Linux庞大系统中,各个模块是相对独立的,那么模块间通信该如何做呢?当然你也可以使用全局资源,如果这样的话系统缺少独立性,会带来稳定性问题的。如果你说,使用共享内存,进程通信等,那么你曲解我的意思了,因为你说的大多是user space的,而我说的是内核模块级别的。notifier_chain,对就是它,实质上这个机制就是一个回调函数链表的操作,回调函数的注册,注销,调用。源系统处(比如A子系统)进行定义初始化和回调函数调用,被通知处(比如B子系统)进行回调函数的注册和注销,那么当A系统发生某种事件是,就调用通知链中所有回调函数,B系统中注册的回调函数就会得到执行。一旦执行回调函数,它会从链表头依次执行每一个回调函数,那么依次执行是一次性全部执行完?执行过程的任意时间都可睡眠?这些需求也就产生了4种类型的notifier_chain。
结构体定义:
- struct notifier_block { /* chain的基本单位 */
- int (*notifier_call)(struct notifier_block *, unsigned long, void *);
- struct notifier_block __rcu *next;
- int priority;
- };
- struct atomic_notifier_head {/* atmoic context; 执行(rcu_read_lock);回调函数执行不能阻塞;实时性高 */
- spinlock_t lock;
- struct notifier_block __rcu *head;
- };
- struct blocking_notifier_head { /* process context;执行(rw_semaphore) ;回调函数执行可以阻塞;实时性相对低*/
- struct rw_semaphore rwsem;
- struct notifier_block __rcu *head;
- };
- struct raw_notifier_head { /* 原始链表操作,注册,执行过程无任何保护,完全有驱动人员控制 */
- struct notifier_block __rcu *head;
- };
- struct srcu_notifier_head { /* process context;可阻塞通知链的变体(Sleepable Read-Copy-Update),回调函数执行可以阻塞 */
- struct mutex mutex;
- struct srcu_struct srcu;
- struct notifier_block __rcu *head;
- };
初始化:
#include <linux/notifier.h>
- #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)
- /* srcu_notifier_heads must be initialized and cleaned up dynamically */
- extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
- #define srcu_cleanup_notifier_head(name) \
- cleanup_srcu_struct(&(name)->srcu);
经过定义及初始化后,一类的链表的头就形成了,注册就是增加节点,执行就是遍历节点,唯一要说明的就是,srcu链需要动态的定义,其他三中不需要。
注册和注销:
- int atomic_notifier_chain_register(struct atomic_notifier_head *nh, struct notifier_block *n);
- int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh, struct notifier_block *n)
- int blocking_notifier_chain_register(struct blocking_notifier_head *nh, struct notifier_block *n);
- /* 注册的notifier_block不重复*/
- int blocking_notifier_chain_cond_register(struct blocking_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_register(struct raw_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_register(struct srcu_notifier_head *nh, struct notifier_block *n);
- int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh, struct notifier_block *n);
其中注册和注销都调用了最基本的函数如下:
- /*
- * Notifier chain core routines. The exported routines below
- * are layered on top of these, with appropriate locking added.
- */
- static int notifier_chain_register(struct notifier_block **nl,
- struct notifier_block *n)
- {
- while ((*nl) != NULL) {
- if (n->priority > (*nl)->priority)
- break;
- nl = &((*nl)->next);
- }
- n->next = *nl;
- rcu_assign_pointer(*nl, n);
- return 0;
- }
- static int notifier_chain_cond_register(struct notifier_block **nl,
- struct notifier_block *n)
- {
- while ((*nl) != NULL) {
- if ((*nl) == n)
- return 0;
- if (n->priority > (*nl)->priority)
- break;
- nl = &((*nl)->next);
- }
- n->next = *nl;
- rcu_assign_pointer(*nl, n);
- return 0;
- }
- 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);
- }
- return -ENOENT;
- }
调用:
当A系统发生事件时,会调用下面函数之一的方法来,执行通知链中的所有回调函数,那么所有注册的地方都会得到执行,除前一个函数执行返回值含有NOTIFY_STOP_MASK标志。其中参数val是一个整形,用户自定义含义的传入值,参数v是一个void*类型,用户自定义任何类型含义,一般为平台结构体指针,使用的时候需要强制转换。
- /*调用了__atomic_notifier_call_chain,且nr_to_call=-1表示回调函数调用个数不限,nr_calls=NULL表示不关心已执行的回调函数个数*/
- extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh, unsigned long val, void *v);
- extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh, unsigned long val, void *v, int nr_to_call, int *nr_calls);
- extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh, unsigned long val, void *v);
- <span style="white-space:pre"> </span>extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh, unsigned long val, void *v, int nr_to_call, int *nr_calls);
- extern int raw_notifier_call_chain(struct raw_notifier_head *nh, unsigned long val, void *v);
- extern int __raw_notifier_call_chain(struct raw_notifier_head *nh, unsigned long val, void *v, int nr_to_call, int *nr_calls);
- extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh, unsigned long val, void *v);
- extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh, unsigned long val, void *v, int nr_to_call, int *nr_calls);
回调函数返回值:
- #define NOTIFY_DONE 0x0000 /* Don't care回调函数不关心返回值*/
- #define NOTIFY_OK 0x0001 /* Suits me 回调函数调用顺利完成*/
- #define NOTIFY_STOP_MASK 0x8000 /* Don't call further 回调函数链禁止继续调用的掩码*/
- #define NOTIFY_BAD (NOTIFY_STOP_MASK|0x0002)
- /* Bad/Veto action 回调函数执行有错*/
- /*
- * Clean way to return from the notifier and stop further calls.当前顺利调用,禁止继续调用
- */
- #define NOTIFY_STOP (NOTIFY_OK|NOTIFY_STOP_MASK)
在notifier_call_chain函数中去依次执行每一个注册的回调函数,并以前一个回调函数的返回值为判断依据,是否继续调用,最后一个执行函数的返回值作为notifier_call_chain的返回值。当前标准API中,只关注了NOTIFY_STOP_MASK,其他的在notifier_call_chain中未做处理。
典型用例:
在linux中,液晶显示器会提供一个fb_notify,当显示器发生某种事件时,会调用notifier_call_chain,这样注册的回调函数得到执行,回调函数根据显示的framebuffer状态执行你预想的动作。
它选用通知链类型的是blocking_notifier_chain。
- /*
- * linux/drivers/video/fb_notify.c
- *
- * Copyright (C) 2006 Antonino Daplas <adaplas@pol.net>
- *
- * 2001 - Documented with DocBook
- * - Brad Douglas <brad@neruo.com>
- *
- * This file is subject to the terms and conditions of the GNU General Public
- * License. See the file COPYING in the main directory of this archive
- * for more details.
- */
- #include <linux/fb.h>
- #include <linux/notifier.h>
- #include <linux/export.h>
- /*静态定义并初始化通知链头*/
- static BLOCKING_NOTIFIER_HEAD(fb_notifier_list);
- /** 注册回调函数,加入一个回调函数节点
- * fb_register_client - register a client notifier
- * @nb: notifier block to callback on events
- */
- int fb_register_client(struct notifier_block *nb)
- {
- return blocking_notifier_chain_register(&fb_notifier_list, nb);
- }
- EXPORT_SYMBOL(fb_register_client);
- /** 注销回调函数,删除一个回调函数节点
- * fb_unregister_client - unregister a client notifier
- * @nb: notifier block to callback on events
- */
- int fb_unregister_client(struct notifier_block *nb)
- {
- return blocking_notifier_chain_unregister(&fb_notifier_list, nb);
- }
- EXPORT_SYMBOL(fb_unregister_client);
- /** 当源即framebuffer发生某种事件,调用该函数执行所有回调函数,通知其他子系统
- * fb_notifier_call_chain - notify clients of fb_events
- *
- */
- int fb_notifier_call_chain(unsigned long val, void *v)
- {
- return blocking_notifier_call_chain(&fb_notifier_list, val, v);
- }
- EXPORT_SYMBOL_GPL(fb_notifier_call_chain);
B子系统(触屏)/被通知者,代码如下:
- kernel\drivers\input\touchscreen\ft5x06_ts.c
- #if defined(CONFIG_FB)
- static int fb_notifier_callback(struct notifier_block *self,
- unsigned long event, void *data)
- {
- struct fb_event *evdata = data;
- int *blank;
- struct ft5x06_ts_data *ft5x06_data =
- container_of(self, struct ft5x06_ts_data, fb_notif);
- /* 检测是否是显示器BLANK改变事件 */
- if (evdata && evdata->data && event == FB_EVENT_BLANK &&
- ft5x06_data && ft5x06_data->client) {
- blank = evdata->data;
- if (*blank == FB_BLANK_UNBLANK) /*是BLANK事件中的LCD亮屏事件,唤醒触屏*/
- ft5x06_ts_resume(&ft5x06_data->client->dev);
- else if (*blank == FB_BLANK_POWERDOWN) /*是BLANK事件中的LCD灭屏事件,让触屏休眠 */
- ft5x06_ts_suspend(&ft5x06_data->client->dev);
- }
- return 0;
- }
- #elif defined(CONFIG_HAS_EARLYSUSPEND)
- //......
- #endif
- static int ft5x06_ts_probe(struct i2c_client *client,
- const struct i2c_device_id *id)
- {
- //......
- #if defined(CONFIG_FB)
- data->fb_notif.notifier_call = fb_notifier_callback;
- /*注册fb回调函数*/
- err = fb_register_client(&data->fb_notif);
- if (err)
- dev_err(&client->dev, "Unable to register fb_notifier: %d\n",
- err);
- #endif
- //......
- }
- static int __devexit ft5x06_ts_remove(struct i2c_client *client)
- {
- //......
- #if defined(CONFIG_FB)
- /*注销fb回调函数*/
- if (fb_unregister_client(&data->fb_notif))
- dev_err(&client->dev, "Error occurred while unregistering fb_notifier.\n");
- #elif defined(CONFIG_HAS_EARLYSUSPEND)
- unregister_early_suspend(&data->early_suspend);
- #endif
- //......
- }
A子系统(framebuffer)/通知者,代码如下:
- int fb_blank(struct fb_info *info, int blank)
- {
- int ret = -EINVAL;
- if (blank > FB_BLANK_POWERDOWN)
- blank = FB_BLANK_POWERDOWN;
- if (info->fbops->fb_blank) /*硬件执行亮屏还是灭屏的操作*/
- ret = info->fbops->fb_blank(blank, info);
- if (!ret) {
- struct fb_event event;
- event.info = info;
- event.data = ␣
- /*硬件BLANK操作成功后,调用所有的注册回调函数,比如通知给触屏*/
- fb_notifier_call_chain(FB_EVENT_BLANK, &event);
- }
- return ret;
- }
- /*fbmem中的ioctl*/
- static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
- unsigned long arg)
- {
- //.......
- case FBIOBLANK: //由上层发下来的亮屏还是息屏的IO命令
- if (!lock_fb_info(info))
- return -ENODEV;
- console_lock();
- info->flags |= FBINFO_MISC_USEREVENT;
- ret = fb_blank(info, arg);
- info->flags &= ~FBINFO_MISC_USEREVENT;
- console_unlock();
- unlock_fb_info(info);
- break;
- //......
- }
至于framebuffer中的notifier_call_chain的第二、三个参数,详见linux\fb.h,fbmem.c,fbcon.c。有时间也写个关于fb相关的文章。
通过上面所述,notifier_chain机制只能在内核个子系统间使用,因此,这里使用3个模块:test_notifier_chain_0、test_notifier_chain_1、test_notifier_chain_2;当 test_notifier_chain_2通过module_init初始化模块时发出事件TESTCHAIN_2_INIT;然后 test_notifier_chain_1作出相应的处理:打印 test_notifier_chain_2正在初始化。
- /* test_chain_0.c :0. 申明一个通知链;1. 向内核注册通知链;2. 定义事件; 3. 导出符号,因而必需最后退出*/
- #include <linux/notifier.h>
- #include <linux/module.h>
- #include <linux/init.h>
- #include <linux/kernel.h> /* printk() */
- #include <linux/fs.h> /* everything() */
- #define TESTCHAIN_INIT 0x52U
- static RAW_NOTIFIER_HEAD(test_chain);
- /* define our own notifier_call_chain */
- static int call_test_notifiers(unsigned long val, void *v)
- {
- return raw_notifier_call_chain(&test_chain, val, v);
- }
- EXPORT_SYMBOL(call_test_notifiers);
- /* define our own notifier_chain_register func */
- static int register_test_notifier(struct notifier_block *nb)
- {
- int err;
- err = raw_notifier_chain_register(&test_chain, nb);
- if(err)
- goto out;
- out:
- return err;
- }
- EXPORT_SYMBOL(register_test_notifier);
- static int __init test_chain_0_init(void)
- {
- printk(KERN_DEBUG "I'm in test_chain_0\n");
- return 0;
- }
- static void __exit test_chain_0_exit(void)
- {
- printk(KERN_DEBUG "Goodbye to test_chain_0\n");
- // call_test_notifiers(TESTCHAIN_EXIT, (int *)NULL);
- }
- MODULE_LICENSE("GPL v2");
- MODULE_AUTHOR("fishOnFly");
- module_init(test_chain_0_init);
- module_exit(test_chain_0_exit);
- /* test_chain_1.c :1. 定义回调函数;2. 定义notifier_block;3. 向chain_0注册notifier_block;*/
- #include <linux/notifier.h>
- #include <linux/module.h>
- #include <linux/init.h>
- #include <linux/kernel.h> /* printk() */
- #include <linux/fs.h> /* everything() */
- extern int register_test_notifier(struct notifier_block *nb);
- #define TESTCHAIN_INIT 0x52U
- /* realize the notifier_call func */
- int test_init_event(struct notifier_block *nb, unsigned long event,
- void *v)
- {
- switch(event){
- case TESTCHAIN_INIT:
- printk(KERN_DEBUG "I got the chain event: test_chain_2 is on the way of init\n");
- break;
- default:
- break;
- }
- return NOTIFY_DONE;
- }
- /* define a notifier_block */
- static struct notifier_block test_init_notifier = {
- .notifier_call = test_init_event,
- };
- static int __init test_chain_1_init(void)
- {
- printk(KERN_DEBUG "I'm in test_chain_1\n");
- register_test_notifier(&test_init_notifier);<span style="white-space:pre"> </span>// 由chain_0提供的设施
- return 0;
- }
- static void __exit test_chain_1_exit(void)
- {
- printk(KERN_DEBUG "Goodbye to test_clain_l\n");
- }
- MODULE_LICENSE("GPL");
- MODULE_AUTHOR("fishOnFly");
- module_init(test_chain_1_init);
- module_exit(test_chain_1_exit);
- /* test_chain_2.c:发出通知链事件*/
- #include <linux/notifier.h>
- #include <linux/module.h>
- #include <linux/init.h>
- #include <linux/kernel.h> /* printk() */
- #include <linux/fs.h> /* everything() */
- extern int call_test_notifiers(unsigned long val, void *v);
- #define TESTCHAIN_INIT 0x52U
- static int __init test_chain_2_init(void)
- {
- printk(KERN_DEBUG "I'm in test_chain_2\n");
- call_test_notifiers(TESTCHAIN_INIT, "no_use");
- return 0;
- }
- static void __exit test_chain_2_exit(void)
- {
- printk(KERN_DEBUG "Goodbye to test_chain_2\n");
- }
- MODULE_LICENSE("GPL v2");
- MODULE_AUTHOR("fishOnFly");
- module_init(test_chain_2_init);
- module_exit(test_chain_2_exit);
- # Makefile
- # Comment/uncomment the following line to disable/enable debugging
- # DEBUG = y
- # Add your debugging flag (or not) to CFLAGS
- ifeq ($(DEBUG),y)
- DEBFLAGS = -O -g -DSCULL_DEBUG # "-O" is needed to expand inlines
- else
- DEBFLAGS = -O2
- endif
- ifneq ($(KERNELRELEASE),)
- # call from kernel build system
- obj-m := test_chain_0.o test_chain_1.o test_chain_2.o
- else
- KERNELDIR ?= /lib/modules/$(shell uname -r)/build
- PWD := $(shell pwd)
- modules:
- $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
- endif
- clean:
- rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions
- depend .depend dep:
- $(CC) $(CFLAGS) -M *.c > .depend
- ifeq (.depend,$(wildcard .depend))
- include .depend
- endif
- [wang2@iwooing: notifier_chian]$ sudo insmod./test_chain_0.ko
- [wang2@iwooing: notifier_chian]$ sudo insmod./test_chain_1.ko
- [wang2@iwooing: notifier_chian]$ sudo insmod./test_chain_2.ko
- [wang2@iwooing: notifier_chian]$ dmesg
- [ 5950.112649] I'm in test_chain_0
- [ 5956.766610] I'm in test_chain_1
- [ 5962.570003] I'm in test_chain_2
- [ 5962.570008] I got the chain event: test_chain_2 is on the way of init
- [ 6464.042975] Goodbye to test_chain_2
- [ 6466.368030] Goodbye to test_clain_l
- [ 6468.371479] Goodbye to test_chain_0