_id; /* only for header type = 0 */
uint16_t subsystem_id; /* only for header type = 0 */
const char *romfile; /* rom bar */
};PCI_DEVICE_GET_CLASS是一个宏定义，但是在QEMU源码中搜素怎么都搜不到。笔者开始以为是在Linux内核源码中的定义，后来在Linux源码中搜索却并未搜到。后来几经周折，终于弄清楚了其具体细节。
要弄清楚PCI_DEVICE_GET_CLASS，得先从DECLARE_OBJ_CHECKERS讲起。DECLARE_OBJ_CHECKERS的相关代码在include/hw/pci/pci_device.h中：
#define TYPE_PCI_DEVICE "pci-device"
typedef struct PCIDeviceClass PCIDeviceClass;
DECLARE_OBJ_CHECKERS(PCIDevice, PCIDeviceClass,
PCI_DEVICE, TYPE_PCI_DEVICE)
DECLARE_OBJ_CHECKERS的定义在include/qom/object.h中，代码如下：
/**
* DECLARE_OBJ_CHECKERS:
* @InstanceType: instance struct name
* @ClassType: class struct name
* @OBJ_NAME: the object name in uppercase with underscore separators
* @TYPENAME: type name
*
* Direct usage of this macro should be avoided, and the complete
* OBJECT_DECLARE_TYPE macro is recommended instead.
*
* This macro will provide the three standard type cast functions for a
* QOM type.
*/
#define DECLARE_OBJ_CHECKERS(InstanceType, ClassType, OBJ_NAME, TYPENAME) \
DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
\
DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME)代入实际值并展开，得到：
DECLARE_INSTANCE_CHECKER(PCIDevice, PCI_DEVICE, TYPE_PCI_DEVICE)
DECLARE_CLASS_CHECKERS(PCIDeviceClass, PCI_DEVICE, TYPE_PCI_DEVICE)DECLARE_INSTANCE_CHECKER宏定义也在include/qom/object.h中，代码如下：
/**
* DECLARE_INSTANCE_CHECKER:
* @InstanceType: instance struct name
* @OBJ_NAME: the object name in uppercase with underscore separators
* @TYPENAME: type name
*
* Direct usage of this macro should be avoided, and the complete
* OBJECT_DECLARE_TYPE macro is recommended instead.
*
* This macro will provide the instance type cast functions for a
* QOM type.
*/
#define DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
static inline G_GNUC_UNUSED InstanceType * \
OBJ_NAME(const void *obj) \
{ return OBJECT_CHECK(InstanceType, obj, TYPENAME); }代入实际值并展开得：
static inline G_GNUC_UNUSED PCIDevice* PCI_DEVICE(const void *obj)
{
return OBJECT_CHECK(PCIDevice, obj, TYPE_PCI_DEVICE);
}DECLARE_CLASS_CHECKERS宏定义也在include/qom/object.h中，代码如下：
/**
* DECLARE_CLASS_CHECKERS:
* @ClassType: class struct name
* @OBJ_NAME: the object name in uppercase with underscore separators
* @TYPENAME: type name
*
* Direct usage of this macro should be avoided, and the complete
* OBJECT_DECLARE_TYPE macro is recommended instead.
*
* This macro will provide the class type cast functions for a
* QOM type.
*/
#define DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME) \
static inline G_GNUC_UNUSED ClassType * \
OBJ_NAME##_GET_CLASS(const void *obj) \
{ return OBJECT_GET_CLASS(ClassType, obj, TYPENAME); } \
\
static inline G_GNUC_UNUSED ClassType * \
OBJ_NAME##_CLASS(const void *klass) \
{ return OBJECT_CLASS_CHECK(ClassType, klass, TYPENAME); }代入实际值并展开得：
static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_GET_CLASS(const void *obj)
{
return OBJECT_GET_CLASS(PCIDeviceClass, obj, TYPE_PCI_DEVICE);
}
static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_CLASS(const void *klass)
{
return OBJECT_CLASS_CHECK(PCIDeviceClass, klass, TYPE_PCI_DEVICE);
}
综合两式，最终得到：
static inline G_GNUC_UNUSED PCIDevice* PCI_DEVICE(const void *obj)
{
return OBJECT_CHECK(PCIDevice, obj, TYPE_PCI_DEVICE);
}
static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_GET_CLASS(const void *obj)
{
return OBJECT_GET_CLASS(PCIDeviceClass, obj, TYPE_PCI_DEVICE);
}
static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_CLASS(const void *klass)
{
return OBJECT_CLASS_CHECK(PCIDeviceClass, klass, TYPE_PCI_DEVICE);
}
这样，最终就得到了也可以说生成出了PCI_DEVICE_GET_CLASS。
再深入跟紧一点，OBJECT_CHECK、OBJECT_GET_CLASS、OBJECT_CLASS_CHECK三个宏的定义都在include/qom/object.h中，代码如下：
/**
* OBJECT_CHECK:
* @type: The C type to use for the return value.
* @obj: A derivative of @type to cast.
* @name: The QOM typename of @type
*
* A type safe version of @object_dynamic_cast_assert. Typically each class
* will define a macro based on this type to perform type safe dynamic_casts to
* this object type.
*
* If an invalid object is passed to this function, a run time assert will be
* generated.
*/
#define OBJECT_CHECK(type, obj, name) \
((type *)object_dynamic_cast_assert(OBJECT(obj), (name), \
__FILE__, __LINE__, __func__))
/**
* OBJECT_CLASS_CHECK:
* @class_type: The C type to use for the return value.
* @class: A derivative class of @class_type to cast.
* @name: the QOM typename of @class_type.
*
* A type safe version of @object_class_dynamic_cast_assert. This macro is
* typically wrapped by each type to perform type safe casts of a class to a
* specific class type.
*/
#define OBJECT_CLASS_CHECK(class_type, class, name) \
((class_type *)object_class_dynamic_cast_assert(OBJECT_CLASS(class), (name), \
__FILE__, __LINE__, __func__))
/**
* OBJECT_GET_CLASS:
* @class: The C type to use for the return value.
* @obj: The object to obtain the class for.
* @name: The QOM typename of @obj.
*
* This function will return a specific class for a given object. Its generally
* used by each type to provide a type safe macro to get a specific class type
* from an object.
*/
#define OBJECT_GET_CLASS(class, obj, name) \
OBJECT_CLASS_CHECK(class, object_get_class(OBJECT(obj)), name)
至此，pci_qdev_realize函数所做的第二方面工作即所调用的第2个函数也就是PCI设备所属的class的realize函数，即pc->realize函数就解析完了。
欲知后事如何，且看下回分解。