在Linux字符设备驱动入门(一)中，我们实现了字符设备的简单读写字符功能，接下来我们要在这个基础上加入ioctl功能。首先，我们先来看看3.0内核下../include/linux/fs.h中file_operations结构体的定义：
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 (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
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 (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, 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 **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
};
红色字体已经标出在kernel 3.0中已经完全删除了struct file_operations 中的ioctl 函数指针，剩下unlocked_ioctl和compat_ioctl，取而代之的是unlocked_ioctl,主要改进就是不再需要上大内核锁 (调用之前不再先调用lock_kernel()然后再unlock_kernel())。
所以，在hellow.c中，我们在file_operations中加入成员函数hello_ioctl(红色字体部分)：
/* file operations for hello device */
static struct file_operations hello_ops = {
.owner = THIS_MODULE,
.unlocked_ioctl = hello_ioctl,
.open = hello_open,
.read = hello_read,
.write = hello_write,
.release = hello_release,
};
hello_ioctl()的定义如下：
static int hello_ioctl( struct file *file,
unsigned int cmd, unsigned long arg)
{ int temp = 0;
switch(cmd)
{
case HELLO_CMD1:
{
temp = 1;
if(copy_to_user( (int *)arg, &temp, sizeof(int))) return -EFAULT;
break;
}
case HELLO_CMD2:
{
temp = 2;
if(copy_to_user( (int *)arg, &temp, sizeof(int))) return -EFAULT;
break;
}
}
printk( KERN_NOTICE"ioctl CMD%d done!\n",temp);
return 0;
}
这里强调一下cmd的定义：
#define HELLO_MAGIC 'k'
#define HELLO_CMD1 _IO(HELLO_MAGIC,0x1a)
#define HELLO_CMD2 _IO(HELLO_MAGIC,0x1b)
其中'k'为幻数，要按照Linux内核的约定方法为驱动程序选择ioctl编号，应该首先看看include/asm/ioctl.h和Documentation/ioctl-number.txt这两个文件，下面是ioctl.h的部分内容，也是比较重要的：
_IO(type, nr)
用于构造无参数的命令编号；
_IOR(type, nr, datatype)
用于构造从驱动程序中读取数据的命令编号；
_IOW(type, nr, datatype)
用于写入数据的命令；
_IOWR(type, nr, datatype)
用于双向传输。注意千万不能重复定义。
注意对幻数的编号千万不能重复定义，如ioctl-number.txt已经说明‘k'的编号已经被占用的范围为：
'k' 00-0F linux/spi/spidev.h conflict!
'k' 00-05 video/kyro.h conflict!
所以我们在这里分别编号为0x1a和0x1b，到这里，我们已经完成了对ioctl功能的编写，接下来就是在测试程序中利用系统调用来测试它。
=============================================================
ioctl测试程序
=============================================================
#include
#include
#include
#include
#include
#include
#include
#include
#define HELLO_MAGIC 'k' //当然我们也可以定义一个相应的头文件，把ioctl的cmd放进里面，然后再include进 来
#define HELLO_CMD1 _IO(HELLO_MAGIC,0x1a)
#define HELLO_CMD2 _IO(HELLO_MAGIC,0x1b)
int main(void)
{
int ioctl_rdata;
int fd, ret;
fd = open ( "/dev/hellow" , O_RDWR);
if ( fd == -1 )
{
perror("open");
exit(0);
}
ret = ioctl( fd, HELLO_CMD2,&ioctl_rdata);
if ( ret == -1)
{
perror("ioctl");
exit(0);
}
printf("ioctl_rdata= %d \n",ioctl_rdata);
close(fd);
return 0;
}
=============================================================
运行结果
=============================================================
root@Ubuntu:~/share/hellow# insmod hellow.ko
root@Ubuntu:~/share/hellow# mknod /dev/hellow c 251 0
root@Ubuntu:~/share/hellow# ./a.out
ioctl_rdata= 2
root@Ubuntu:~/share/hellow# dmesg | tail
[ 2431.126532] hello init. major:251, minor:0
[ 2453.326022] Hello device open!
[ 2453.326047] ioctl CMD2 done! [ 2453.326487] Hello device close!
