一、同步互斥阻塞
1. 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。
2. 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。
定义信号量
struct semaphore sem;
初始化信号量
void sema_init (struct semaphore *sem, int val);
void init_MUTEX(struct semaphore *sem);//初始化为0
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);
int down_trylock(struct semaphore * sem);
释放信号量
void up(struct semaphore * sem);
3. 阻塞
阻塞操作
是指在执行设备操作时若不能获得资源则挂起进程，直到满足可操作的条件后再进行操作。
被挂起的进程进入休眠状态，被从调度器的运行队列移走，直到等待的条件被满足。
非阻塞操作
进程在不能进行设备操作时并不挂起，它或者放弃，或者不停地查询，直至可以进行操作为止。
默认阻塞
fd = open("...", O_RDWR | O_NONBLOCK);
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二、原子操作
1.
#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 *fifthdrv_class; static struct class_device *fifthdrv_class_dev;volatile unsigned long *gpfcon; volatile unsigned long *gpfdat;volatile unsigned long *gpgcon; volatile unsigned long *gpgdat;static DECLARE_WAIT_QUEUE_HEAD(button_waitq);/* 中断事件标志, 中断服务程序将它置1，fifth_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;struct pin_desc pins_desc[4] = {{S3C2410_GPF0, 0x01},{S3C2410_GPF2, 0x02},{S3C2410_GPG3, 0x03},{S3C2410_GPG11, 0x04}, };static atomic_t canopen = ATOMIC_INIT(1); //定义原子变量并初始化为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 fifth_drv_open(struct inode *inode, struct file *file) {if (!atomic_dec_and_test(&canopen)){atomic_inc(&canopen);return -EBUSY;}/* 配置GPF0,2为输入引脚 *//* 配置GPG3,11为输入引脚 */request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]); return 0; }ssize_t fifth_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 fifth_drv_close(struct inode *inode, struct file *file) {//释放掉atomic_inc(&canopen);free_irq(IRQ_EINT0, &pins_desc[0]);free_irq(IRQ_EINT2, &pins_desc[1]);free_irq(IRQ_EINT11, &pins_desc[2]);free_irq(IRQ_EINT19, &pins_desc[3]);return 0; }static unsigned fifth_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 fifth_drv_fasync (int fd, struct file *filp, int on) {printk("driver: fifth_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 = fifth_drv_open, .read = fifth_drv_read, .release = fifth_drv_close,.poll = fifth_drv_poll,.fasync = fifth_drv_fasync, };int major; static int fifth_drv_init(void) {major = register_chrdev(0, "fifth_drv", &sencod_drv_fops);fifthdrv_class = class_create(THIS_MODULE, "fifth_drv");fifthdrv_class_dev = class_device_create(fifthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);gpfdat = gpfcon + 1;gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);gpgdat = gpgcon + 1;return 0; }static void fifth_drv_exit(void) {unregister_chrdev(major, "fifth_drv");class_device_unregister(fifthdrv_class_dev);class_destroy(fifthdrv_class);iounmap(gpfcon);iounmap(gpgcon);return 0; }module_init(fifth_drv_init);module_exit(fifth_drv_exit);MODULE_LICENSE("GPL");
2.测试程序
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <poll.h> #include <signal.h> #include <sys/types.h> #include <unistd.h> #include <fcntl.h>int fd;void my_signal_fun(int signum) {unsigned char key_val;read(fd, &key_val, 1);printf("key_val: 0x%x\n", key_val); }int main(int argc, char **argv) {unsigned char key_val;int ret;int Oflags;signal(SIGIO, my_signal_fun);fd = open("/dev/buttons", O_RDWR);if (fd < 0){printf("can't open!\n");return -1;}fcntl(fd, F_SETOWN, getpid());Oflags = fcntl(fd, F_GETFL); fcntl(fd, F_SETFL, Oflags | FASYNC);while (1){sleep(1000);}return 0; }
三、信号量和阻塞
1.
#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;volatile unsigned long *gpgcon; volatile unsigned long *gpgdat;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;struct pin_desc pins_desc[4] = {{S3C2410_GPF0, 0x01},{S3C2410_GPF2, 0x02},{S3C2410_GPG3, 0x03},{S3C2410_GPG11, 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) { //如果非阻塞if (file->f_flags & O_NONBLOCK){if (down_trylock(&button_lock))return -EBUSY;}else{/* 获取信号量 *///如果无法获取信号量，则会休眠down(&button_lock);}/* 配置GPF0,2为输入引脚 *//* 配置GPG3,11为输入引脚 */request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &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;//非阻塞if (file->f_flags & O_NONBLOCK){if (!ev_press)return -EAGAIN;}//阻塞else{/* 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);free_irq(IRQ_EINT0, &pins_desc[0]);free_irq(IRQ_EINT2, &pins_desc[1]);free_irq(IRQ_EINT11, &pins_desc[2]);free_irq(IRQ_EINT19, &pins_desc[3]);
//释放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;gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);gpgdat = gpgcon + 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);iounmap(gpgcon);return 0; }module_init(sixth_drv_init);module_exit(sixth_drv_exit);MODULE_LICENSE("GPL");
2.测试程序
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <poll.h> #include <signal.h> #include <sys/types.h> #include <unistd.h> #include <fcntl.h>/* sixthdrvtest */ int fd;void my_signal_fun(int signum) {unsigned char key_val;read(fd, &key_val, 1);printf("key_val: 0x%x\n", key_val); }int main(int argc, char **argv) {unsigned char key_val;int ret;int Oflags;fd = open("/dev/buttons", O_RDWR | O_NONBLOCK); // fd = open("/dev/buttons", O_RDWR);//默认阻塞if (fd < 0){printf("can't open!\n");return -1;}while (1){ret = read(fd, &key_val, 1);printf("key_val: 0x%x, ret = %d\n", key_val, ret);sleep(5);}return 0; }