x4412&ibox项目实战35－使用信号量避免并发竞争 - 九鼎创展论坛

struct semaphore sem;

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void sema_init (struct semaphore *sem, int val);

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void init _ MUTEX(struct semaphore *sem);

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sema_init (struct semaphore *sem, 1)。

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void init _ MUTEX _ LOCKED (struct semaphore *sem);

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sema_init (struct semaphore *sem, 0)。

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DEFINE_SEMAPHORE (name)

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void down(struct semaphore * sem);

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int down_interruptible(struct semaphore * sem);

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int down_trylock(struct semaphore * sem);

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if (down _ interruptible(&sem))
{
return - ERESTARTSYS;
}

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void up(struct semaphore * sem);

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//定义信号量
DECLARE _ MUTEX(mount _ sem);
down(&mount _ sem);//获取信号量，保护临界区
...
critical section //临界区
...
up(&mount _ sem);//释放信号量

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#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include <linux/device.h>
static int x4412_semaphore_major;
static struct cdev x4412_semaphore;
static struct class *cdev_class;
DEFINE_SEMAPHORE(sem_lock);
int x4412_semaphore_open(struct inode *inode, struct file *filp)
{
int ret;
if(down_trylock(&sem_lock))
{
printk("x4412-semaphore open error.\r\n");
return -EBUSY;
}
return 0;
}
int x4412_semaphore_release(struct inode *inode, struct file *filp)
{
printk("x4412-semaphore close.\r\n");
up(&sem_lock);
return 0;
}
static const struct file_operations x4412_fops =
{
.owner = THIS_MODULE,
.open = x4412_semaphore_open,
.release = x4412_semaphore_release,
};
static void x4412_setup_cdev(void)
{
int err, devno = MKDEV(x4412_semaphore_major, 0);
cdev_init(&x4412_semaphore, &x4412_fops);
err = cdev_add(&x4412_semaphore, devno, 1);
if (err)
printk(KERN_NOTICE "Error %d adding x4412_semaphore", err);
}
static void x4412_clear_cdev(void)
{
cdev_del(&x4412_semaphore);
unregister_chrdev_region(MKDEV(x4412_semaphore_major, 0), 1);
}
int x4412_semaphore_init(void)
{
int result;
dev_t devno;
result = alloc_chrdev_region(&devno, 0, 1, "x4412-semaphore");
x4412_semaphore_major = MAJOR(devno);
if(result < 0)
{
printk("register x4412-semaphore error!\r\n");
return result;
}
x4412_setup_cdev();
cdev_class = class_create(THIS_MODULE,"x4412-semaphore");
if(IS_ERR(cdev_class))
{
x4412_clear_cdev();
return PTR_ERR(cdev_class);
}
device_create(cdev_class,NULL,MKDEV(x4412_semaphore_major,0),NULL,"x4412-semaphore");
return 0;
}
void x4412_semaphore_exit(void)
{
device_destroy(cdev_class,MKDEV(x4412_semaphore_major,0));
class_destroy(cdev_class);
x4412_clear_cdev();
}
MODULE_AUTHOR("www.9tripod.com");
MODULE_LICENSE("GPL");
module_init(x4412_semaphore_init);
module_exit(x4412_semaphore_exit);

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config X4412_SEMAPHORE_DRIVER
tristate "x4412 semaphore driver"
default m
help
compile for x4412 semaphore driver,y for kernel,m for module.

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obj-$(CONFIG_X4412_SEMAPHORE_DRIVER) += x4412-semaphore.o

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#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#define DEVICE_NAME "/dev/x4412-semaphore"
#define SEM_DEBUG
int main(int argc,char **argv)
{
int fd;
fd = open(DEVICE_NAME,O_RDWR);
if(fd < 0)
{
printf("open device %s error \n",DEVICE_NAME);
}
else
{
#ifdef SEM_DEBUG
fd = open(DEVICE_NAME,O_RDWR);
if(fd < 0)
{
printf("repeat open device %s error!\r\n",DEVICE_NAME);
}
usleep(5000);
#endif
close(fd);
}
return 0;
}

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arm-none-linux-gnueabi-gcc x4412-semaphore-app.c -o x4412-semaphore-app

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[root@x4412 mnt]# insmod x4412-semaphore.ko
[root@x4412 mnt]# ./x4412-semaphore-app
[ 1385.583258] x4412-semaphore open error.
repeat open device /dev/x4412-semaphore error!
[ 1385.591150] x4412-semaphore close.

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