The Basic Device Structure
基本设备结构体
~~~~~~~~~~~~~~~~~~~~~~~~~~
See the kerneldoc for the struct device.
Programming Interface
编程接口
~~~~~~~~~~~~~~~~~~~~~
The bus driver that discovers the device uses this to register the
device with the core:
那些发现了设备的总线驱动使用以下接口将这个设备注册到核心：
- int device_register(struct device * dev);
The bus should initialize the following fields:
总线应该初始化该设备的下列字段：
- parent
- name
- bus_id
- bus
A device is removed from the core when its reference count goes to
0. The reference count can be adjusted using:
当一个设备的引用计数减到 0 时应该从核心中移除该设备。可以使用以下
接口改变一个设备的引用计数。
- struct device * get_device(struct device * dev);
- void put_device(struct device * dev);
get_device() will return a pointer to the struct device passed to it
if the reference is not already 0 (if it's in the process of being
removed already).
如果 device 的引用计数不是 0（已经在移除的过程中）的话，get_device()
会返回一个指向传递给它的 struct device 的指针。
A driver can access the lock in the device structure using:
一个 driver 可以使用以下接口访问 device 结构体中的 lock：
- void lock_device(struct device * dev);
- void unlock_device(struct device * dev);
Attributes
属性
~~~~~~~~~~
- struct device_attribute {
- struct attribute attr;
- ssize_t (*show)(struct device *dev, struct device_attribute *attr,
- char *buf);
- ssize_t (*store)(struct device *dev, struct device_attribute *attr,
- const char *buf, size_t count);
- };
Attributes of devices can be exported by a device driver through sysfs.
设备驱动程序可以通过 sysfs 导出设备的属性。
Please see Documentation/filesystems/sysfs.txt for more information
on how sysfs works.
请参考 Documentation/filesystems/sysfs.txt 来了解 sysfs 如何工作。
As explained in Documentation/kobject.txt, device attributes must be be
created before the KOBJ_ADD uevent is generated. The only way to realize
that is by defining an attribute group.
正如 Documentation/kobject.txt 中所述，设备属性的创建必须在 KOBJ_ADD
uevent 发生之前。实现这个的唯一途径就是定义一个属性组。
Attributes are declared using a macro called DEVICE_ATTR:
定义属性可以使用宏函数 DEVICE_ATTR。
- #define DEVICE_ATTR(name,mode,show,store)
Example:
示例：
- static DEVICE_ATTR(type, 0444, show_type, NULL);
- static DEVICE_ATTR(power, 0644, show_power, store_power);
This declares two structures of type struct device_attribute with respective
names 'dev_attr_type' and 'dev_attr_power'. These two attributes can be
organized as follows into a group:
这将定义两个拥有各自名称的 struct device_attribute 类型的结构体，'dev_attr_type'
和'dev_attr_power'。这两个属性可以象这样组织到一块：
- static struct attribute *dev_attrs[] = {
- &dev_attr_type.attr,
- &dev_attr_power.attr,
- NULL,
- };
- static struct attribute_group dev_attr_group = {
- .attrs = dev_attrs,
- };
- static const struct attribute_group *dev_attr_groups[] = {
- &dev_attr_group,
- NULL,
- };
This array of groups can then be associated with a device by setting the
group pointer in struct device before device_register() is invoked:
这些数组随后可以通过设置 groups 指针在 device_register() 被调用之前关联
到一个 device 上：
- dev->groups = dev_attr_groups;
- device_register(dev);
The device_register() function will use the 'groups' pointer to create the
device attributes and the device_unregister() function will use this pointer
to remove the device attributes.
device_register() 函数将使用‘groups‘指针去创建该设备的属性，而
device_unregister() 函数也将使用‘groups‘指针去移除该设备的属性。
Word of warning: While the kernel allows device_create_file() and
device_remove_file() to be called on a device at any time, userspace has
strict expectations on when attributes get created. When a new device is
registered in the kernel, a uevent is generated to notify userspace (like
udev) that a new device is available. If attributes are added after the
device is registered, then userspace won't get notified and userspace will
not know about the new attributes.
提醒一句：尽管 kernel 允许在任何时候都可以在一个设备上调用 device_create_file()
和 device_remove_file()，但用户空间还是强烈期望能够得知在属性何时被创建。
当一个新的设备注册进 kernel 时，就会产生一个 uevent 事件并通知用户空间该
设备可用了。但如果设备的属性是在设备注册之后才添加的话，那么用户空间将
得不到任何通知，对这个新的属性也将一无所知。
This is important for device driver that need to publish additional
attributes for a device at driver probe time. If the device driver simply
calls device_create_file() on the device structure passed to it, then
userspace will never be notified of the new attributes.
这对于那些需要在驱动探测（driver probe）时为设备发布附加属性的设备驱动
程序来说是很重要的。如果设备驱动程序只是简单的传递 device 结构体来调用
device_create_file() 的话，用户空间就永远也得不到关于新属性的通知。
