QEMU源码全解析 —— virtio（13）

2023-12-17 13:04
文章标签 源码 解析 13 qemu virtio

本文主要是介绍QEMU源码全解析 —— virtio（13），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：

通过前文书（从QEMU源码全解析 —— virtio（9）开始）对整个流程以及各个相关函数的解析，可以看到从virtio PCI代理设备的具现化到virtio设备的具现化过程。但前述分析还遗漏了一部分，就是virtio设备挂载到virtio总线上的行为。这个过程是在virtio_device_realize函数中通过调用virtio_bus_device_plugged函数完成的。在QEMU源码全解析 —— virtio（11）中提到过，有图为证：

virtio_bus_device_plugged函数的作用就是将virtio设备插入到virtio总线上去。其源码在hw/virtio/virtio-bus.c中，如下：

/* A VirtIODevice is being plugged */
void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp)
{DeviceState *qdev = DEVICE(vdev);BusState *qbus = BUS(qdev_get_parent_bus(qdev));VirtioBusState *bus = VIRTIO_BUS(qbus);VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus);VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);bool has_iommu = virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);bool vdev_has_iommu;Error *local_err = NULL;DPRINTF("%s: plug device.\n", qbus->name);if (klass->pre_plugged != NULL) {klass->pre_plugged(qbus->parent, &local_err);if (local_err) {error_propagate(errp, local_err);return;}}/* Get the features of the plugged device. */assert(vdc->get_features != NULL);vdev->host_features = vdc->get_features(vdev, vdev->host_features,&local_err);if (local_err) {error_propagate(errp, local_err);return;}if (klass->device_plugged != NULL) {klass->device_plugged(qbus->parent, &local_err);}if (local_err) {error_propagate(errp, local_err);return;}vdev->dma_as = &address_space_memory;if (has_iommu) {vdev_has_iommu = virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);/** Present IOMMU_PLATFORM to the driver iff iommu_plattform=on and* device operational. If the driver does not accept IOMMU_PLATFORM* we fail the device.*/virtio_add_feature(&vdev->host_features, VIRTIO_F_IOMMU_PLATFORM);if (klass->get_dma_as) {vdev->dma_as = klass->get_dma_as(qbus->parent);if (!vdev_has_iommu && vdev->dma_as != &address_space_memory) {error_setg(errp,"iommu_platform=true is not supported by the device");return;}}}
}

virtio_bus_device_plugged函数主要是调用了VirtioBusClass类型的device_plugged回调函数。代码片段如下：

    VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus);……if (klass->device_plugged != NULL) {klass->device_plugged(qbus->parent, &local_err);}if (local_err) {error_propagate(errp, local_err);return;}

device_pluggeg回调函数也即klass->device_plugged函数指针所指向的函数在virtio_pci_bus_class_init函数中被初始化成了virtio_pci_device_plugged函数。virtio_pci_bus_class_init函数在hw/virtio/virtio-pci.c中，代码如下：

static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
{BusClass *bus_class = BUS_CLASS(klass);VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);bus_class->max_dev = 1;k->notify = virtio_pci_notify;k->save_config = virtio_pci_save_config;k->load_config = virtio_pci_load_config;k->save_queue = virtio_pci_save_queue;k->load_queue = virtio_pci_load_queue;k->save_extra_state = virtio_pci_save_extra_state;k->load_extra_state = virtio_pci_load_extra_state;k->has_extra_state = virtio_pci_has_extra_state;k->query_guest_notifiers = virtio_pci_query_guest_notifiers;k->set_guest_notifiers = virtio_pci_set_guest_notifiers;k->set_host_notifier_mr = virtio_pci_set_host_notifier_mr;k->vmstate_change = virtio_pci_vmstate_change;k->pre_plugged = virtio_pci_pre_plugged;k->device_plugged = virtio_pci_device_plugged;k->device_unplugged = virtio_pci_device_unplugged;k->query_nvectors = virtio_pci_query_nvectors;k->ioeventfd_enabled = virtio_pci_ioeventfd_enabled;k->ioeventfd_assign = virtio_pci_ioeventfd_assign;k->get_dma_as = virtio_pci_get_dma_as;k->iommu_enabled = virtio_pci_iommu_enabled;k->queue_enabled = virtio_pci_queue_enabled;
}

virtio_pci_device_plugged函数在hw/virtio/virtio-pci.c中，代码如下：

/* This is called by virtio-bus just after the device is plugged. */
static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
{VirtIOPCIProxy *proxy = VIRTIO_PCI(d);VirtioBusState *bus = &proxy->bus;bool legacy = virtio_pci_legacy(proxy);bool modern;bool modern_pio = proxy->flags & VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY;uint8_t *config;uint32_t size;VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);/** Virtio capabilities present without* VIRTIO_F_VERSION_1 confuses guests*/if (!proxy->ignore_backend_features &&!virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) {virtio_pci_disable_modern(proxy);if (!legacy) {error_setg(errp, "Device doesn't support modern mode, and legacy"" mode is disabled");error_append_hint(errp, "Set disable-legacy to off\n");return;}}modern = virtio_pci_modern(proxy);config = proxy->pci_dev.config;if (proxy->class_code) {pci_config_set_class(config, proxy->class_code);}if (legacy) {if (!virtio_legacy_allowed(vdev)) {/** To avoid migration issues, we allow legacy mode when legacy* check is disabled in the old machine types (< 5.1).*/if (virtio_legacy_check_disabled(vdev)) {warn_report("device is modern-only, but for backward ""compatibility legacy is allowed");} else {error_setg(errp,"device is modern-only, use disable-legacy=on");return;}}if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {error_setg(errp, "VIRTIO_F_IOMMU_PLATFORM was supported by"" neither legacy nor transitional device");return;}/** Legacy and transitional devices use specific subsystem IDs.* Note that the subsystem vendor ID (config + PCI_SUBSYSTEM_VENDOR_ID)* is set to PCI_SUBVENDOR_ID_REDHAT_QUMRANET by default.*/pci_set_word(config + PCI_SUBSYSTEM_ID, virtio_bus_get_vdev_id(bus));if (proxy->trans_devid) {pci_config_set_device_id(config, proxy->trans_devid);}} else {/* pure virtio-1.0 */pci_set_word(config + PCI_VENDOR_ID,PCI_VENDOR_ID_REDHAT_QUMRANET);pci_set_word(config + PCI_DEVICE_ID,PCI_DEVICE_ID_VIRTIO_10_BASE + virtio_bus_get_vdev_id(bus));pci_config_set_revision(config, 1);}config[PCI_INTERRUPT_PIN] = 1;if (modern) {struct virtio_pci_cap cap = {.cap_len = sizeof cap,};struct virtio_pci_notify_cap notify = {.cap.cap_len = sizeof notify,.notify_off_multiplier =cpu_to_le32(virtio_pci_queue_mem_mult(proxy)),};struct virtio_pci_cfg_cap cfg = {.cap.cap_len = sizeof cfg,.cap.cfg_type = VIRTIO_PCI_CAP_PCI_CFG,};struct virtio_pci_notify_cap notify_pio = {.cap.cap_len = sizeof notify,.notify_off_multiplier = cpu_to_le32(0x0),};struct virtio_pci_cfg_cap *cfg_mask;virtio_pci_modern_regions_init(proxy, vdev->name);virtio_pci_modern_mem_region_map(proxy, &proxy->common, &cap);virtio_pci_modern_mem_region_map(proxy, &proxy->isr, &cap);virtio_pci_modern_mem_region_map(proxy, &proxy->device, &cap);virtio_pci_modern_mem_region_map(proxy, &proxy->notify, &notify.cap);if (modern_pio) {memory_region_init(&proxy->io_bar, OBJECT(proxy),"virtio-pci-io", 0x4);pci_register_bar(&proxy->pci_dev, proxy->modern_io_bar_idx,PCI_BASE_ADDRESS_SPACE_IO, &proxy->io_bar);virtio_pci_modern_io_region_map(proxy, &proxy->notify_pio,&notify_pio.cap);}pci_register_bar(&proxy->pci_dev, proxy->modern_mem_bar_idx,PCI_BASE_ADDRESS_SPACE_MEMORY |PCI_BASE_ADDRESS_MEM_PREFETCH |PCI_BASE_ADDRESS_MEM_TYPE_64,&proxy->modern_bar);proxy->config_cap = virtio_pci_add_mem_cap(proxy, &cfg.cap);cfg_mask = (void *)(proxy->pci_dev.wmask + proxy->config_cap);pci_set_byte(&cfg_mask->cap.bar, ~0x0);pci_set_long((uint8_t *)&cfg_mask->cap.offset, ~0x0);pci_set_long((uint8_t *)&cfg_mask->cap.length, ~0x0);pci_set_long(cfg_mask->pci_cfg_data, ~0x0);}if (proxy->nvectors) {int err = msix_init_exclusive_bar(&proxy->pci_dev, proxy->nvectors,proxy->msix_bar_idx, NULL);if (err) {/* Notice when a system that supports MSIx can't initialize it */if (err != -ENOTSUP) {warn_report("unable to init msix vectors to %" PRIu32,proxy->nvectors);}proxy->nvectors = 0;}}proxy->pci_dev.config_write = virtio_write_config;proxy->pci_dev.config_read = virtio_read_config;if (legacy) {size = VIRTIO_PCI_REGION_SIZE(&proxy->pci_dev)+ virtio_bus_get_vdev_config_len(bus);size = pow2ceil(size);memory_region_init_io(&proxy->bar, OBJECT(proxy),&virtio_pci_config_ops,proxy, "virtio-pci", size);pci_register_bar(&proxy->pci_dev, proxy->legacy_io_bar_idx,PCI_BASE_ADDRESS_SPACE_IO, &proxy->bar);}
}

可以看到，virtio_pci_device_plugged函数比较长，在笔者选用的qemu-8.1.3版本的源码中有160行左右。

对于virtio_pci_device_plugged函数的详细解析，请看下回。

这篇关于QEMU源码全解析 —— virtio（13）的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！


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