目录
title: 指定子设备号创建字符设备
tags: linux date: 2018/12/28 19:57:24 toc: true ---指定子设备号字符设备
流程
内核中设备号分为主设备号和次设备号,以前注册字符设备驱动的时候,直接占用了主设备号包含了255个子设备号,也就是内核最多支持255个设备驱动(如果主设备号占据8位)
在Linux2.6中内核可以指定主设备号和对应的子设备号给一个fileoperation,如下图所示
流程如下:
确认需要得到几个子设备号使用
如果指定主设备号使用
register_chrdev_region,当返回值小于0,表示注册失败dev_t devid;devid = MKDEV(major, 0);/* (major,0~1) 对应 hello_fops, (major, 2~255)都不对应hello_fops */register_chrdev_region(devid, HELLO_CNT, "hello");
如果需要系统分配主设备号,
alloc_chrdev_region(&devid, 0, HELLO_CNT, "hello");当返回值小于0,表示注册失败/* (major,0~1) 对应 hello_fops, (major, 2~255)都不对应hello_fops */alloc_chrdev_region(&devid, 0, HELLO_CNT, "hello");major = MAJOR(devid);
这里使用
cdev管理驱动,并将file_operations结构体放入cdev-> ops里cdev_init(&hello_cdev, &hello_fops);cdev_add(&hello_cdev, devid, HELLO_CNT);struct cdev { struct kobject kobj; // 内嵌的kobject对象 struct module *owner; //所属模块 const struct file_operations *ops; //操作方法结构体 struct list_head list; //与 cdev 对应的字符设备文件inode->i_devices 的链表头 dev_t dev; //起始设备编号,可以通过MAJOR(),MINOR()来提取主次设备号 unsigned int count; //连续注册的次设备号个数};创建设备文件是与以前一样的,使用
class_create创建类和class_device_create创建设备文件卸载
/*将系统中的cdev结构体删除掉*/void cdev_del(struct cdev *p); /*注销字符设备*/void unregister_chrdev_region(dev_t from, unsigned count);
实例程序
#include#include #include #include #include #include #include #include #include #include #include #include #include /* 1. 确定主设备号 */static int major;static int hello_open(struct inode *inode, struct file *file){ printk("hello_open\n"); return 0;}static int hello2_open(struct inode *inode, struct file *file){ printk("hello2_open\n"); return 0;}/* 2. 构造file_operations */static struct file_operations hello_fops = { .owner = THIS_MODULE, .open = hello_open,};static struct file_operations hello2_fops = { .owner = THIS_MODULE, .open = hello2_open,};#define HELLO_CNT 2static struct cdev hello_cdev;static struct cdev hello2_cdev;static struct class *cls;static int hello_init(void){ dev_t devid; /* 3. 告诉内核 */#if 0 major = register_chrdev(0, "hello", &hello_fops); /* (major, 0), (major, 1), ..., (major, 255)都对应hello_fops */#else if (major) { devid = MKDEV(major, 0); register_chrdev_region(devid, HELLO_CNT, "hello"); /* (major,0~1) 对应 hello_fops, (major, 2~255)都不对应hello_fops */ } else { alloc_chrdev_region(&devid, 0, HELLO_CNT, "hello"); /* (major,0~1) 对应 hello_fops, (major, 2~255)都不对应hello_fops */ major = MAJOR(devid); } cdev_init(&hello_cdev, &hello_fops); cdev_add(&hello_cdev, devid, HELLO_CNT); devid = MKDEV(major, 2); register_chrdev_region(devid, 1, "hello2"); cdev_init(&hello2_cdev, &hello2_fops); cdev_add(&hello2_cdev, devid, 1); #endif cls = class_create(THIS_MODULE, "hello"); class_device_create(cls, NULL, MKDEV(major, 0), NULL, "hello0"); /* /dev/hello0 */ class_device_create(cls, NULL, MKDEV(major, 1), NULL, "hello1"); /* /dev/hello1 */ class_device_create(cls, NULL, MKDEV(major, 2), NULL, "hello2"); /* /dev/hello2 */ class_device_create(cls, NULL, MKDEV(major, 3), NULL, "hello3"); /* /dev/hello3 */ return 0;}static void hello_exit(void){ class_device_destroy(cls, MKDEV(major, 0)); class_device_destroy(cls, MKDEV(major, 1)); class_device_destroy(cls, MKDEV(major, 2)); class_device_destroy(cls, MKDEV(major, 3)); class_destroy(cls); cdev_del(&hello_cdev); unregister_chrdev_region(MKDEV(major, 0), HELLO_CNT); cdev_del(&hello2_cdev); unregister_chrdev_region(MKDEV(major, 2), 1);}module_init(hello_init);module_exit(hello_exit);MODULE_LICENSE("GPL");
测试
查看到只是用了同一个主设备号
cat /proc/devices# cat /proc/devicesCharacter devices:252 hello #同一个主设备号252 hello2 #同一个主设备号
查看设备文件
# ls /dev/hello* -lcrw-rw---- 1 0 0 252, 0 Jan 1 04:18 /dev/hello0crw-rw---- 1 0 0 252, 1 Jan 1 04:18 /dev/hello1crw-rw---- 1 0 0 252, 2 Jan 1 04:18 /dev/hello2crw-rw---- 1 0 0 252, 3 Jan 1 04:18 /dev/hello3
| 驱动fileopration | 次设备号 |
|---|---|
| hello_fops | 0,1 |
| hello2_fops | 2 |
也就是对应设备文件的驱动如下
| 设备文件 | |
|---|---|
| /dev/hello0 | hello_fops |
| /dev/hello1 | hello_fops |
| /dev/hello2 | hello2_fops |
| /dev/hello3 | 没有 |
使用测试文件去打开文件如下结果
# ./test /dev/hello0hello_open #驱动1打开的can open /dev/hello0# ./test /dev/hello1hello_open #驱动1打开的can open /dev/hello1# ./test /dev/hello2hello2_open #驱动2打开的can open /dev/hello2# ./test /dev/hello3can't open /dev/hello3 #无法打开
测试程序如下
//arm-linux-gcc -o test test.c#include#include #include #include #include #include /* * test /dev/hello0 */void print_usage(char *file){ printf("%s \n", file);}int main(int argc, char **argv){ int fd; if (argc != 2) { print_usage(argv[0]); return 0; } fd = open(argv[1], O_RDWR); if (fd < 0) printf("can't open %s\n", argv[1]); else printf("can open %s\n", argv[1]); return 0;}