04lock_02atomic

#include <linux/module.h>  //MODULE_LICENSE("GPL"); 
#include <linux/init.h>   //module_init  module_exit
#include <linux/kernel.h>  //printk
#include <linux/io.h>    //ioremap  iounremap
#include <linux/ioport.h>  //request_mem_region


#include <linux/miscdevice.h>
#include <linux/fs.h>   //file_operations  结构体的定义
#include <linux/slab.h>  //kmalloc
#include <linux/delay.h>

#include <asm/uaccess.h>    //copy_to_user  copy_form_user
#include <asm/atomic.h>  

/*
该设备只能同时被一个进程打开
*/


#define   DEVNAME  "my_led"
#define  MEMSIZE  100

struct ldm_info
{
    struct  miscdevice dev;       //设备节点
    struct  file_operations  ops;  //文件操作
    unsigned char mem[MEMSIZE] ;  //数组, 内核的空间
    atomic_t   atomic; //原子变量,用于防止多个进程同时打开
};

//struct ldm_info  ldm;
struct ldm_info  ldm;  //结构体的指针,分配空间

static  int ldm_open(struct inode * inode, struct file * file)
{
    printk("kernel: ldm_open
");
    //先自减  test
    if(!atomic_dec_and_test(&ldm.atomic)) {
        atomic_inc(&ldm.atomic);
        return -1;
    }

    return 0;
}

/*
copy_to_user
copy_form_user
*/

static  ssize_t ldm_write(struct file * file, const char __user * buf, size_t size, loff_t *   offt)
{
    int i =0;
    for(;i < size; i++) {
        //每拷贝一个字节,睡眠1s
        copy_from_user(ldm.mem + i, buf + i, 1);
        printk("write:%c
",  ldm.mem[i]);
        ssleep(1); //延迟1s
    }

    return 0;
}


ssize_t ldm_read(struct file * file, char __user *  buf, size_t size, loff_t * offt)
{
    //每隔一秒拷贝一个字节到用户层
    int i =0;
    for(;i < size; i++) {
        //每拷贝一个字节,睡眠1s
        copy_to_user(buf + i, ldm.mem + i, 1);
        printk("read:%c
",  ldm.mem[i]);
        ssleep(1); //延迟1s
    }

    return 0;
}

int ldm_release(struct inode * inode, struct file *file)
{
    printk("kernel: close
");
    atomic_inc(&ldm.atomic);  //+1
    return 0;
}

static int test_init(void)
{
    int ret = 0;

    printk("%s:%s:%d   init
", __FILE__, __FUNCTION__, __LINE__);


    ldm.dev.minor  = MISC_DYNAMIC_MINOR;  //系统自动分配次设备
    ldm.dev.name = DEVNAME;//该名称将决定节点名称, 成功注册 linux 系统中
    ldm.dev.fops = &ldm.ops;  //关联文件操作
    ldm.ops.open = ldm_open;
    ldm.ops.write = ldm_write;
    ldm.ops.read = ldm_read;
    ldm.ops.release = ldm_release;


    ret = misc_register(&ldm.dev);

    //原子变量 初始化为1
    atomic_set(&ldm.atomic, 1);

    if(ret < 0) {
        printk("misc_register  failed
");
        goto  err_misc_register;
    }

    return 0;
err_misc_register:
    return ret;

}

//卸载
static void test_exit(void)
{
    printk("%s:%s:%d   init
", __FILE__, __FUNCTION__, __LINE__);


    //注销misc 
    misc_deregister(&ldm.dev);
    //释放映射的虚拟地址

}

module_init(test_init);
module_exit(test_exit);


MODULE_LICENSE("GPL");  //加入GPL许可