同步互斥阻塞
同步互斥阻塞
方法2：使用信号量：
目的：在同一时刻只允许一个应用程序打开/dev/***
下面试着在驱动中的open函数中加入：
static int canopen = 1;
if(--canopen!=0)
{
canopen++;
return -EBUSY;
}加入这段代码的意思在app调用open函数打开对应的设备后，最终调用底层驱动的open函数，在这个open函数中，如果canopen不为0的话就canopen++然后退出。如果为0，就继续下面的打开初始化动作。
这种方法会在多任务操作系统下出现问题：
因为--canopen解析成汇编有下面的三个步骤：
a.读出
b.修改
c.写回
linux是个多任务的系统，会在进行b操作之前a操作之后被另一个应用修改。可能导致多个应用程序打开同一设备的现象。
那么如何避免这种现象的发生呢？
方法1：原子操作，这样会将读出，修改，写回的过程一次性的完成，不会发生上面的情况。
方法2：信号量
信号量和原子操作的区别是，第2个应用程序操作同一个设备的时候会将第2个程序加入到队列中，第一个应用程序结束后，会继续执行第2个应用程序（第2个应用程序处于僵死状态）
原子操作：
原子操作指的是在执行过程中不会被别的代码路径所中断的操作。
常用原子操作函数举例：
atomic_t v = ATOMIC_INIT(0); //定义原子变量v并初始化为0
atomic_read(atomic_t *v); //返回原子变量的值
void atomic_inc(atomic_t *v); //原子变量增加1
void atomic_dec(atomic_t *v); //原子变量减少1
int atomic_dec_and_test(atomic_t *v); //自减操作后测试其是否为0，为0则返回true，否则返回false。
原子操作示例：
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/poll.h>
static struct class *sixthdrv_class;
static struct class_device *sixthdrv_class_dev;
//volatile unsigned long *gpfcon;
//volatile unsigned long *gpfdat;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
/* 中断事件标志, 中断服务程序将它置1，sixth_drv_read将它清0 */
static volatile int ev_press = 0;
static struct fasync_struct *button_async;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
/* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;
/*
* K1,K2,K3,K4对应GPF1、GPF4、GPF2、GPF0
*/
struct pin_desc pins_desc[4] = {
{S3C2410_GPF1, 0x01},
{S3C2410_GPF4, 0x02},
{S3C2410_GPF2, 0x03},
{S3C2410_GPF0, 0x04},
};
static atomic_t canopen = ATOMIC_INIT(1); //定义原子变量canopen并将其初始化为1
/*
* 确定按键值
*/
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
struct pin_desc * pindesc = (struct pin_desc *)dev_id;
unsigned int pinval;
pinval = s3c2410_gpio_getpin(pindesc->pin);
if (pinval)
{
/* 松开 */
key_val = 0x80 | pindesc->key_val;
}
else
{
/* 按下 */
key_val = pindesc->key_val;
}
ev_press = 1; /* 表示中断发生了 */
wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
kill_fasync (&button_async, SIGIO, POLL_IN);
return IRQ_RETVAL(IRQ_HANDLED);
}
static int sixth_drv_open(struct inode *inode, struct file *file)
{
if (!atomic_dec_and_test(&canopen))//自减操作后测试canopen是否为0，为0则返回true，否则返回false。
{
atomic_inc(&canopen);//做++操作
return -EBUSY;//返回BUSY状态
}
/* GPF1、GPF4、GPF2、GPF0为中断引脚 */
request_irq(IRQ_EINT1, buttons_irq, IRQT_BOTHEDGE, "K1", &pins_desc[0]);
request_irq(IRQ_EINT4, buttons_irq, IRQT_BOTHEDGE, "K2", &pins_desc[1]);
request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "K3", &pins_desc[2]);
request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "K4", &pins_desc[3]);
return 0;
}
ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
if (size != 1)
return -EINVAL;
/* 如果没有按键动作, 休眠 */
wait_event_interruptible(button_waitq, ev_press);
/* 如果有按键动作, 返回键值 */
copy_to_user(buf, &key_val, 1);
ev_press = 0;
return 1;
}
int sixth_drv_close(struct inode *inode, struct file *file)
{
atomic_inc(&canopen);//设备关闭后进行自加操作，返回canopen等于1的状态
free_irq(IRQ_EINT1, &pins_desc[0]);
free_irq(IRQ_EINT4, &pins_desc[1]);
free_irq(IRQ_EINT2, &pins_desc[2]);
free_irq(IRQ_EINT0, &pins_desc[3]);
return 0;
}
static unsigned sixth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait); // 不会立即休眠
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static int sixth_drv_fasync (int fd, struct file *filp, int on)
{
printk("driver: sixth_drv_fasync\n");
return fasync_helper (fd, filp, on, &button_async);
}
static struct file_operations sencod_drv_fops = {
.owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open = sixth_drv_open,
.read = sixth_drv_read,
.release = sixth_drv_close,
.poll = sixth_drv_poll,
.fasync = sixth_drv_fasync,
};
int major;
static int sixth_drv_init(void)
{
major = register_chrdev(0, "sixth_drv", &sencod_drv_fops);
sixthdrv_class = class_create(THIS_MODULE, "sixth_drv");
sixthdrv_class_dev = class_device_create(sixthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */
// gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
// gpfdat = gpfcon + 1;
return 0;
}
static void sixth_drv_exit(void)
{
unregister_chrdev(major, "sixth_drv");
class_device_unregister(sixthdrv_class_dev);
class_destroy(sixthdrv_class);
// iounmap(gpfcon);
return 0;
}
module_init(sixth_drv_init);
module_exit(sixth_drv_exit);
MODULE_LICENSE("GPL");
方法2：使用信号量：
信号量（semaphore）是用于保护临界区的一种常用方法，只有得到信号量的进程才能执行临界区代码。当获取不到信号量时，进程进入休眠等待状态（这就是和原子操作的区别，原子操作如果当前被别的应用程序使用的话，就会立刻返回）。
定义信号量
struct semaphore sem;
初始化信号量
void sema_init (struct semaphore *sem, int val);//初始化信号量sem并设置它的值为val
void init_MUTEX(struct semaphore *sem);//初始化信号量并设置它为0
或者直接使用
static DECLARE_MUTEX(button_lock); //定义互斥锁
获得信号量
void down(struct semaphore * sem);
int down_interruptible(struct semaphore * sem);//试着去获取信号量，获取不了则休眠，但是会被中断打断
int down_trylock(struct semaphore * sem);//试着去获取信号量，如果获取不了就立刻返回
释放信号量
void up(struct semaphore * sem);
例子：
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/poll.h>
static struct class *sixthdrv_class;
static struct class_device *sixthdrv_class_dev;
//volatile unsigned long *gpfcon;
//volatile unsigned long *gpfdat;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
/* 中断事件标志, 中断服务程序将它置1，sixth_drv_read将它清0 */
static volatile int ev_press = 0;
static struct fasync_struct *button_async;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
/* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;
/*
* K1,K2,K3,K4对应GPF1、GPF4、GPF2、GPF0
*/
struct pin_desc pins_desc[4] = {
{S3C2410_GPF1, 0x01},
{S3C2410_GPF4, 0x02},
{S3C2410_GPF2, 0x03},
{S3C2410_GPF0, 0x04},
};
static DECLARE_MUTEX(button_lock); //定义互斥锁，并初始化它
/*
* 确定按键值
*/
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
struct pin_desc * pindesc = (struct pin_desc *)dev_id;
unsigned int pinval;
pinval = s3c2410_gpio_getpin(pindesc->pin);
if (pinval)
{
/* 松开 */
key_val = 0x80 | pindesc->key_val;
}
else
{
/* 按下 */
key_val = pindesc->key_val;
}
ev_press = 1; /* 表示中断发生了 */
wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
kill_fasync (&button_async, SIGIO, POLL_IN);
return IRQ_RETVAL(IRQ_HANDLED);
}
static int sixth_drv_open(struct inode *inode, struct file *file)
{
/* 获取信号量 每个应用程序打开一个设备就会获取信号量，这样别的app打开的时候就会进入休眠状态*/
down(&button_lock);
/* GPF1、GPF4、GPF2、GPF0为中断引脚 */
request_irq(IRQ_EINT1, buttons_irq, IRQT_BOTHEDGE, "K1", &pins_desc[0]);
request_irq(IRQ_EINT4, buttons_irq, IRQT_BOTHEDGE, "K2", &pins_desc[1]);
request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "K3", &pins_desc[2]);
request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "K4", &pins_desc[3]);
return 0;
}
ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
if (size != 1)
return -EINVAL;
/* 如果没有按键动作, 休眠 */
wait_event_interruptible(button_waitq, ev_press);
/* 如果有按键动作, 返回键值 */
copy_to_user(buf, &key_val, 1);
ev_press = 0;
return 1;
}
int sixth_drv_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT1, &pins_desc[0]);
free_irq(IRQ_EINT4, &pins_desc[1]);
free_irq(IRQ_EINT2, &pins_desc[2]);
free_irq(IRQ_EINT0, &pins_desc[3]);
up(&button_lock);//在第一个应用程序关闭设备的时候，一定要释放信号量，从而使第2个应用程序可以打开它
return 0;
}
static unsigned sixth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait); // 不会立即休眠
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static int sixth_drv_fasync (int fd, struct file *filp, int on)
{
printk("driver: sixth_drv_fasync\n");
return fasync_helper (fd, filp, on, &button_async);
}
static struct file_operations sencod_drv_fops = {
.owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open = sixth_drv_open,
.read = sixth_drv_read,
.release = sixth_drv_close,
.poll = sixth_drv_poll,
.fasync = sixth_drv_fasync,
};
int major;
static int sixth_drv_init(void)
{
major = register_chrdev(0, "sixth_drv", &sencod_drv_fops);
sixthdrv_class = class_create(THIS_MODULE, "sixth_drv");
sixthdrv_class_dev = class_device_create(sixthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */
// gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
// gpfdat = gpfcon + 1;
return 0;
}
static void sixth_drv_exit(void)
{
unregister_chrdev(major, "sixth_drv");
class_device_unregister(sixthdrv_class_dev);
class_destroy(sixthdrv_class);
// iounmap(gpfcon);
return 0;
}
module_init(sixth_drv_init);
module_exit(sixth_drv_exit);
MODULE_LICENSE("GPL");阻塞：
比如：读取一个按键值，如果当前没有读取到的话继续去读，表示阻塞，如果没有读到立即返回的话，就表示非阻塞
那么如何区分阻塞和非阻塞呢？
在应用程序中的open函数中加入O_NONBLOCK标志的话就表示非阻塞操作，没有这个标志的话，默认的情况是阻塞的操作如下所示：
fd = open("...", O_RDWR | O_NONBLOCK);
在驱动中是通过：
file->f_flags & O_NONBLOCK
来判断是否是阻塞操作的。
下面看下例子：
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/poll.h>
static struct class *sixthdrv_class;
static struct class_device *sixthdrv_class_dev;
//volatile unsigned long *gpfcon;
//volatile unsigned long *gpfdat;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
/* 中断事件标志, 中断服务程序将它置1，sixth_drv_read将它清0 */
static volatile int ev_press = 0;
static struct fasync_struct *button_async;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
/* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;
/*
* K1,K2,K3,K4对应GPF1、GPF4、GPF2、GPF0
*/
struct pin_desc pins_desc[4] = {
{S3C2410_GPF1, 0x01},
{S3C2410_GPF4, 0x02},
{S3C2410_GPF2, 0x03},
{S3C2410_GPF0, 0x04},
};
static DECLARE_MUTEX(button_lock); //定义互斥锁
/*
* 确定按键值
*/
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
struct pin_desc * pindesc = (struct pin_desc *)dev_id;
unsigned int pinval;
pinval = s3c2410_gpio_getpin(pindesc->pin);
if (pinval)
{
/* 松开 */
key_val = 0x80 | pindesc->key_val;
}
else
{
/* 按下 */
key_val = pindesc->key_val;
}
ev_press = 1; /* 表示中断发生了 */
wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
kill_fasync (&button_async, SIGIO, POLL_IN);
return IRQ_RETVAL(IRQ_HANDLED);
}
static int sixth_drv_open(struct inode *inode, struct file *file)
{
if (file->f_flags & O_NONBLOCK)//根据file->f_flags来判断是否在应用程序中设置了O_NONBLOCK标志，如果设置了则进行里面的动作
{
if (down_trylock(&button_lock))//试着去获取信号量，如果没有获取到，则返回BUSY状态
return -EBUSY;
}
else
{
/* 获取信号量 */
down(&button_lock);//如果app中没有设置O_NONBLOCK标志，则开始获取信号量，进入阻塞状态
}
/* GPF1、GPF4、GPF2、GPF0为中断引脚 */
request_irq(IRQ_EINT1, buttons_irq, IRQT_BOTHEDGE, "K1", &pins_desc[0]);
request_irq(IRQ_EINT4, buttons_irq, IRQT_BOTHEDGE, "K2", &pins_desc[1]);
request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "K3", &pins_desc[2]);
request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "K4", &pins_desc[3]);
return 0;
}
ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
if (size != 1)
return -EINVAL;
if (file->f_flags & O_NONBLOCK)//读操作也是一样，如果设置了非阻塞然后判断按键是否按下，没有按下立刻返回AGAIN的错误信息
{
if (!ev_press)
return -EAGAIN;
}
else
{
/* 如果没有按键动作, 休眠 */
wait_event_interruptible(button_waitq, ev_press);//设置阻塞的情况，则进入休眠
}
/* 如果有按键动作, 返回键值 */
copy_to_user(buf, &key_val, 1);
ev_press = 0;
return 1;
}
int sixth_drv_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT1, &pins_desc[0]);
free_irq(IRQ_EINT4, &pins_desc[1]);
free_irq(IRQ_EINT2, &pins_desc[2]);
free_irq(IRQ_EINT0, &pins_desc[3]);
up(&button_lock);
return 0;
}
static unsigned sixth_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait); // 不会立即休眠
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static int sixth_drv_fasync (int fd, struct file *filp, int on)
{
printk("driver: sixth_drv_fasync\n");
return fasync_helper (fd, filp, on, &button_async);
}
static struct file_operations sencod_drv_fops = {
.owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open = sixth_drv_open,
.read = sixth_drv_read,
.release = sixth_drv_close,
.poll = sixth_drv_poll,
.fasync = sixth_drv_fasync,
};
int major;
static int sixth_drv_init(void)
{
major = register_chrdev(0, "sixth_drv", &sencod_drv_fops);
sixthdrv_class = class_create(THIS_MODULE, "sixth_drv");
sixthdrv_class_dev = class_device_create(sixthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */
// gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
// gpfdat = gpfcon + 1;
return 0;
}
static void sixth_drv_exit(void)
{
unregister_chrdev(major, "sixth_drv");
class_device_unregister(sixthdrv_class_dev);
class_destroy(sixthdrv_class);
// iounmap(gpfcon);
return 0;
}
module_init(sixth_drv_init);
module_exit(sixth_drv_exit);
MODULE_LICENSE("GPL");