1 #include <linux/init.h>
2 #include <linux/kernel.h>
3 #include <linux/module.h>
4 #include <linux/types.h>
5 #include <linux/fs.h>
6 #include <linux/errno.h>
7 #include <linux/mm.h>
8 #include <linux/sched.h>
9 #include <linux/cdev.h>
10 #include <linux/slab.h>
11 #include <asm/io.h>
12 #include <asm/uaccess.h>
13 #include <asm/system.h>
14 #include "memdev.h"//在头文件中定义了MEMDEV_SIZE=256，MEMDEV_NR=2,MEM_MAJOR=251;
15
16
17 int mem_major = MEM_MAJOR;
18
19 module_param(mem_major, int , S_IWUSR);//用mem_major作为内核参数，随时可以改变设备号
20
21 struct cdev cdev;
22 struct memdev *memdevp;
23 dev_t dev_no;
24
25 /*函数打开时调用*/
26 int mem_open(struct inode *inode, struct file *file)
27 {
28 struct memdev *memdev;
29 int i = MINOR(inode->i_rdev);
30 if(i > MEMDEV_NR)
31 return -EFAULT;
32 memdev = &memdevp[i];
33
34 file->private_data = memdev;//将设备指针保存在private_data里面，方便以后读写时取用;
35 return 0;
36
37 }
38
39 int mem_release(struct inode *inode, struct file *file)
40 {
41 return 0;
42 }
43 /*读文件时调用该函数*/
44 ssize_t mem_read(struct file *file, char __user *buffer, size_t size, loff_t *pos)
45 {
46 struct memdev *memdev;
47 int count = size;
48 int p = *pos;
49 int ret = 0;
50
51 if(p > MEMDEV_SIZE)
52 return -EFAULT;
53 if(count > MEMDEV_SIZE - p)
54 count = MEMDEV_SIZE -p;
55
56 memdev = file->private_data;
57 ret = copy_to_user(buffer, memdev->data + p, count);//在内核空间中不能直接使用用户空间的指针。
58
59 if(ret)
60 return -ENOMEM;
61 else{
62 *pos += count;
63 ret = count;
64 }
65
66 return ret;
67 }
68 /*写文件的时候调用该函数*/
69 ssize_t mem_write(struct file *file, const char __user *buffer, size_t size, loff_t *pos)
70 {
71 struct memdev *memdev;
72 int count = size;
73 int p = *pos;
74 int ret = 0;
75
76 if(p > MEMDEV_SIZE)
77 return -EFAULT;
78 if(count > MEMDEV_SIZE - p)
79 count = MEMDEV_SIZE - p;
80
81 memdev = file->private_data;//取出打开时，保存在private_data中的memdev指针；
82 ret = copy_from_user(memdev->data + p , buffer, count);//用户空间指针，不能直接在内核空间使用;
83
84 if(ret)
85 return -ENOMEM;
86 else{
87 *pos += count;//更新文件读写指针位置；
88 ret = count;
89 }
90
91 return ret;
92 }
93
94 loff_t mem_llseek(struct file *file, loff_t off, int whence)
95 {
96 loff_t newpos=0;
97
98 switch(whence){
99 case 0://seek_set
100 newpos = off;
101 break;
102 case 1://seek_cur
103 newpos = file->f_pos + off; //file_pos是文件原来的读写指针位置;
104 break;
105 case 2://seek_end
106 newpos = MEMDEV_SIZE -1 + off;
107 break;
108 default:
109 return -EFAULT;
110 }
111
112 file->f_pos = newpos;//更新文件读写指针位置;
113 return newpos;
114 }
115
116 /*定义一个mem_fops变量，并初始化它*/
117 struct file_operations mem_fops = {
118 .owner = THIS_MODULE,//此语句必须;
119 .open = mem_open,
120 .llseek = mem_llseek,
121 .read = mem_read,
122 .write = mem_write,
123 .release = mem_release,
124 };
125
126
127 static int __init memdev_init(void)
128 {
129 dev_no = MKDEV(mem_major, 0);
130 int result = 0;
131 int i=0;
132
133 if(mem_major){
134 result = register_chrdev_region(dev_no, MEMDEV_NR ,"memdev0");//当mem_major大于0的时候，使用静态分配设备号方式;
135 }else{
136 result = alloc_chrdev_region(&dev_no, 0 ,MEMDEV_NR,"memdev0");//当mem_major为0的时候，选用动态分配设备号的方式
137 mem_major = MAJOR(dev_no);
138 }
139
140 if(result != 0)
141 return -ENOMEM;
142
143 cdev_init(&cdev, &mem_fops);//使用mem_fops初始化设备结构cdev;
144 cdev.owner = THIS_MODULE;//制定该设备结构的拥有者为THIS_MODULE；
145
146 cdev_add(&cdev,dev_no,MEMDEV_NR);//使用设备号，以及设备结构，向内核注册设备;
147
148 memdevp = kmalloc(MEMDEV_NR * sizeof(struct memdev), GFP_KERNEL);//为虚拟的设备结构分配空间
149 if(!memdevp)
150 goto fail_malloc;
151 memset(memdevp , 0, MEMDEV_NR * sizeof(struct memdev));//初始化为0；
152
153 for(i = 0; i < MEMDEV_NR; i++){
154 memdevp[i].size = MEMDEV_SIZE;
155 memdevp[i].data = kmalloc(MEMDEV_SIZE ,GFP_KERNEL);//为虚拟设备结构中的数据部分分配空间;
156 if(!(memdevp[i].data)){
157 goto fail_malloc;
158 }
159 memset(memdevp[i].data , 0, MEMDEV_SIZE);
160 }
161
162 return 0;
163 fail_malloc:
164 unregister_chrdev_region(dev_no, MEMDEV_NR);//当出错的时候，释放设备号;
165 return -ENOMEM;
166 }
167
168 static void __exit memdev_exit(void)
169 {
170 int i=0;
171 for(i=0;i < MEMDEV_NR; i++)
172 kfree(memdevp[i].data);//释放数据部分所占用的空间
173 kfree(memdevp);//释放设备结构所占用的空间;
174 unregister_chrdev_region(dev_no,MEMDEV_NR);//注销该设备号;
175 cdev_del(&cdev);//删除设备结构...
176 }
177
178 MODULE_LICENSE("GPL");
179 MODULE_AUTHOR("rzchong");
180
181 module_init(memdev_init);
182 module_exit(memdev_exit);
View Code
