读者－写者实现

/*
 * Reader-Writer是指保证一个Writer进程必须与其他进程互斥地访问共享对象的同步问题
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sem.h>

struct semaphore sem_r;
struct semaphore sem_w;

int readcount = 0;        /*表示正在读的进程数(可改成大于0的数)*/

int Read_thread(void *p);
int Write_thread(void *p);

int Read_thread(void *p)
{
    p = p;
    down(&sem_r);        //使用读信号量

    if(readcount == 0)    //没有进程在读

        down(&sem_w);    //使用写信号量

    readcount += 1;
    up(&sem_r);        //释放读信号量

    
    printk("Lan is reading: %d\n", readcount);
    
    down(&sem_r);
    readcount -= 1;
    printk("Read Finish\n\n");
    if(readcount == 0)
        up(&sem_w);
    up(&sem_r);
    return 0;
}

int Write_thread(void *p)
{
    p = p;
    down(&sem_w);
    printk("Lan is writing\n");
    printk("Write Finish\n\n");
    up(&sem_w);
    return 0;
}

static int lan_init(void)
{
    printk("I am Coming\n");
    init_MUTEX(&sem_r);
    init_MUTEX(&sem_w);
    kernel_thread(Write_thread, NULL, CLONE_KERNEL);
    kernel_thread(Read_thread, NULL, CLONE_KERNEL);
    kernel_thread(Write_thread, NULL, CLONE_KERNEL);
    return 0;
}

static void lan_exit(void)
{
    printk("Bye Bye\n");
}

module_init(lan_init);
module_exit(lan_exit);

MODULE_LICENSE("GPL");

#vim Makefile

obj-m += duxie.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean
注意：两个make前要先使用Tab键空出。

#sudo insmod duxie.ko

#dmesg

最后几行显示：

I am Coming

Lan is writing

Write Finish

Lan is reading: 1

Read Finish

Lan is writing

Write Finish