Linux設備模型是由總線(bus_type),設備(device),驅動(device_driver)這三個數據結構來描述的。在設備模型中,所有的設備都通過總線來連接。即使有些設備沒有連接到一根物理上的總線,Linux爲其設置了一個內部的,虛擬的platform總線,來維持總線,驅動,設備的關係。總線是處理器與一個或者多個設備之間的通道。比如一個USB控制器通常是一個PCI設備,設備模型展示了總線和他們所控制的設備之間的連接。linux設備模型中,總線由bus_type結構表示,定義在<linux/device.h>
struct bus_type {
const char *name; //總線類型的名稱
struct bus_attribute *bus_attrs; //總線屬性
struct device_attribute *dev_attrs; //設備屬性
struct driver_attribute *drv_attrs; //驅動屬性
int (*match)(struct device *dev, struct device_driver *drv);
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
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 (*suspend_late)(struct device *dev, pm_message_t state);
int (*resume_early)(struct device *dev);
int (*resume)(struct device *dev);
struct dev_pm_ops *pm;
struct bus_type_private *p;
};
struct bus_type_private {
struct kset subsys; //該總線的subsystem
struct kset *drivers_kset; //所有與該總線相關的驅動集合
struct kset *devices_kset; //所有掛接在該總線上的設備集合
struct klist klist_devices;
struct klist klist_drivers;
struct blocking_notifier_head bus_notifier;
unsigned int drivers_autoprobe:1;
struct bus_type *bus;
};
總線的註冊使用bus_register(struct bus_type *bus)若成功,新的總線將被添加進系統,並可在sysfs的/sys/bus下看到
總線的刪除使用void bus_unregister(struct bus_type *bus)
我們在深入看bus_register這個函數
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int bus_register(struct bus_type *bus)
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{
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int retval;
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struct bus_type_private *priv;
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priv = kzalloc(sizeof(struct bus_type_private), GFP_KERNEL);
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if (!priv)
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return -ENOMEM;
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priv->busbus = bus;
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bus->p = priv;
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BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);
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retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);
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if (retval)
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goto out;
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priv->subsys.kobj.kset = bus_kset;
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priv->subsys.kobj.ktype = &bus_ktype;
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priv->drivers_autoprobe = 1;
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retval = kset_register(&priv->subsys);
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if (retval)
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goto out;
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retval = bus_create_file(bus, &bus_attr_uevent);
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if (retval)
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goto bus_uevent_fail;
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-
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priv->devices_kset = kset_create_and_add("devices", NULL,
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&priv->subsys.kobj);
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if (!priv->devices_kset) {
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retval = -ENOMEM;
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goto bus_devices_fail;
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}
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priv->drivers_kset = kset_create_and_add("drivers", NULL,
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&priv->subsys.kobj);
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if (!priv->drivers_kset) {
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retval = -ENOMEM;
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goto bus_drivers_fail;
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}
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klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
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klist_init(&priv->klist_drivers, NULL, NULL);
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retval = add_probe_files(bus);
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if (retval)
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goto bus_probe_files_fail;
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retval = bus_add_attrs(bus);
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if (retval)
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goto bus_attrs_fail;
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pr_debug("bus: '%s': registered\n", bus->name);
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return 0;
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bus_attrs_fail:
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remove_probe_files(bus);
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bus_probe_files_fail:
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kset_unregister(bus->p->drivers_kset);
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bus_drivers_fail:
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kset_unregister(bus->p->devices_kset);
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bus_devices_fail:
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bus_remove_file(bus, &bus_attr_uevent);
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bus_uevent_fail:
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kset_unregister(&bus->p->subsys);
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kfree(bus->p);
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out:
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return retval;
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}
從這裏
priv->subsys.kobj.kset = bus_kset;
priv->subsys.kobj.ktype = &bus_ktype;
可以看得出總線初始化了自己的kset對象。kset在後續文件中有講到。
int (*match)(struct device *dev, struct device_driver *drv);匹配設備和驅動程序。
當一個新設備或者驅動被添加到這個總線時,該方法被調用,用於判斷指定的驅動和諧是否能處理指定的設備。若可以,則返回非零值。後面的測試程序採用匹配設備的dev->bus_id字符串和驅動的drv->name字符串是否相同來判斷驅動是否能處理該設備。
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
在爲用戶空間產生熱插拔事件之前,這個方法允許總線添加環境變量
總線屬性由bus_attribute結構描述
struct bus_attribute {
struct attribute attr;
ssize_t (*show)(struct bus_type *bus, char *buf);
ssize_t (*store)(struct bus_type *bus, const char *buf, size_t count);
};
創建屬性
int bus_create_file(struct bus_type *bus,struct bus_attribute *attr)
刪除屬性
int bus_remove_file(struct bus_type *bus,struct bus_attribute *attr)
注意下面這個內核定義的宏後面的例子會用到
#define BUS_ATTR(_name, _mode, _show, _store)
\
struct bus_attribute bus_attr_##_name = __ATTR(_name, _mode, _show, _store)
在編譯時創建和初始化bus_attribute結構,它將bus_attr_作爲給定前綴來創建總線的真正名稱。
如:static BUS_ATTR(version, S_IRUGO, show_bus_version, NULL);
將創建一個bus_attr_version結構體對象。
添加總線例子:
#include <linux/device.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
MODULE_AUTHOR("David Xie");
MODULE_LICENSE("Dual BSD/GPL");
static char *Version = "$Revision: 1.9 $";
static int my_match(struct device *dev, struct device_driver *driver)
{
return !strncmp(dev->bus_id, driver->name, strlen(driver->name));
}
static void my_bus_release(struct device *dev)
{
printk(KERN_DEBUG "my bus release\n");
}
struct device my_bus = {
.bus_id = "my_bus0",
.release = my_bus_release
};
struct bus_type my_bus_type = {
.name = "my_bus",
.match = my_match,
};
EXPORT_SYMBOL(my_bus);
EXPORT_SYMBOL(my_bus_type);
/*
* Export a simple attribute.
*/
static ssize_t show_bus_version(struct bus_type *bus, char *buf)
{
return snprintf(buf, PAGE_SIZE, "%s\n", Version);
}
static BUS_ATTR(version, S_IRUGO, show_bus_version, NULL);
static int __init my_bus_init(void)
{
int ret;
/*註冊總線*/
ret = bus_register(&my_bus_type);
if (ret)
return ret;
/*創建屬性文件*/
if (bus_create_file(&my_bus_type, &bus_attr_version))
printk(KERN_NOTICE "Fail to create version attribute!\n");
/*註冊總線設備*/
ret = device_register(&my_bus);
if (ret)
printk(KERN_NOTICE "Fail to register device:my_bus!\n");
return ret;
}
static void my_bus_exit(void)
{
device_unregister(&my_bus);
bus_unregister(&my_bus_type);
}
module_init(my_bus_init);
module_exit(my_bus_exit);
創建一條名爲my_bus_type的總線和一個名爲my_bus的總線設備,注意總線也是一個設備,也需要註冊。
測試結果:
運行後,查看/sys/bus/目錄
ls /sys/bus/
acpi i2c mdio_bus my_bus pci_express platform scsi usb
hid isa pci pcmcia