8.【linux驱动】ioctl

函数原型

long (*unlocked_ioctl) (struct file *fl, unsigned int cmd, unsigned long arg);

ioctl的cmd参数可以自定义使用规则，但是内核也有一个规范

 1). 最高两位表示方向： 读/写/读写(输出/输入/输出输入)
 2). 第16位至第29位表示ioctl的第三个参数的大小(unlocked_ioctl的arg).
 3). 第8位至第15位表示ioctl命令的类型.
 4). 最低8位表示ioctl命令类型里的第几个命令

内核宏定义

有关cmd位的操作方式在内核中已经定义好了相关的宏给我们使用，另外在应用层也有同样的一份可以使用
include/asm-generic/ioctl.h:

#ifndef _ASM_GENERIC_IOCTL_H
#define _ASM_GENERIC_IOCTL_H

/* ioctl command encoding: 32 bits total, command in lower 16 bits,
 * size of the parameter structure in the lower 14 bits of the
 * upper 16 bits.
 * Encoding the size of the parameter structure in the ioctl request
 * is useful for catching programs compiled with old versions
 * and to avoid overwriting user space outside the user buffer area.
 * The highest 2 bits are reserved for indicating the ``access mode''.
 * NOTE: This limits the max parameter size to 16kB -1 !
 */

/*
 * The following is for compatibility across the various Linux
 * platforms.  The generic ioctl numbering scheme doesn't really enforce
 * a type field.  De facto, however, the top 8 bits of the lower 16
 * bits are indeed used as a type field, so we might just as well make
 * this explicit here.  Please be sure to use the decoding macros
 * below from now on.
 */
#define _IOC_NRBITS	8
#define _IOC_TYPEBITS	8

/*
 * Let any architecture override either of the following before
 * including this file.
 */

#ifndef _IOC_SIZEBITS
# define _IOC_SIZEBITS	14
#endif

#ifndef _IOC_DIRBITS
# define _IOC_DIRBITS	2
#endif

#define _IOC_NRMASK	((1 << _IOC_NRBITS)-1)
#define _IOC_TYPEMASK	((1 << _IOC_TYPEBITS)-1)
#define _IOC_SIZEMASK	((1 << _IOC_SIZEBITS)-1)
#define _IOC_DIRMASK	((1 << _IOC_DIRBITS)-1)

#define _IOC_NRSHIFT	0
#define _IOC_TYPESHIFT	(_IOC_NRSHIFT+_IOC_NRBITS)
#define _IOC_SIZESHIFT	(_IOC_TYPESHIFT+_IOC_TYPEBITS)
#define _IOC_DIRSHIFT	(_IOC_SIZESHIFT+_IOC_SIZEBITS)

/*
 * Direction bits, which any architecture can choose to override
 * before including this file.
 */

#ifndef _IOC_NONE
# define _IOC_NONE	0U
#endif

#ifndef _IOC_WRITE
# define _IOC_WRITE	1U
#endif

#ifndef _IOC_READ
# define _IOC_READ	2U
#endif

#define _IOC(dir,type,nr,size) \
	(((dir)  << _IOC_DIRSHIFT) | \
	 ((type) << _IOC_TYPESHIFT) | \
	 ((nr)   << _IOC_NRSHIFT) | \
	 ((size) << _IOC_SIZESHIFT))

#ifdef __KERNEL__
/* provoke compile error for invalid uses of size argument */
extern unsigned int __invalid_size_argument_for_IOC;
#define _IOC_TYPECHECK(t) \
	((sizeof(t) == sizeof(t[1]) && \
	  sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
	  sizeof(t) : __invalid_size_argument_for_IOC)
#else
#define _IOC_TYPECHECK(t) (sizeof(t))
#endif

/* used to create numbers */
#define _IO(type,nr)		_IOC(_IOC_NONE,(type),(nr),0)
#define _IOR(type,nr,size)	_IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOW(type,nr,size)	_IOC(_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOWR(type,nr,size)	_IOC(_IOC_READ|_IOC_WRITE,(type),(nr),(_IOC_TYPECHECK(size)))
#define _IOR_BAD(type,nr,size)	_IOC(_IOC_READ,(type),(nr),sizeof(size))
#define _IOW_BAD(type,nr,size)	_IOC(_IOC_WRITE,(type),(nr),sizeof(size))
#define _IOWR_BAD(type,nr,size)	_IOC(_IOC_READ|_IOC_WRITE,(type),(nr),sizeof(size))

/* used to decode ioctl numbers.. */
#define _IOC_DIR(nr)		(((nr) >> _IOC_DIRSHIFT) & _IOC_DIRMASK)
#define _IOC_TYPE(nr)		(((nr) >> _IOC_TYPESHIFT) & _IOC_TYPEMASK)
#define _IOC_NR(nr)		(((nr) >> _IOC_NRSHIFT) & _IOC_NRMASK)
#define _IOC_SIZE(nr)		(((nr) >> _IOC_SIZESHIFT) & _IOC_SIZEMASK)

/* ...and for the drivers/sound files... */

#define IOC_IN		(_IOC_WRITE << _IOC_DIRSHIFT)
#define IOC_OUT		(_IOC_READ << _IOC_DIRSHIFT)
#define IOC_INOUT	((_IOC_WRITE|_IOC_READ) << _IOC_DIRSHIFT)
#define IOCSIZE_MASK	(_IOC_SIZEMASK << _IOC_SIZESHIFT)
#define IOCSIZE_SHIFT	(_IOC_SIZESHIFT)

#endif /* _ASM_GENERIC_IOCTL_H */

应用

简单打印一下参数，向用户空间写入值

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <asm/uaccess.h>

MODULE_LICENSE("GPL");

static int data = 1;
module_param(data, int, 0644);  //声明模块参数
dev_t devid;
struct cdev char_dev;
struct class * char_class;
int buffer_size = 100;
char * char_data;

static int open(struct inode * node, struct file * fl){
	return 0;
}

static long ioctl(struct file * fl, unsigned int cmd, unsigned long arg){
	printk("dir:%d,size:%d,type:%d,nr:%d\n",_IOC_DIR(cmd),_IOC_SIZE(cmd),_IOC_TYPE(cmd),_IOC_NR(cmd));
	printk("arg:%ld\n",arg);
	*(int *)arg = 123;
	return 0;
}

static ssize_t read(struct file * fl, char __user * buf, size_t len, loff_t * offset){
	return 0;
}

static ssize_t write(struct file * fl, const char __user * buf, size_t len, loff_t * offset){
	return 0;
}

struct file_operations my_opts = {
	.owner = THIS_MODULE,
	.open = open,
	.read = read,
	.write = write,
	.unlocked_ioctl = ioctl
};

static int __init char_init(void){
	int ret = 0;

    devid = MKDEV(241, 1);								//换算设备号
    ret = register_chrdev_region(devid, 1, "char_test");//注册设备，在/proc/drivers下面可以看到
    if (ret < 0)
        goto err0;

    cdev_init(&char_dev,&my_opts);						//绑定opt结构体
    char_dev.owner = THIS_MODULE;
    ret = cdev_add(&char_dev,devid,1);					//注册字符设备驱动
    if (ret < 0)
    	goto err1;

    char_class = class_create(THIS_MODULE,"char_test"); //在/sys/class中创建文件夹
    device_create(char_class,NULL,devid,NULL,"char_test_dev_%d",1);//在上一步文件夹中创建char_test_dev_1

    char_data = kzalloc(buffer_size,GFP_KERNEL);

	printk("char init\n");
    return 0;

	err1:
	    unregister_chrdev_region(devid, 1);
    err0:
        return ret;
}

static void __exit char_exit(void){
	unregister_chrdev_region(devid, 1);
	cdev_del(&char_dev);
	device_destroy(char_class,devid);
	class_destroy(char_class);
	printk("char exit\n");
}

module_init(char_init);
module_exit(char_exit);

应用层代码

#include <stdio.h>
#include <linux/ioctl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>

int main(){
	int ret,cmd,arg;
	ret = open("/dev/char_test_dev_1",O_RDWR);
	if(ret < 0){
		perror("open /dev/char_test_dev_1 error");
		return ret;
	}
	cmd = _IOC(_IOC_READ,0x01,0x02,0x03);
	ret = ioctl(ret,cmd,&arg);
	if(ret < 0){
		perror("ioctl error");
		return ret;
	}
	printf("arg:%d\n", arg);
	close(ret);
	return 0;
}

贴一下Makefile

KERNEL_DIR := 内核目录
CC := arm-linux-gcc

all:hello main
.PHONY:all

hello:
	make -C ${KERNEL_DIR} M=`pwd` modules

main:
	${CC} main.c -o main


.PHONY:
clean:
	make -C ${KERNEL_DIR} M=`pwd` clean

obj-m += ioctl.o

运行结果

[root@minicoco ioctl]# insmod ioctl.ko
[136878.712000] char init
[root@minicoco ioctl]# ./main
[136881.760000] dir:2,size:3,type:1,nr:2
[136881.764000] arg:-1096856324
arg:123
[root@minicoco ioctl]#