Linux杂项设备

Linux杂项设备驱动简介

什么是杂项设备

杂项设备是字符设备的一种。可以自动生成设备节点。Linux系统里有很多的杂项设备。我们可以输入 cat /proc/misc命令来查看

杂项设备和普通字符设备的区别

  1. 杂项设备比字符设备代码简单
  2. 杂项设备的主设备号是相同的，均为10,次设备号是不同的。主设备号相同就可以节省内核资源。

主设备号和次设备号是什么

  1. 设备号包含主设备号和次设备号，主设备号在Linux系统里面是唯一的，次设备号不一定唯一。
  2. 设备号是计算机识别设备的一种方式，主设备相同的就被试为同一类设备
  3. 主设备号可以通过命令 cat /proc/devices来查看

杂项设备的描述

杂项设备的结构体在源码 include/linux/miscdevice.h。vim include/linux/miscdevice.h 查看

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struct miscdevice  {
        int minor; //次设备号
        const char *name; //设备节点的名字
        const struct file_operations *fops; //文件操作集
		// 下面的一般不用
        struct list_head list;
        struct device *parent;
        struct device *this_device;
        const struct attribute_group **groups;
        const char *nodename;
        umode_t mode;
};

file_operations结构体在linux源码中 include/linux/fs.h ,该结构体里的每一个结构体成员都对应一个调用。

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struct file_operations {
        struct module *owner;
        loff_t (*llseek) (struct file *, loff_t, int);
        ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
        ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
        ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
        ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
        int (*iterate) (struct file *, struct dir_context *);
        unsigned int (*poll) (struct file *, struct poll_table_struct *);
        long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
        long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
        int (*mmap) (struct file *, struct vm_area_struct *);
        int (*mremap)(struct file *, struct vm_area_struct *);
        int (*open) (struct inode *, struct file *);
        int (*flush) (struct file *, fl_owner_t id);
        int (*release) (struct inode *, struct file *);
        int (*fsync) (struct file *, loff_t, loff_t, int datasync);
        int (*aio_fsync) (struct kiocb *, int datasync);
        int (*fasync) (int, struct file *, int);
        int (*lock) (struct file *, int, struct file_lock *);
        ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
        unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
        int (*check_flags)(int);
        int (*flock) (struct file *, int, struct file_lock *);
        ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
        ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
        int (*setlease)(struct file *, long, struct file_lock **, void **);
        long (*fallocate)(struct file *file, int mode, loff_t offset,
                          loff_t len);
        void (*show_fdinfo)(struct seq_file *m, struct file *f);
#ifndef CONFIG_MMU
        unsigned (*mmap_capabilities)(struct file *);
#endif
};

杂项设备的注册和注销

在源码 include/linux/miscdevice.h 中有函数声明

注册杂项设备

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extern int misc_register(struct miscdevice *misc);

注销杂项设备

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extern int misc_deregister(struct miscdevice *misc);

注册杂项设备的流程

  1. 填充miscdevice这个结构体
  2. 填充file_operation这个结构体
  3. 注册杂项设备，并生成设备节点

杂项设备编写例程

目标

按照杂项设备的注册流程注册一个杂项设备，并生成设备节点。

例程代码

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#include <linux/init.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>

struct file_operations misc_fops = {
	.owner = THIS_MODULE
};

struct miscdevice misc_dev ={
	.minor = MISC_DYNAMIC_MINOR, //自动分配次设备号
	.name  = "hello_misc",
	.fops  = &misc_fops
};

static int misc_init(void)
{
	int ret;
	ret = misc_register(&misc_dev);
	if(ret < 0)
	{
		printk("misc register is error\n");
		return -1;
	}
	printk("misc is succeed\n");
	return 0;
}

static void misc_exit(void)
{
	misc_deregister(&misc_dev);
	printk("misc by by\n");
}

module_init(misc_init);
module_exit(misc_exit);
MODULE_LICENSE("GPL");