大多数驱动程序都要实现一个probe函数，该函数在register时被调用，具体内核是如何实现的呢？下面我们以LINUX内核中Hamachi.c为例子来分析一下：

static struct pci_driver hamachi_driver = {
	.name		= DRV_NAME,
	.id_table	= hamachi_pci_tbl,
	.probe		= hamachi_init_one,
	.remove		= __devexit_p(hamachi_remove_one),
};

static int __init hamachi_init (void)
{
/* when a module, this is printed whether or not devices are found in probe */
#ifdef MODULE
	printk(version);
#endif
	return pci_register_driver(&hamachi_driver);
}

static void __exit hamachi_exit (void)
{
	pci_unregister_driver(&hamachi_driver);
}


module_init(hamachi_init);
module_exit(hamachi_exit);

首先，实现了一个pci_driver结构体，名为hamachi_driver,

在hamachi_init函数中，直接调用pci_register_driver,追踪该函数：

/*
 * pci_register_driver must be a macro so that KBUILD_MODNAME can be expanded
 */
#define pci_register_driver(driver)		\
	__pci_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)

发现pci_register_driver实际上是一个macro，使用宏的目的是扩展参数，实际调用的是__pci_register_driver,继续追踪：

/**
 * __pci_register_driver - register a new pci driver
 * @drv: the driver structure to register
 * @owner: owner module of drv
 * @mod_name: module name string
 * 
 * Adds the driver structure to the list of registered drivers.
 * Returns a negative value on error, otherwise 0. 
 * If no error occurred, the driver remains registered even if 
 * no device was claimed during registration.
 */
int __pci_register_driver(struct pci_driver *drv, struct module *owner,
			  const char *mod_name)
{
	int error;

	/* initialize common driver fields */
	drv->driver.name = drv->name;
	drv->driver.bus = &pci_bus_type;
	drv->driver.owner = owner;
	drv->driver.mod_name = mod_name;

	if (drv->pm)
		drv->driver.pm = &drv->pm->base;

	spin_lock_init(&drv->dynids.lock);
	INIT_LIST_HEAD(&drv->dynids.list);

	/* register with core */
	error = driver_register(&drv->driver);
	if (error)
		return error;

	error = pci_create_newid_file(drv);
	if (error)
		driver_unregister(&drv->driver);

	return error;

}

前面填充了drv->driver结构，然后调用spin_lock_init来初始化自旋锁，调用INIT_LIST_HEAD来初始化一个双向链表，核心是调用了driver_register函数，继续追踪:

int driver_register(struct device_driver *drv)
{
	int ret;
	struct device_driver *other;

	if ((drv->bus->probe && drv->probe) ||
	    (drv->bus->remove && drv->remove) ||
	    (drv->bus->shutdown && drv->shutdown))
		printk(KERN_WARNING "Driver '%s' needs updating - please use "
			"bus_type methods\n", drv->name);

	other = driver_find(drv->name, drv->bus);
	if (other) {
		put_driver(other);
		printk(KERN_ERR "Error: Driver '%s' is already registered, "
			"aborting...\n", drv->name);
		return -EBUSY;
	}

	ret = bus_add_driver(drv);
	if (ret)
		return ret;
	ret = driver_add_groups(drv, drv->groups);
	if (ret)
		bus_remove_driver(drv);
	return ret;
}

该函数首先做了一些检查，实际上是重点是调用了bus_add_drvier函数，进入该函数：

/**
 * bus_add_driver - Add a driver to the bus.
 * @drv: driver.
 */
int bus_add_driver(struct device_driver *drv)
{
	struct bus_type *bus;
	struct driver_private *priv;
	int error = 0;

	bus = bus_get(drv->bus);
	if (!bus)
		return -EINVAL;

	pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv) {
		error = -ENOMEM;
		goto out_put_bus;
	}
	klist_init(&priv->klist_devices, NULL, NULL);
	priv->driver = drv;
	drv->p = priv;
	priv->kobj.kset = bus->p->drivers_kset;
	error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
				     "%s", drv->name);
	if (error)
		goto out_unregister;

	if (drv->bus->p->drivers_autoprobe) {
		error = driver_attach(drv);
		if (error)
			goto out_unregister;
	}
	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
	module_add_driver(drv->owner, drv);

	error = driver_create_file(drv, &driver_attr_uevent);
	if (error) {
		printk(KERN_ERR "%s: uevent attr (%s) failed\n",
			__func__, drv->name);
	}
	error = driver_add_attrs(bus, drv);
	if (error) {
		/* How the hell do we get out of this pickle? Give up */
		printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
			__func__, drv->name);
	}
	error = add_bind_files(drv);
	if (error) {
		/* Ditto */
		printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
			__func__, drv->name);
	}

	kobject_uevent(&priv->kobj, KOBJ_ADD);
	return error;
out_unregister:
	kobject_put(&priv->kobj);
out_put_bus:
	bus_put(bus);
	return error;
}

该函数前面还是一些分配资源和初始化的工作，直到driver_attach函数，该函数的作用是遍历总线上所有的设备，将驱动与设备绑定：

int driver_attach(struct device_driver *drv)
{
    return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}

进入bus_for_each_dev函数中，

int bus_for_each_dev(struct bus_type *bus, struct device *start,
		     void *data, int (*fn)(struct device *, void *))
{
	struct klist_iter i;
	struct device *dev;
	int error = 0;

	if (!bus)
		return -EINVAL;

	klist_iter_init_node(&bus->p->klist_devices, &i,
			     (start ? &start->knode_bus : NULL));
	while ((dev = next_device(&i)) && !error)
		error = fn(dev, data);
	klist_iter_exit(&i);
	return error;
}

该函数的重点是调用了fn这个函数指针实现回调，回调函数为__driver_attach,进入该函数：

static int __driver_attach(struct device *dev, void *data)
{
	struct device_driver *drv = data;

	/*
	 * Lock device and try to bind to it. We drop the error
	 * here and always return 0, because we need to keep trying
	 * to bind to devices and some drivers will return an error
	 * simply if it didn't support the device.
	 *
	 * driver_probe_device() will spit a warning if there
	 * is an error.
	 */

	if (dev->parent)	/* Needed for USB */
		down(&dev->parent->sem);
	down(&dev->sem);
	if (!dev->driver)
		driver_probe_device(drv, dev);
	up(&dev->sem);
	if (dev->parent)
		up(&dev->parent->sem);

	return 0;
}

重点进入driver_probe_device函数，

/**
 * driver_probe_device - attempt to bind device & driver together
 * @drv: driver to bind a device to
 * @dev: device to try to bind to the driver
 *
 * First, we call the bus's match function, if one present, which should
 * compare the device IDs the driver supports with the device IDs of the
 * device. Note we don't do this ourselves because we don't know the
 * format of the ID structures, nor what is to be considered a match and
 * what is not.
 *
 * This function returns 1 if a match is found, -ENODEV if the device is
 * not registered, and 0 otherwise.
 *
 * This function must be called with @dev->sem held.  When called for a
 * USB interface, @dev->parent->sem must be held as well.
 */
int driver_probe_device(struct device_driver *drv, struct device *dev)
{
	int ret = 0;

	if (!device_is_registered(dev))
		return -ENODEV;
	if (drv->bus->match && !drv->bus->match(dev, drv))
		goto done;

	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
		 drv->bus->name, __func__, dev->bus_id, drv->name);

	ret = really_probe(dev, drv);

done:
	return ret;
}

该函数的作用是将设备和驱动程序绑定，首先调用match函数指针，检查设备和驱动是否匹配，然后调用了really_probe，真正的probe：

static int really_probe(struct device *dev, struct device_driver *drv)
{
	int ret = 0;

	atomic_inc(&probe_count);
	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
		 drv->bus->name, __func__, drv->name, dev->bus_id);
	WARN_ON(!list_empty(&dev->devres_head));

	dev->driver = drv;
	if (driver_sysfs_add(dev)) {
		printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
			__func__, dev->bus_id);
		goto probe_failed;
	}

	if (dev->bus->probe) {
		ret = dev->bus->probe(dev);
		if (ret)
			goto probe_failed;
	} else if (drv->probe) {
		ret = drv->probe(dev);
		if (ret)
			goto probe_failed;
	}

	driver_bound(dev);
	ret = 1;
	pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
		 drv->bus->name, __func__, dev->bus_id, drv->name);
	goto done;

probe_failed:
	devres_release_all(dev);
	driver_sysfs_remove(dev);
	dev->driver = NULL;

	if (ret != -ENODEV && ret != -ENXIO) {
		/* driver matched but the probe failed */
		printk(KERN_WARNING
		       "%s: probe of %s failed with error %d\n",
		       drv->name, dev->bus_id, ret);
	}
	/*
	 * Ignore errors returned by ->probe so that the next driver can try
	 * its luck.
	 */
	ret = 0;
done:
	atomic_dec(&probe_count);
	wake_up(&probe_waitqueue);
	return ret;
}

直到这里才利用drv->probe指针，该指针指向的是：

struct device_driver {
    const char        *name;
    struct bus_type        *bus;

    struct module        *owner;
    const char         *mod_name;    /* used for built-in modules */

    int (*probe) (struct device *dev);
    int (*remove) (struct device *dev);
    void (*shutdown) (struct device *dev);
    int (*suspend) (struct device *dev, pm_message_t state);
    int (*resume) (struct device *dev);
    struct attribute_group **groups;

    struct pm_ops *pm;

    struct driver_private *p;
};

中的probe函数指针，该结构体是需要你在register之前实现的，直到此时才
真正的调用了hamachi.c中你实现的probe函数。