平臺：VMware 7.0 + Linux ubuntu 3.0.0-12-generic
編譯器：gcc
參考資料：LDD 3
功能：實現ioctl功能
在Linux字符設備驅動入門（一）中，我們實現了字符設備的簡單讀寫字符功能，接下來我們要在這個基礎上加入ioctl功能。首先，我們先來看看3.0內核下../include/linux/fs.h中file_operations結構體的定義：
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);
};
紅色字體已經標出在kernel 3.0中已經完全刪除了struct file_operations 中的ioctl 函數指針，剩下unlocked_ioctl和compat_ioctl，取而代之的是unlocked_ioctl,主要改進就是不再需要上大內核鎖 （調用之前不再先調用lock_kernel()然後再unlock_kernel()）。
所以，在hellow.c中，我們在file_operations中加入成員函數hello_ioctl(紅色字體部分）：
/* 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()的定義如下：
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;
}
這裏強調一下cmd的定義：
#define HELLO_MAGIC 'k'
#define HELLO_CMD1 _IO(HELLO_MAGIC,0x1a)
#define HELLO_CMD2 _IO(HELLO_MAGIC,0x1b)
其中'k'爲幻數，要按照Linux內核的約定方法爲驅動程序選擇ioctl編號，應該首先看看include/asm/ioctl.h和Documentation/ioctl-number.txt這兩個文件，下面是ioctl.h的部分內容，也是比較重要的：
_IO(type, nr)
用於構造無參數的命令編號；
_IOR(type, nr, datatype)
用於構造從驅動程序中讀取數據的命令編號；
_IOW(type, nr, datatype)
用於寫入數據的命令；
_IOWR(type, nr, datatype)
用於雙向傳輸。注意千萬不能重複定義。
注意對幻數的編號千萬不能重複定義，如ioctl-number.txt已經說明‘k'的編號已經被佔用的範圍爲：
'k' 00-0F linux/spi/spidev.h conflict!
'k' 00-05 video/kyro.h conflict!
所以我們在這裏分別編號爲0x1a和0x1b，到這裏，我們已經完成了對ioctl功能的編寫，接下來就是在測試程序中利用系統調用來測試它。
=============================================================
ioctl測試程序
=============================================================
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/ioctl.h>
#define HELLO_MAGIC 'k' //當然我們也可以定義一個相應的頭文件，把ioctl的cmd放進裏面，然後再include進 來
#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;
}
=============================================================
運行結果
=============================================================
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!