QEMU源码全解析 —— PCI设备模拟（3）

已于 2024-10-11 08:02:18 修改
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分类专栏： QEMU/KVM KVM 文章标签： QEMU KVM PCI
于 2024-01-11 20:59:31 首次发布
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本文继续上篇，深入解析QEMU如何模拟PCI设备。主要讨论pci_qdev_realize函数的第二部分，包括调用PCI设备类的realize函数，并逐步剖析DECLARE_OBJ_CHECKERS、PCI_DEVICE_GET_CLASS等相关宏的实现细节。
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接前一篇文章：

2. PCI 设备的模拟

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： 

  1. static const TypeInfo pci_device_type_info = {
  2.     .name = TYPE_PCI_DEVICE,
  3.     .parent = TYPE_DEVICE,
  4.     .instance_size = sizeof(PCIDevice),
  5.     .abstract = true,
  6.     .class_size = sizeof(PCIDeviceClass),
  7.     .class_init = pci_device_class_init,
  8.     .class_base_init = pci_device_class_base_init,
  9. };
  10.  
  11. static void pci_register_types(void)
  12. {
  13.     type_register_static(&pci_bus_info);
  14.     type_register_static(&pcie_bus_info);
  15.     type_register_static(&cxl_bus_info);
  16.     type_register_static(&conventional_pci_interface_info);
  17.     type_register_static(&cxl_interface_info);
  18.     type_register_static(&pcie_interface_info);
  19.     type_register_static(&pci_device_type_info);
  20. }
  21.  
  22. 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。为了便于理解和回顾，再次贴出该函数源码，在hw/pci/pci.c中，如下： 

  1. static void pci_qdev_realize(DeviceState *qdev, Error **errp)
  2. {
  3.     PCIDevice *pci_dev = (PCIDevice *)qdev;
  4.     PCIDeviceClass *pc = PCI_DEVICE_GET_CLASS(pci_dev);
  5.     ObjectClass *klass = OBJECT_CLASS(pc);
  6.     Error *local_err = NULL;
  7.     bool is_default_rom;
  8.     uint16_t class_id;
  9.  
  10.     /*
  11.      * capped by systemd (see: udev-builtin-net_id.c)
  12.      * as it's the only known user honor it to avoid users
  13.      * misconfigure QEMU and then wonder why acpi-index doesn't work
  14.      */
  15.     if (pci_dev->acpi_index > ONBOARD_INDEX_MAX) {
  16.         error_setg(errp, "acpi-index should be less or equal to %u",
  17.                    ONBOARD_INDEX_MAX);
  18.         return;
  19.     }
  20.  
  21.     /*
  22.      * make sure that acpi-index is unique across all present PCI devices
  23.      */
  24.     if (pci_dev->acpi_index) {
  25.         GSequence *used_indexes = pci_acpi_index_list();
  26.  
  27.         if (g_sequence_lookup(used_indexes,
  28.                               GINT_TO_POINTER(pci_dev->acpi_index),
  29.                               g_cmp_uint32, NULL)) {
  30.             error_setg(errp, "a PCI device with acpi-index = %" PRIu32
  31.                        " already exist", pci_dev->acpi_index);
  32.             return;
  33.         }
  34.         g_sequence_insert_sorted(used_indexes,
  35.                                  GINT_TO_POINTER(pci_dev->acpi_index),
  36.                                  g_cmp_uint32, NULL);
  37.     }
  38.  
  39.     if (pci_dev->romsize != -1 && !is_power_of_2(pci_dev->romsize)) {
  40.         error_setg(errp, "ROM size %u is not a power of two", pci_dev->romsize);
  41.         return;
  42.     }
  43.  
  44.     /* initialize cap_present for pci_is_express() and pci_config_size(),
  45.      * Note that hybrid PCIs are not set automatically and need to manage
  46.      * QEMU_PCI_CAP_EXPRESS manually */
  47.     if (object_class_dynamic_cast(klass, INTERFACE_PCIE_DEVICE) &&
  48.        !object_class_dynamic_cast(klass, INTERFACE_CONVENTIONAL_PCI_DEVICE)) {
  49.         pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;
  50.     }
  51.  
  52.     if (object_class_dynamic_cast(klass, INTERFACE_CXL_DEVICE)) {
  53.         pci_dev->cap_present |= QEMU_PCIE_CAP_CXL;
  54.     }
  55.  
  56.     pci_dev = do_pci_register_device(pci_dev,
  57.                                      object_get_typename(OBJECT(qdev)),
  58.                                      pci_dev->devfn, errp);
  59.     if (pci_dev == NULL)
  60.         return;
  61.  
  62.     if (pc->realize) {
  63.         pc->realize(pci_dev, &local_err);
  64.         if (local_err) {
  65.             error_propagate(errp, local_err);
  66.             do_pci_unregister_device(pci_dev);
  67.             return;
  68.         }
  69.     }
  70.  
  71.     /*
  72.      * A PCIe Downstream Port that do not have ARI Forwarding enabled must
  73.      * associate only Device 0 with the device attached to the bus
  74.      * representing the Link from the Port (PCIe base spec rev 4.0 ver 0.3,
  75.      * sec 7.3.1).
  76.      * With ARI, PCI_SLOT() can return non-zero value as the traditional
  77.      * 5-bit Device Number and 3-bit Function Number fields in its associated
  78.      * Routing IDs, Requester IDs and Completer IDs are interpreted as a
  79.      * single 8-bit Function Number. Hence, ignore ARI capable devices.
  80.      */
  81.     if (pci_is_express(pci_dev) &&
  82.         !pcie_find_capability(pci_dev, PCI_EXT_CAP_ID_ARI) &&
  83.         pcie_has_upstream_port(pci_dev) &&
  84.         PCI_SLOT(pci_dev->devfn)) {
  85.         warn_report("PCI: slot %d is not valid for %s,"
  86.                     " parent device only allows plugging into slot 0.",
  87.                     PCI_SLOT(pci_dev->devfn), pci_dev->name);
  88.     }
  89.  
  90.     if (pci_dev->failover_pair_id) {
  91.         if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
  92.             error_setg(errp, "failover primary device must be on "
  93.                              "PCIExpress bus");
  94.             pci_qdev_unrealize(DEVICE(pci_dev));
  95.             return;
  96.         }
  97.         class_id = pci_get_word(pci_dev->config + PCI_CLASS_DEVICE);
  98.         if (class_id != PCI_CLASS_NETWORK_ETHERNET) {
  99.             error_setg(errp, "failover primary device is not an "
  100.                              "Ethernet device");
  101.             pci_qdev_unrealize(DEVICE(pci_dev));
  102.             return;
  103.         }
  104.         if ((pci_dev->cap_present & QEMU_PCI_CAP_MULTIFUNCTION)
  105.             || (PCI_FUNC(pci_dev->devfn) != 0)) {
  106.             error_setg(errp, "failover: primary device must be in its own "
  107.                               "PCI slot");
  108.             pci_qdev_unrealize(DEVICE(pci_dev));
  109.             return;
  110.         }
  111.         qdev->allow_unplug_during_migration = true;
  112.     }
  113.  
  114.     /* rom loading */
  115.     is_default_rom = false;
  116.     if (pci_dev->romfile == NULL && pc->romfile != NULL) {
  117.         pci_dev->romfile = g_strdup(pc->romfile);
  118.         is_default_rom = true;
  119.     }
  120.  
  121.     pci_add_option_rom(pci_dev, is_default_rom, &local_err);
  122.     if (local_err) {
  123.         error_propagate(errp, local_err);
  124.         pci_qdev_unrealize(DEVICE(pci_dev));
  125.         return;
  126.     }
  127.  
  128.     pci_set_power(pci_dev, true);
  129.  
  130.     pci_dev->msi_trigger = pci_msi_trigger;
  131. }

（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： 

  1.     if (pc->realize) {
  2.         pc->realize(pci_dev, &local_err);
  3.         if (local_err) {
  4.             error_propagate(errp, local_err);
  5.             do_pci_unregister_device(pci_dev);
  6.             return;
  7.         }
  8.     }

pc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： 

  1. #define TYPE_PCI_DEVICE "pci-device"
  2. typedef struct PCIDeviceClass PCIDeviceClass;
  3. DECLARE_OBJ_CHECKERS(PCIDevice, PCIDeviceClass,
  4.                      PCI_DEVICE, TYPE_PCI_DEVICE)

而struct PCIDeviceClass的定义也在include/hw/pci/pci_device.h中，代码如下： 

  1. struct PCIDeviceClass {
  2.     DeviceClass parent_class;
  3.  
  4.     void (*realize)(PCIDevice *dev, Error **errp);
  5.     PCIUnregisterFunc *exit;
  6.     PCIConfigReadFunc *config_read;
  7.     PCIConfigWriteFunc *config_write;
  8.  
  9.     uint16_t vendor_id;
  10.     uint16_t device_id;
  11.     uint8_t revision;
  12.     uint16_t class_id;
  13.     uint16_t subsystem_vendor_id;       /* only for header type = 0 */
  14.     uint16_t subsystem_id;              /* only for header type = 0 */
  15.  
  16.     const char *romfile;                /* rom bar */
  17. };

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源码中搜索却也并没有搜到。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： 

  1. #define TYPE_PCI_DEVICE "pci-device"
  2. typedef struct PCIDeviceClass PCIDeviceClass;
  3. DECLARE_OBJ_CHECKERS(PCIDevice, PCIDeviceClass,
  4.                      PCI_DEVICE, TYPE_PCI_DEVICE)

DECLARE_OBJ_CHECKERS的定义在include/qom/object.h中，代码如下： 

  1. /**
  2.  * DECLARE_OBJ_CHECKERS:
  3.  * @InstanceType: instance struct name
  4.  * @ClassType: class struct name
  5.  * @OBJ_NAME: the object name in uppercase with underscore separators
  6.  * @TYPENAME: type name
  7.  *
  8.  * Direct usage of this macro should be avoided, and the complete
  9.  * OBJECT_DECLARE_TYPE macro is recommended instead.
  10.  *
  11.  * This macro will provide the three standard type cast functions for a
  12.  * QOM type.
  13.  */
  14. #define DECLARE_OBJ_CHECKERS(InstanceType, ClassType, OBJ_NAME, TYPENAME) \
  15.     DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
  16.     \
  17.     DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME)

代入实际值并展开，得到： 

  1.     DECLARE_INSTANCE_CHECKER(PCIDevice, PCI_DEVICE, TYPE_PCI_DEVICE)
  2.     
  3.     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： 

  1. /**
  2.  * DECLARE_INSTANCE_CHECKER:
  3.  * @InstanceType: instance struct name
  4.  * @OBJ_NAME: the object name in uppercase with underscore separators
  5.  * @TYPENAME: type name
  6.  *
  7.  * Direct usage of this macro should be avoided, and the complete
  8.  * OBJECT_DECLARE_TYPE macro is recommended instead.
  9.  *
  10.  * This macro will provide the instance type cast functions for a
  11.  * QOM type.
  12.  */
  13. #define DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
  14.     static inline G_GNUC_UNUSED InstanceType * \
  15.     OBJ_NAME(const void *obj) \
  16.     { return OBJECT_CHECK(InstanceType, obj, TYPENAME); }

代入实际值并展开得： 

  1. static inline G_GNUC_UNUSED PCIDevice* PCI_DEVICE(const void *obj)
  2. {
  3.     return OBJECT_CHECK(PCIDevice, obj, TYPE_PCI_DEVICE);
  4. }

DECLARE_CLASS_CHECKERS宏定义也在include/qom/object.h中，代码如下： 

  1. /**
  2.  * DECLARE_CLASS_CHECKERS:
  3.  * @ClassType: class struct name
  4.  * @OBJ_NAME: the object name in uppercase with underscore separators
  5.  * @TYPENAME: type name
  6.  *
  7.  * Direct usage of this macro should be avoided, and the complete
  8.  * OBJECT_DECLARE_TYPE macro is recommended instead.
  9.  *
  10.  * This macro will provide the class type cast functions for a
  11.  * QOM type.
  12.  */
  13. #define DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME) \
  14.     static inline G_GNUC_UNUSED ClassType * \
  15.     OBJ_NAME##_GET_CLASS(const void *obj) \
  16.     { return OBJECT_GET_CLASS(ClassType, obj, TYPENAME); } \
  17.     \
  18.     static inline G_GNUC_UNUSED ClassType * \
  19.     OBJ_NAME##_CLASS(const void *klass) \
  20.     { return OBJECT_CLASS_CHECK(ClassType, klass, TYPENAME); }

代入实际值并展开得： 

  1. static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_GET_CLASS(const void *obj)
  2. {
  3.     return OBJECT_GET_CLASS(PCIDeviceClass, obj, TYPE_PCI_DEVICE);
  4. }
  5.  
  6. static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_CLASS(const void *klass)
  7. {
  8.     return OBJECT_CLASS_CHECK(PCIDeviceClass, klass, TYPE_PCI_DEVICE);
  9. }

综合两式，最终得到： 

  1. static inline G_GNUC_UNUSED PCIDevice* PCI_DEVICE(const void *obj)
  2. {
  3.     return OBJECT_CHECK(PCIDevice, obj, TYPE_PCI_DEVICE);
  4. }
  5.  
  6. static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_GET_CLASS(const void *obj)
  7. {
  8.     return OBJECT_GET_CLASS(PCIDeviceClass, obj, TYPE_PCI_DEVICE);
  9. }
  10.  
  11. static inline G_GNUC_UNUSED PCIDeviceClass* PCI_DEVICE_CLASS(const void *klass)
  12. {
  13.     return OBJECT_CLASS_CHECK(PCIDeviceClass, klass, TYPE_PCI_DEVICE);
  14. }

这样，最终就得到了也可以说生成出了PCI_DEVICE_GET_CLASS。

再深入跟进一点，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： 

  1. /**
  2.  * OBJECT_CHECK:
  3.  * @type: The C type to use for the return value.
  4.  * @obj: A derivative of @type to cast.
  5.  * @name: The QOM typename of @type
  6.  *
  7.  * A type safe version of @object_dynamic_cast_assert.  Typically each class
  8.  * will define a macro based on this type to perform type safe dynamic_casts to
  9.  * this object type.
  10.  *
  11.  * If an invalid object is passed to this function, a run time assert will be
  12.  * generated.
  13.  */
  14. #define OBJECT_CHECK(type, obj, name) \
  15.     ((type *)object_dynamic_cast_assert(OBJECT(obj), (name), \
  16.                                         __FILE__, __LINE__, __func__))
  17.  
  18. /**
  19.  * OBJECT_CLASS_CHECK:
  20.  * @class_type: The C type to use for the return value.
  21.  * @class: A derivative class of @class_type to cast.
  22.  * @name: the QOM typename of @class_type.
  23.  *
  24.  * A type safe version of @object_class_dynamic_cast_assert.  This macro is
  25.  * typically wrapped by each type to perform type safe casts of a class to a
  26.  * specific class type.
  27.  */
  28. #define OBJECT_CLASS_CHECK(class_type, class, name) \
  29.     ((class_type *)object_class_dynamic_cast_assert(OBJECT_CLASS(class), (name), \
  30.                                                __FILE__, __LINE__, __func__))
  31.  
  32. /**
  33.  * OBJECT_GET_CLASS:
  34.  * @class: The C type to use for the return value.
  35.  * @obj: The object to obtain the class for.
  36.  * @name: The QOM typename of @obj.
  37.  *
  38.  * This function will return a specific class for a given object.  Its generally
  39.  * used by each type to provide a type safe macro to get a specific class type
  40.  * from an object.
  41.  */
  42. #define OBJECT_GET_CLASS(class, obj, name) \
  43.     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。

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