linux通知链相关

一.头文件

#include <linux/notifier.h>

二.结构体

//通知块 
struct notifier_block {
	int (*notifier_call)(struct notifier_block *, unsigned long, void *);	//回调函数
	struct notifier_block __rcu *next;	//指向通知链表的下一项
	int priority;	//优先级
};
//原子通知链 运行在中断上下文,不允许阻塞
struct atomic_notifier_head {
	spinlock_t lock;
	struct notifier_block __rcu *head;
};
//阻塞通知链 运行在进程上下文,允许阻塞
struct blocking_notifier_head {
	struct rw_semaphore rwsem;
	struct notifier_block __rcu *head;
};
//原始通知链,锁和保护机制由调用者维护
struct raw_notifier_head {
	struct notifier_block __rcu *head;
};
//SRCU通知链 阻塞通知链的变体
struct srcu_notifier_head {
	struct mutex mutex;
	struct srcu_struct srcu;
	struct notifier_block __rcu *head;
};

三.通知链头初始化

调用定义好的宏初始化通知链表头

#define ATOMIC_NOTIFIER_HEAD(name)				\
	struct atomic_notifier_head name =	ATOMIC_NOTIFIER_INIT(name)
#define BLOCKING_NOTIFIER_HEAD(name)				\
	struct blocking_notifier_head name =	BLOCKING_NOTIFIER_INIT(name)
#define RAW_NOTIFIER_HEAD(name)				\
	struct raw_notifier_head name = RAW_NOTIFIER_INIT(name)

定义通知链表头结构体,然后初始化赋值

#define ATOMIC_NOTIFIER_INIT(name) {				\
		.lock = __SPIN_LOCK_UNLOCKED(name.lock),	\
		.head = NULL }
#define BLOCKING_NOTIFIER_INIT(name) {			\
		.rwsem = __RWSEM_INITIALIZER((name).rwsem),	\
		.head = NULL }
#define RAW_NOTIFIER_INIT(name)	{			\
		.head = NULL }

SRCU通知链不支持静态调用

四.注册注销通知块

1.注册通知块

int atomic_notifier_chain_register(struct atomic_notifier_head *nh,struct notifier_block *nb);
int blocking_notifier_chain_register(struct blocking_notifier_head *nh,struct notifier_block *nb);
int raw_notifier_chain_register(struct raw_notifier_head *nh,struct notifier_block *nb);
int srcu_notifier_chain_register(struct srcu_notifier_head *nh,struct notifier_block *nb);
int blocking_notifier_chain_cond_register(struct blocking_notifier_head *nh,struct notifier_block *nb);

最终调用notifier_chain_register

static int notifier_chain_register(struct notifier_block **nl,struct notifier_block *n)
{
	while ((*nl) != NULL) {	//若链表项非空
		if (n->priority > (*nl)->priority)
			break;
		nl = &((*nl)->next);	//则nl指向其下一链表项
	}
	n->next = *nl;	//将通知链表项添加进通知链表
	rcu_assign_pointer(*nl, n);
	return 0;
}

2.注销通知块

int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,struct notifier_block *n)
int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,struct notifier_block *n)
int raw_notifier_chain_unregister(struct raw_notifier_head *nh,struct notifier_block *n)
int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,struct notifier_block *n)

最终调用

static int notifier_chain_unregister(struct notifier_block **nl,struct notifier_block *n)
{
	while ((*nl) != NULL) {
		if ((*nl) == n) {
			rcu_assign_pointer(*nl, n->next);
			return 0;
		}
		nl = &((*nl)->next);	//从通知链表中移除通知块
	}
	return -ENOENT;
}

五.通知通知链

int __kprobes atomic_notifier_call_chain(struct atomic_notifier_head *nh,unsigned long val, void *v)
int blocking_notifier_call_chain(struct blocking_notifier_head *nh,unsigned long val, void *v)
int raw_notifier_call_chain(struct raw_notifier_head *nh,unsigned long val, void *v)
int srcu_notifier_call_chain(struct srcu_notifier_head *nh,unsigned long val, void *v)

最终会调用

static int __kprobes notifier_call_chain(struct notifier_block **nl,unsigned long val, void *v,int nr_to_call,	int *nr_calls)
{
	int ret = NOTIFY_DONE;
	struct notifier_block *nb, *next_nb;

	nb = rcu_dereference_raw(*nl);

	while (nb && nr_to_call) {	//遍历整个通知链
		next_nb = rcu_dereference_raw(nb->next);

#ifdef CONFIG_DEBUG_NOTIFIERS
		if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
			WARN(1, "Invalid notifier called!");
			nb = next_nb;
			continue;
		}
#endif
		ret = nb->notifier_call(nb, val, v);	//调用通知块的notifier_call函数

		if (nr_calls)
			(*nr_calls)++;

		if ((ret & NOTIFY_STOP_MASK) == NOTIFY_STOP_MASK)
			break;
		nb = next_nb;	//指向下一通知块
		nr_to_call--;
	}
	return ret;
}

六.运用

发送通知者:定义通知块及回调函数,注册通知块

接收通知者:,通知通知链

在drivers/usb/core/usb.c中
定义了通识块及其回调函数
static struct notifier_block usb_bus_nb = {
 .notifier_call = usb_bus_notify,
};
在drivers/usb/core/usb.c中usb_init函数中
注册了总线通知链
 retval = bus_register_notifier(&usb_bus_type, &usb_bus_nb);
总线通知链中注册了阻塞通知链
int bus_register_notifier(struct bus_type *bus, struct notifier_block *nb)
{
 return blocking_notifier_chain_register(&bus->p->bus_notifier, nb);
}

通知者
1.有设备添加
device_register
 device_add
 
 if (dev->bus)
  blocking_notifier_call_chain(&dev->bus->p->bus_notifier,BUS_NOTIFY_ADD_DEVICE, dev);
2.有设备移除
device_unregister
 device_del 
 
 if (dev->bus)
  blocking_notifier_call_chain(&dev->bus->p->bus_notifier,BUS_NOTIFY_DEL_DEVICE, dev);

通知链回调函数

static int usb_bus_notify(struct notifier_block *nb, unsigned long action,void *data)
{
	struct device *dev = data;
	//回调函数根据传递进来的参数获得设备文件及行为标识,对设备添加和移除做分别处理
	switch (action) {
	case BUS_NOTIFY_ADD_DEVICE:
		if (dev->type == &usb_device_type)
			(void) usb_create_sysfs_dev_files(to_usb_device(dev));
		else if (dev->type == &usb_if_device_type)
			(void) usb_create_sysfs_intf_files(to_usb_interface(dev));
		break;

	case BUS_NOTIFY_DEL_DEVICE:
		if (dev->type == &usb_device_type)
			usb_remove_sysfs_dev_files(to_usb_device(dev));
		else if (dev->type == &usb_if_device_type)
			usb_remove_sysfs_intf_files(to_usb_interface(dev));
		break;
	}
	return 0;
}