switch 类
1. init/exit:
static int __init switch_class_init(void)
{
return create_switch_class(); //新建一个switch类
}
static void __exit switch_class_exit(void)
{
class_destroy(switch_class); //销毁一个switch类
}
module_init(switch_class_init);
module_exit(switch_class_exit);
2. create_switch_class
(
)
struct class *switch_class; //声明两个全局变量
static atomic_t device_count;
static int create_switch_class(void)
{
if (!switch_class) {
switch_class = class_create(THIS_MODULE, "switch"); //给this module创建一个switch类.
if (IS_ERR(switch_class))
return PTR_ERR(switch_class);
atomic_set(&device_count, 0); //初始化一个原子变量,用来保护临界区。
}
return 0;
}
3. switch_dev_register(): 设备注册函数,提供给别的驱动调用,用来注册switch设备。
int switch_dev_register(struct switch_dev *sdev)
{
int ret;
if (!switch_class) {
ret = create_switch_class(); //如果没有switch类,则创建一个。
if (ret < 0)
return ret;
}
sdev->index = atomic_inc_return(&device_count); //原子变量+1,以获得原子锁,进入临界区操作。
sdev->dev = device_create(switch_class, NULL,
MKDEV(0, sdev->index), NULL, sdev->name); //创建一个名为sdev->name,设备号为MKDEV(0, sdev->index)的switch类设备。
if (IS_ERR(sdev->dev)) //如果创建不成功就返回。
return PTR_ERR(sdev->dev);
ret = device_create_file(sdev->dev, &dev_attr_state); //为设备添加 sysfs attribute:state。
if (ret < 0)
goto err_create_file_1;
ret = device_create_file(sdev->dev, &dev_attr_name); //为设备添加 sysfs attribute:name
if (ret < 0)
goto err_create_file_2;
dev_set_drvdata(sdev->dev, sdev); //给设备初始化。
sdev->state = 0;
return 0;
err_create_file_2:
device_remove_file(sdev->dev, &dev_attr_state);
err_create_file_1:
device_destroy(switch_class, MKDEV(0, sdev->index));
printk(KERN_ERR "switch: Failed to register driver %s\n", sdev->name);
return ret;
}
EXPORT_SYMBOL_GPL(switch_dev_register);
4. 注册完一个switch设备之后,就可以给该switch设备设置状态了, 即:
switch_set_state()
void switch_set_state(struct switch_dev *sdev, int state)
{
char name_buf[120];
char state_buf[120];
char *prop_buf;
char *envp[3];
int env_offset = 0;
int length;
if (sdev->state != state) {
sdev->state = state; //如果设备状态不等于state,则赋值state.
prop_buf = (char *)get_zeroed_page(GFP_KERNEL); //获得一页初始化为0的内存 prop_buf。
if (prop_buf) {
length = name_show(sdev->dev, NULL, prop_buf); //输出设备名 到prop_buf 中.
if (length > 0) {
if (prop_buf[length - 1] == '\n')
prop_buf[length - 1] = 0;
snprintf(name_buf, sizeof(name_buf),
"SWITCH_NAME=%s", prop_buf); //打印switch name
envp[env_offset++] = name_buf;
}
length = state_show(sdev->dev, NULL, prop_buf);
if (length > 0) {
if (prop_buf[length - 1] == '\n')
prop_buf[length - 1] = 0;
snprintf(state_buf, sizeof(state_buf), //打印switch state
"SWITCH_STATE=%s", prop_buf);
envp[env_offset++] = state_buf;
}
envp[env_offset] = NULL;
kobject_uevent_env(&sdev->dev->kobj, KOBJ_CHANGE, envp); //给该switch设备传输一份带envp[]的数据。
free_page((unsigned long)prop_buf); //释放申请的内存。
} else {
printk(KERN_ERR "out of memory in switch_set_state\n");
kobject_uevent(&sdev->dev->kobj, KOBJ_CHANGE); //notify userspace by ending an uevent 通知用户空间,uevent操作结束。
}
}
}
EXPORT_SYMBOL_GPL(switch_set_state);
5. name 和 state 属性操作
static ssize_t state_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct switch_dev *sdev = (struct switch_dev *)
dev_get_drvdata(dev);
if (sdev->print_state) {
int ret = sdev->print_state(sdev, buf); //打印state
if (ret >= 0)
return ret;
}
return sprintf(buf, "%d\n", sdev->state);
}
static ssize_t name_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct switch_dev *sdev = (struct switch_dev *)
dev_get_drvdata(dev);
if (sdev->print_name) {
int ret = sdev->print_name(sdev, buf); //打印name
if (ret >= 0)
return ret;
}
return sprintf(buf, "%s\n", sdev->name);
}
static DEVICE_ATTR(state, S_IRUGO | S_IWUSR, state_show, NULL); //给用户空间提供接口
static DEVICE_ATTR(name, S_IRUGO | S_IWUSR, name_show, NULL);
struct switch_dev {
const char *name;
struct device *dev;
int index;
int state;
ssize_t (*print_name)(struct switch_dev *sdev, char *buf);
ssize_t (*print_state)(struct switch_dev *sdev, char *buf);
};