04lock_02atomic

  1 #include <linux/module.h>  //MODULE_LICENSE("GPL"); 
  2 #include <linux/init.h>   //module_init  module_exit
  3 #include <linux/kernel.h>  //printk
  4 #include <linux/io.h>    //ioremap  iounremap
  5 #include <linux/ioport.h>  //request_mem_region
  6 
  7 
  8 #include <linux/miscdevice.h>
  9 #include <linux/fs.h>   //file_operations  结构体的定义
 10 #include <linux/slab.h>  //kmalloc
 11 #include <linux/delay.h>
 12 
 13 #include <asm/uaccess.h>    //copy_to_user  copy_form_user
 14 #include <asm/atomic.h>  
 15 
 16 /*
 17 该设备只能同时被一个进程打开
 18 */
 19 
 20 
 21 #define   DEVNAME  "my_led"
 22 #define  MEMSIZE  100
 23 
 24 struct ldm_info
 25 {
 26     struct  miscdevice dev;       //设备节点
 27     struct  file_operations  ops;  //文件操作
 28     unsigned char mem[MEMSIZE] ;  //数组, 内核的空间
 29     atomic_t   atomic; //原子变量,用于防止多个进程同时打开
 30 };
 31 
 32 //struct ldm_info  ldm;
 33 struct ldm_info  ldm;  //结构体的指针,分配空间
 34 
 35 static  int ldm_open(struct inode * inode, struct file * file)
 36 {
 37     printk("kernel: ldm_open
");
 38     //先自减  test
 39     if(!atomic_dec_and_test(&ldm.atomic)) {
 40         atomic_inc(&ldm.atomic);
 41         return -1;
 42     }
 43 
 44     return 0;
 45 }
 46 
 47 /*
 48 copy_to_user
 49 copy_form_user
 50 */
 51 
 52 static  ssize_t ldm_write(struct file * file, const char __user * buf, size_t size, loff_t *   offt)
 53 {
 54     int i =0;
 55     for(;i < size; i++) {
 56         //每拷贝一个字节,睡眠1s
 57         copy_from_user(ldm.mem + i, buf + i, 1);
 58         printk("write:%c
",  ldm.mem[i]);
 59         ssleep(1); //延迟1s
 60     }
 61 
 62     return 0;
 63 }
 64 
 65 
 66 ssize_t ldm_read(struct file * file, char __user *  buf, size_t size, loff_t * offt)
 67 {
 68     //每隔一秒拷贝一个字节到用户层
 69     int i =0;
 70     for(;i < size; i++) {
 71         //每拷贝一个字节,睡眠1s
 72         copy_to_user(buf + i, ldm.mem + i, 1);
 73         printk("read:%c
",  ldm.mem[i]);
 74         ssleep(1); //延迟1s
 75     }
 76 
 77     return 0;
 78 }
 79 
 80 int ldm_release(struct inode * inode, struct file *file)
 81 {
 82     printk("kernel: close
");
 83     atomic_inc(&ldm.atomic);  //+1
 84     return 0;
 85 }
 86 
 87 static int test_init(void)
 88 {
 89     int ret = 0;
 90 
 91     printk("%s:%s:%d   init
", __FILE__, __FUNCTION__, __LINE__);
 92 
 93 
 94     ldm.dev.minor  = MISC_DYNAMIC_MINOR;  //系统自动分配次设备
 95     ldm.dev.name = DEVNAME;//该名称将决定节点名称, 成功注册 linux 系统中
 96     ldm.dev.fops = &ldm.ops;  //关联文件操作
 97     ldm.ops.open = ldm_open;
 98     ldm.ops.write = ldm_write;
 99     ldm.ops.read = ldm_read;
100     ldm.ops.release = ldm_release;
101 
102 
103     ret = misc_register(&ldm.dev);
104 
105     //原子变量 初始化为1
106     atomic_set(&ldm.atomic, 1);
107 
108     if(ret < 0) {
109         printk("misc_register  failed
");
110         goto  err_misc_register;
111     }
112 
113     return 0;
114 err_misc_register:
115     return ret;
116 
117 }
118 
119 //卸载
120 static void test_exit(void)
121 {
122     printk("%s:%s:%d   init
", __FILE__, __FUNCTION__, __LINE__);
123 
124 
125     //注销misc 
126     misc_deregister(&ldm.dev);
127     //释放映射的虚拟地址
128 
129 }
130 
131 module_init(test_init);
132 module_exit(test_exit);
133 
134 
135 MODULE_LICENSE("GPL");  //加入GPL许可