驱动14.字符设备的另一种写法

Posted 2020-08-29 wade_linux

原本的字符设备只能有255个驱动程序，原因是一个主设备号占用了0~255的次设备号

把register_chrdev展开可得到一下几个部分：register_chrdev_region/alloc_chrdev_region,cdev_init,cdev_add

参照register_chrdev的写法完成hello.c的代码

 1 #include <linux/module.h>
 2 #include <linux/kernel.h>
 3 #include <linux/fs.h>
 4 #include <linux/init.h>
 5 #include <linux/delay.h>
 6 #include <linux/irq.h>
 7 #include <asm/uaccess.h>
 8 #include <asm/irq.h>
 9 #include <asm/io.h>
10 #include <asm/arch/regs-gpio.h>
11 #include <asm/hardware.h>
12 #include <linux/poll.h>
13 #include <linux/cdev.h>
14 
15 static int major;
16 
17 static int hello_open(struct inode *inode, struct file *file)
18 {
19     printk("hello_open\\n");
20     return 0;
21 }
22 
23 static int hello2_open(struct inode *inode, struct file *file)
24 {
25     printk("hello2_open\\n");
26     return 0;
27 }
28 
29 
30 
31 static struct file_operations hello_fops = {
32     .owner = THIS_MODULE,
33     .open  = hello_open,
34 };
35 
36 static struct file_operations hello2_fops = {
37     .owner = THIS_MODULE,
38     .open  = hello2_open,
39 };
40 
41 #define HELLO_CNT   2
42 
43 static struct cdev hello_cdev;
44 static struct cdev hello2_cdev;
45 static struct class *cls;
46 
47 
48 static int hello_init(void)
49 {
50     dev_t devid;
51 
52     if (major) {
53         devid = MKDEV(major, 0);
54         register_chrdev_region(devid, HELLO_CNT, "hello");
55     } else {
56         alloc_chrdev_region(&devid, 0, HELLO_CNT, "hello");
57         major = MAJOR(devid);
58     }
59     cdev_init(&hello_cdev, &hello_fops);
60     cdev_add(&hello_cdev, devid, HELLO_CNT);
61 
62     devid = MKDEV(major, 2);
63     register_chrdev_region(devid, 1, "hello2");
64     cdev_init(&hello2_cdev, &hello2_fops);
65     cdev_add(&hello2_cdev, devid, 1);
66 
67     cls = class_create(THIS_MODULE, "hello");
68     class_device_create(cls, NULL, MKDEV(major, 0), NULL, "hello0"); /* /dev/hello0 */
69     class_device_create(cls, NULL, MKDEV(major, 1), NULL, "hello1"); /* /dev/hello1 */
70     class_device_create(cls, NULL, MKDEV(major, 2), NULL, "hello2"); /* /dev/hello2 */
71     class_device_create(cls, NULL, MKDEV(major, 3), NULL, "hello3"); /* /dev/hello3 */
72     
73     
74     return 0;
75     
76 }
77 
78 static void hello_exit(void)
79 {
80     class_device_destroy(cls, MKDEV(major, 0));
81     class_device_destroy(cls, MKDEV(major, 1));
82     class_device_destroy(cls, MKDEV(major, 2));
83     class_device_destroy(cls, MKDEV(major, 3));
84     class_destroy(cls);
85 
86     cdev_del(&hello_cdev);
87     unregister_chrdev_region(MKDEV(major, 0), HELLO_CNT);
88 
89     cdev_del(&hello2_cdev);
90     unregister_chrdev_region(MKDEV(major, 2), 1);
91 }
92 
93 module_init(hello_init);
94 module_exit(hello_exit);
95 
96 
97 MODULE_LICENSE("GPL");

hello.c

 

(major,0~1)对应于hello，即/dev/hello0,/dev/hello1

(major,2)对应于hello2,即/dev/hello2

/dev/hello3打不开