同步、互斥、阻塞
目标:同一时刻只能有一个应用程序打开驱动程序。
- #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 atomic_t canopen = ATOMIC_INIT(1); //定义原子变量并初始化为1
- 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 0
- if (!atomic_dec_and_test(&canopen))
- {
- atomic_inc(&canopen);
- return -EBUSY;
- }
- #endif
- if (file->f_flags & O_NONBLOCK) // 阻塞
- {
- if (down_trylock(&button_lock)) // 如果获取不到信号量,则立即返回。
- return -EBUSY;
- }
- else // 非阻塞
- {
- /* 获取信号量 */
- down(&button_lock); // 第二次获取信号量时会进入休眠,第一个应用程序释放后才会被唤醒。
- }
- /* 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;
- if (file->f_flags & O_NONBLOCK) // 如果是阻塞
- {
- if (!ev_press) // 判断有无按键按下
- return -EAGAIN; // 没有按键按下再再次执行。
- }
- else // 阻塞
- {
- /* 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]);
- 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,指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");
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。
fd = open("...", O_RDWR | O_NONBLOCK);
- #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;
- //signal(SIGIO, my_signal_fun);
-
- fd = open("/dev/buttons", O_RDWR | O_NONBLOCK); // 非阻塞的方式打开
- 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)
- {
- ret = read(fd, &key_val, 1);
- printf("key_val: 0x%x, ret = %d\n", key_val, ret);
- sleep(5);
- }
-
- return 0;
- }
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