QEMU源码全解析 —— virtio(20)

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接前一篇文章:

上回书重点解析了virtio_pci_modern_probe函数。再来回顾一下其中相关的数据结构:

  • struct virtio_pci_device

struct virtio_pci_device的定义在Linux内核源码/drivers/virtio/virtio_pci_common.h中,如下:

/* Our device structure */
struct virtio_pci_device {
	struct virtio_device vdev;
	struct pci_dev *pci_dev;
	union {
		struct virtio_pci_legacy_device ldev;
		struct virtio_pci_modern_device mdev;
	};
	bool is_legacy;

	/* Where to read and clear interrupt */
	u8 __iomem *isr;

	/* a list of queues so we can dispatch IRQs */
	spinlock_t lock;
	struct list_head virtqueues;

	/* array of all queues for house-keeping */
	struct virtio_pci_vq_info **vqs;

	/* MSI-X support */
	int msix_enabled;
	int intx_enabled;
	cpumask_var_t *msix_affinity_masks;
	/* Name strings for interrupts. This size should be enough,
	 * and I'm too lazy to allocate each name separately. */
	char (*msix_names)[256];
	/* Number of available vectors */
	unsigned int msix_vectors;
	/* Vectors allocated, excluding per-vq vectors if any */
	unsigned int msix_used_vectors;

	/* Whether we have vector per vq */
	bool per_vq_vectors;

	struct virtqueue *(*setup_vq)(struct virtio_pci_device *vp_dev,
				      struct virtio_pci_vq_info *info,
				      unsigned int idx,
				      void (*callback)(struct virtqueue *vq),
				      const char *name,
				      bool ctx,
				      u16 msix_vec);
	void (*del_vq)(struct virtio_pci_vq_info *info);

	u16 (*config_vector)(struct virtio_pci_device *vp_dev, u16 vector);
};

virtio_pci_modern_probe执行完成后,相关数据结构如下图所示:

QEMU源码全解析 —— virtio(20),KVM,QEMU,QEMU,KVM

回到virtio_pci_probe函数。在Linux内核源码/drivers/virtio/virtio_pci_common.c中,代码如下:

static int virtio_pci_probe(struct pci_dev *pci_dev,
			    const struct pci_device_id *id)
{
	struct virtio_pci_device *vp_dev, *reg_dev = NULL;
	int rc;

	/* allocate our structure and fill it out */
	vp_dev = kzalloc(sizeof(struct virtio_pci_device), GFP_KERNEL);
	if (!vp_dev)
		return -ENOMEM;

	pci_set_drvdata(pci_dev, vp_dev);
	vp_dev->vdev.dev.parent = &pci_dev->dev;
	vp_dev->vdev.dev.release = virtio_pci_release_dev;
	vp_dev->pci_dev = pci_dev;
	INIT_LIST_HEAD(&vp_dev->virtqueues);
	spin_lock_init(&vp_dev->lock);

	/* enable the device */
	rc = pci_enable_device(pci_dev);
	if (rc)
		goto err_enable_device;

	if (force_legacy) {
		rc = virtio_pci_legacy_probe(vp_dev);
		/* Also try modern mode if we can't map BAR0 (no IO space). */
		if (rc == -ENODEV || rc == -ENOMEM)
			rc = virtio_pci_modern_probe(vp_dev);
		if (rc)
			goto err_probe;
	} else {
		rc = virtio_pci_modern_probe(vp_dev);
		if (rc == -ENODEV)
			rc = virtio_pci_legacy_probe(vp_dev);
		if (rc)
			goto err_probe;
	}

	pci_set_master(pci_dev);

	rc = register_virtio_device(&vp_dev->vdev);
	reg_dev = vp_dev;
	if (rc)
		goto err_register;

	return 0;

err_register:
	if (vp_dev->is_legacy)
		virtio_pci_legacy_remove(vp_dev);
	else
		virtio_pci_modern_remove(vp_dev);
err_probe:
	pci_disable_device(pci_dev);
err_enable_device:
	if (reg_dev)
		put_device(&vp_dev->vdev.dev);
	else
		kfree(vp_dev);
	return rc;
}

接QEMU源码全解析 —— virtio(18)中的内容,前文书讲到了virtio_pci_probe函数的第5步,

“(5)调用virtio_pci_legacy_probe或者virtio_pci_modern_probe函数来初始化该PCI设备对应的virtio设备。”,继续往下进行。

(6)virtio_pci_probe函数在调用virtio_pci_modern_probe函数之后,接下来会调用register_virtio_device。代码片段如下:

	rc = register_virtio_device(&vp_dev->vdev);
	reg_dev = vp_dev;
	if (rc)
		goto err_register;

register_virtio_device函数在Linux内核源码/drivers/virtio/virtio.c中,代码如下:

/**
 * register_virtio_device - register virtio device
 * @dev        : virtio device to be registered
 *
 * On error, the caller must call put_device on &@dev->dev (and not kfree),
 * as another code path may have obtained a reference to @dev.
 *
 * Returns: 0 on suceess, -error on failure
 */
int register_virtio_device(struct virtio_device *dev)
{
	int err;

	dev->dev.bus = &virtio_bus;
	device_initialize(&dev->dev);

	/* Assign a unique device index and hence name. */
	err = ida_alloc(&virtio_index_ida, GFP_KERNEL);
	if (err < 0)
		goto out;

	dev->index = err;
	err = dev_set_name(&dev->dev, "virtio%u", dev->index);
	if (err)
		goto out_ida_remove;

	err = virtio_device_of_init(dev);
	if (err)
		goto out_ida_remove;

	spin_lock_init(&dev->config_lock);
	dev->config_enabled = false;
	dev->config_change_pending = false;

	INIT_LIST_HEAD(&dev->vqs);
	spin_lock_init(&dev->vqs_list_lock);

	/* We always start by resetting the device, in case a previous
	 * driver messed it up.  This also tests that code path a little. */
	virtio_reset_device(dev);

	/* Acknowledge that we've seen the device. */
	virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);

	/*
	 * device_add() causes the bus infrastructure to look for a matching
	 * driver.
	 */
	err = device_add(&dev->dev);
	if (err)
		goto out_of_node_put;

	return 0;

out_of_node_put:
	of_node_put(dev->dev.of_node);
out_ida_remove:
	ida_free(&virtio_index_ida, dev->index);
out:
	virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
	return err;
}
EXPORT_SYMBOL_GPL(register_virtio_device);

前文已提到,vp_dev->vdev的类型为struct virtio_device,而传给register_virtio_device函数的实参为vp_dev->vdev的地址,即&vp_dev->vdev。从函数名以及参数类型就能看出,register_virtio_device函数的作用是将一个virtio device注册到系统中。具体步骤如下:

(1)设置virtio设备的Bus为virtio_bus。代码片段如下:

    dev->dev.bus = &virtio_bus;

virtio_bus在系统初始化的时候会注册到系统中。

virtio_bus在Linux内核源码/drivers/virtio/virtio.c中初始化,代码如下:

static struct bus_type virtio_bus = {
	.name  = "virtio",
	.match = virtio_dev_match,
	.dev_groups = virtio_dev_groups,
	.uevent = virtio_uevent,
	.probe = virtio_dev_probe,
	.remove = virtio_dev_remove,
};


int register_virtio_driver(struct virtio_driver *driver)
{
	/* Catch this early. */
	BUG_ON(driver->feature_table_size && !driver->feature_table);
	driver->driver.bus = &virtio_bus;
	return driver_register(&driver->driver);
}
EXPORT_SYMBOL_GPL(register_virtio_driver);

在系统初始化的时候,通过register_virtio_driver函数注册到系统中。

(2)设置virtio设备的名字为类似"virtio0"、"virtio1"的字符串。代码片段如下:

    /* Assign a unique device index and hence name. */
	err = ida_alloc(&virtio_index_ida, GFP_KERNEL);
	if (err < 0)
		goto out;

	dev->index = err;
	err = dev_set_name(&dev->dev, "virtio%u", dev->index);
	if (err)
		goto out_ida_remove;

dev_set_name函数在Linux内核源码/drivers/base/core.c中,代码如下:

/**
 * dev_set_name - set a device name
 * @dev: device
 * @fmt: format string for the device's name
 */
int dev_set_name(struct device *dev, const char *fmt, ...)
{
	va_list vargs;
	int err;

	va_start(vargs, fmt);
	err = kobject_set_name_vargs(&dev->kobj, fmt, vargs);
	va_end(vargs);
	return err;
}
EXPORT_SYMBOL_GPL(dev_set_name);

(3)然后调用virtio_reset_device函数重置设备。代码片段如下:

    /* We always start by resetting the device, in case a previous
	 * driver messed it up.  This also tests that code path a little. */
	virtio_reset_device(dev);

(4)最后,调用device_add函数,将设备注册到系统中。代码片段如下:

    /*
	 * device_add() causes the bus infrastructure to look for a matching
	 * driver.
	 */
	err = device_add(&dev->dev);
	if (err)
		goto out_of_node_put;

这里,老版本代码中是调用的是device_register函数。device_register函数跟设备驱动相关性较大,在此简单介绍一下其作用。

device_register函数在Linux内核源码/drivers/base/core.c中,代码如下:

/**
 * device_register - register a device with the system.
 * @dev: pointer to the device structure
 *
 * This happens in two clean steps - initialize the device
 * and add it to the system. The two steps can be called
 * separately, but this is the easiest and most common.
 * I.e. you should only call the two helpers separately if
 * have a clearly defined need to use and refcount the device
 * before it is added to the hierarchy.
 *
 * For more information, see the kerneldoc for device_initialize()
 * and device_add().
 *
 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up the
 * reference initialized in this function instead.
 */
int device_register(struct device *dev)
{
	device_initialize(dev);
	return device_add(dev);
}
EXPORT_SYMBOL_GPL(device_register);

device_register函数向系统注册一个设备。其分为两个简单的步骤——初始化设备(device_initialize(dev))并将其添加到系统中(device_add(dev))。这两个步骤可以分别调用,但放在一起即使用device_register函数是最简单和最常见的。例如,如果有明确的需求在其添加到层级之前使用和重新计数设备,那么应该分别独立地调用这两个助手(函数)。

从此处的代码就可以知道,老版本的内核代码中确实是直接调用了device_register函数,而新版本内核代码在此处则是在register_virtio_device函数的前边先调用了device_initialize(&dev->dev),而后在这里调用了device_add(&dev->dev)。即采用了分开调用的方式。

device_register函数会调用device_add函数,将设备加到系统中,并且会发送一个uevent消息到用户空间,这个uevent消息中包含了virtio设备的vendor id、device id。 udev接收到此消息之后,会加载virtio设备对应的驱动。然后,device_add函数会调用bus_probe_device函数,最终调用到Bus的probe函数和设备的probe函数,也就是virtio_dev_probe函数和virtballoon_probe函数。

device_add函数也在Linux内核源码/drivers/base/core.c中,就在device_register函数上边,代码如下:

/**
 * device_add - add device to device hierarchy.
 * @dev: device.
 *
 * This is part 2 of device_register(), though may be called
 * separately _iff_ device_initialize() has been called separately.
 *
 * This adds @dev to the kobject hierarchy via kobject_add(), adds it
 * to the global and sibling lists for the device, then
 * adds it to the other relevant subsystems of the driver model.
 *
 * Do not call this routine or device_register() more than once for
 * any device structure.  The driver model core is not designed to work
 * with devices that get unregistered and then spring back to life.
 * (Among other things, it's very hard to guarantee that all references
 * to the previous incarnation of @dev have been dropped.)  Allocate
 * and register a fresh new struct device instead.
 *
 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up your
 * reference instead.
 *
 * Rule of thumb is: if device_add() succeeds, you should call
 * device_del() when you want to get rid of it. If device_add() has
 * *not* succeeded, use *only* put_device() to drop the reference
 * count.
 */
int device_add(struct device *dev)
{
	struct subsys_private *sp;
	struct device *parent;
	struct kobject *kobj;
	struct class_interface *class_intf;
	int error = -EINVAL;
	struct kobject *glue_dir = NULL;

	dev = get_device(dev);
	if (!dev)
		goto done;

	if (!dev->p) {
		error = device_private_init(dev);
		if (error)
			goto done;
	}

	/*
	 * for statically allocated devices, which should all be converted
	 * some day, we need to initialize the name. We prevent reading back
	 * the name, and force the use of dev_name()
	 */
	if (dev->init_name) {
		error = dev_set_name(dev, "%s", dev->init_name);
		dev->init_name = NULL;
	}

	if (dev_name(dev))
		error = 0;
	/* subsystems can specify simple device enumeration */
	else if (dev->bus && dev->bus->dev_name)
		error = dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);
	else
		error = -EINVAL;
	if (error)
		goto name_error;

	pr_debug("device: '%s': %s\n", dev_name(dev), __func__);

	parent = get_device(dev->parent);
	kobj = get_device_parent(dev, parent);
	if (IS_ERR(kobj)) {
		error = PTR_ERR(kobj);
		goto parent_error;
	}
	if (kobj)
		dev->kobj.parent = kobj;

	/* use parent numa_node */
	if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
		set_dev_node(dev, dev_to_node(parent));

	/* first, register with generic layer. */
	/* we require the name to be set before, and pass NULL */
	error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
	if (error) {
		glue_dir = kobj;
		goto Error;
	}

	/* notify platform of device entry */
	device_platform_notify(dev);

	error = device_create_file(dev, &dev_attr_uevent);
	if (error)
		goto attrError;

	error = device_add_class_symlinks(dev);
	if (error)
		goto SymlinkError;
	error = device_add_attrs(dev);
	if (error)
		goto AttrsError;
	error = bus_add_device(dev);
	if (error)
		goto BusError;
	error = dpm_sysfs_add(dev);
	if (error)
		goto DPMError;
	device_pm_add(dev);

	if (MAJOR(dev->devt)) {
		error = device_create_file(dev, &dev_attr_dev);
		if (error)
			goto DevAttrError;

		error = device_create_sys_dev_entry(dev);
		if (error)
			goto SysEntryError;

		devtmpfs_create_node(dev);
	}

	/* Notify clients of device addition.  This call must come
	 * after dpm_sysfs_add() and before kobject_uevent().
	 */
	bus_notify(dev, BUS_NOTIFY_ADD_DEVICE);
	kobject_uevent(&dev->kobj, KOBJ_ADD);

	/*
	 * Check if any of the other devices (consumers) have been waiting for
	 * this device (supplier) to be added so that they can create a device
	 * link to it.
	 *
	 * This needs to happen after device_pm_add() because device_link_add()
	 * requires the supplier be registered before it's called.
	 *
	 * But this also needs to happen before bus_probe_device() to make sure
	 * waiting consumers can link to it before the driver is bound to the
	 * device and the driver sync_state callback is called for this device.
	 */
	if (dev->fwnode && !dev->fwnode->dev) {
		dev->fwnode->dev = dev;
		fw_devlink_link_device(dev);
	}

	bus_probe_device(dev);

	/*
	 * If all driver registration is done and a newly added device doesn't
	 * match with any driver, don't block its consumers from probing in
	 * case the consumer device is able to operate without this supplier.
	 */
	if (dev->fwnode && fw_devlink_drv_reg_done && !dev->can_match)
		fw_devlink_unblock_consumers(dev);

	if (parent)
		klist_add_tail(&dev->p->knode_parent,
			       &parent->p->klist_children);

	sp = class_to_subsys(dev->class);
	if (sp) {
		mutex_lock(&sp->mutex);
		/* tie the class to the device */
		klist_add_tail(&dev->p->knode_class, &sp->klist_devices);

		/* notify any interfaces that the device is here */
		list_for_each_entry(class_intf, &sp->interfaces, node)
			if (class_intf->add_dev)
				class_intf->add_dev(dev);
		mutex_unlock(&sp->mutex);
		subsys_put(sp);
	}
done:
	put_device(dev);
	return error;
 SysEntryError:
	if (MAJOR(dev->devt))
		device_remove_file(dev, &dev_attr_dev);
 DevAttrError:
	device_pm_remove(dev);
	dpm_sysfs_remove(dev);
 DPMError:
	dev->driver = NULL;
	bus_remove_device(dev);
 BusError:
	device_remove_attrs(dev);
 AttrsError:
	device_remove_class_symlinks(dev);
 SymlinkError:
	device_remove_file(dev, &dev_attr_uevent);
 attrError:
	device_platform_notify_remove(dev);
	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
	glue_dir = get_glue_dir(dev);
	kobject_del(&dev->kobj);
 Error:
	cleanup_glue_dir(dev, glue_dir);
parent_error:
	put_device(parent);
name_error:
	kfree(dev->p);
	dev->p = NULL;
	goto done;
}
EXPORT_SYMBOL_GPL(device_add);

其中的代码片段:

    /* Notify clients of device addition.  This call must come
	 * after dpm_sysfs_add() and before kobject_uevent().
	 */
	bus_notify(dev, BUS_NOTIFY_ADD_DEVICE);
	kobject_uevent(&dev->kobj, KOBJ_ADD);

    bus_probe_device(dev);

就是上边所讲到的:

device_register函数会调用device_add函数,将设备加到系统中,并且会发送一个uevent消息到用户空间,这个uevent消息中包含了virtio设备的vendor id、device id。 udev接收到此消息之后,会加载virtio设备对应的驱动。

然后,device_add函数会调用bus_probe_device函数,最终调用到Bus的probe函数和设备的probe函数,也就是virtio_dev_probe函数和virtballoon_probe函数。

欲知后事如何,且看下回分解。文章来源地址https://www.toymoban.com/news/detail-833246.html

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