此“设备”是一个在内存中恒久的空间，在模块初始化时便已分配。
使用modinfo查看编译出来的模块信息
$modinfo ./globalmem.ko
将自定义的主设备号作为参数插入到模块中，使用
$sudo insmod ./globalmem.ko globalmem_major=xxx
来分配。
/*======================================================================
A globalmem driver as an example of char device drivers
The initial developer of the original code is Baohua Song
<author@linuxdriver.cn>. All Rights Reserved.
======================================================================*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/slab.h>
#define GLOBALMEM_SIZE 0x1000 /*全局内存最大4K字节*/
#define MEM_CLEAR 0x1 /*清0全局内存*/
#define GLOBALMEM_MAJOR 200 /*预设的globalmem的主设备号*/
static int globalmem_major = GLOBALMEM_MAJOR;
/*globalmem设备结构体*/
struct globalmem_dev
{
struct cdev cdev; /*cdev结构体*/
unsigned char mem[GLOBALMEM_SIZE]; /*全局内存*/
};
struct globalmem_dev *globalmem_devp; /*设备结构体指针*/
/*文件打开函数*/
int globalmem_open(struct inode *inode, struct file *filp)
{
/*将设备结构体指针赋值给文件私有数据指针*/
filp->private_data = globalmem_devp;
return 0;
}
/*文件释放函数*/
int globalmem_release(struct inode *inode, struct file *filp)
{
return 0;
}
/* ioctl设备控制函数 */
static int globalmem_ioctl(struct inode *inodep, struct file *filp, unsigned
int cmd, unsigned long arg)
{
struct globalmem_dev *dev = filp->private_data;/*获得设备结构体指针*/
switch (cmd)
{
case MEM_CLEAR:
memset(dev->mem, 0, GLOBALMEM_SIZE);
printk(KERN_INFO "globalmem is set to zero\n");
break;
default:
return - EINVAL;
}
return 0;
}
/*读函数*/
static ssize_t globalmem_read(struct file *filp, char __user *buf, size_t size,
loff_t *ppos)
{
unsigned long p = *ppos; //这里的p是*ppos的一份拷贝，表示已经读取了的字节数目
unsigned int count = size; //需要读取的字节数
int ret = 0;
struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/
/*分析和获取有效的写长度*/
if (p >= GLOBALMEM_SIZE)
return count ? - ENXIO: 0;
if (count > GLOBALMEM_SIZE - p)//GLOBALMEM_SIZE - p 表示还剩下的可读字节数
count = GLOBALMEM_SIZE - p;
/*内核空间->用户空间*/
if (copy_to_user(buf, (void*)(dev->mem + p), count))
{
ret = - EFAULT;
}
else //假设分配了0x1~0x9共9个字节的空间，读之前p=5表示已读了5个字节，count=5表示需要读6个字节，在函数中count被置9-5=4，因为只能读剩下的4个字节。
{ //读完之后，*ppos = 5 + 4 ，下次再读就返回0了。写和读类似。。。
*ppos += count;
ret = count;
printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
}
return ret;
}
/*写函数*/
static ssize_t globalmem_write(struct file *filp, const char __user *buf,
size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
int ret = 0;
struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/
/*分析和获取有效的写长度*/
if (p >= GLOBALMEM_SIZE)
return count ? - ENXIO: 0;
if (count > GLOBALMEM_SIZE - p)
count = GLOBALMEM_SIZE - p;
/*用户空间->内核空间*/
if (copy_from_user(dev->mem + p, buf, count))
ret = - EFAULT;
else
{
*ppos += count;
ret = count;
printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
}
return ret;
}
/* seek文件定位函数 */
static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig)
{
loff_t ret = 0;
switch (orig)
{
case 0: /*相对文件开始位置偏移*/
if (offset < 0)
{
ret = - EINVAL;
break;
}
if ((unsigned int)offset > GLOBALMEM_SIZE)
{
ret = - EINVAL;
break;
}
filp->f_pos = (unsigned int)offset;
ret = filp->f_pos;
break;
case 1: /*相对文件当前位置偏移*/
if ((filp->f_pos + offset) > GLOBALMEM_SIZE)
{
ret = - EINVAL;
break;
}
if ((filp->f_pos + offset) < 0)
{
ret = - EINVAL;
break;
}
filp->f_pos += offset;
ret = filp->f_pos;
break;
default:
ret = - EINVAL;
break;
}
return ret;
}
/*文件操作结构体*/
static const struct file_operations globalmem_fops =
{
.owner = THIS_MODULE,
.llseek = globalmem_llseek,
.read = globalmem_read,
.write = globalmem_write,
.ioctl = globalmem_ioctl,
.open = globalmem_open,
.release = globalmem_release,
};
/*初始化并注册cdev*/
static void globalmem_setup_cdev(struct globalmem_dev *dev, int index)//index为次设备号
{
int err, devno = MKDEV(globalmem_major, index);//得到总设备号
cdev_init(&dev->cdev, &globalmem_fops);//将字符设备和对设备操作的函数相关联
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &globalmem_fops;
err = cdev_add(&dev->cdev, devno, 1);//将字符设备和内核相关联
if (err)
printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}
/*设备驱动模块加载函数*/
int globalmem_init(void)
{
int result;
dev_t devno = MKDEV(globalmem_major, 0);
/* 申请设备号*/
if (globalmem_major)
result = register_chrdev_region(devno, 1, "globalmem");
else /* 动态申请设备号 */
{
result = alloc_chrdev_region(&devno, 0, 1, "globalmem");
globalmem_major = MAJOR(devno);
}
if (result < 0)
return result;
/* 动态申请设备结构体的内存*/
globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);
if (!globalmem_devp) /*申请失败*/
{
result = - ENOMEM;
goto fail_malloc;
}
memset(globalmem_devp, 0, sizeof(struct globalmem_dev));
globalmem_setup_cdev(globalmem_devp, 0); /*初始化并注册cdev*/
return 0;
fail_malloc: unregister_chrdev_region(devno, 1);
return result;
}
/*模块卸载函数*/
void globalmem_exit(void)
{
cdev_del(&globalmem_devp->cdev); /*注销cdev*/
kfree(globalmem_devp); /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); /*释放设备号*/
}
MODULE_AUTHOR("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");
module_param(globalmem_major, int, S_IRUGO);
module_init(globalmem_init);
module_exit(globalmem_exit);
与设备号相关的宏位于
/usr/src/linux-headers-2.6.35-22/include/linux/kdev_t.h
总设备号，主设备号，次设备号 1 #ifndef _LINUX_KDEV_T_H 2 #define _LINUX_KDEV_T_H 3 #ifdef __KERNEL__ //若已定义__KERNEL__符号则MAJOR 4 #define MINORBITS 20 5 #define MINORMASK ((1U << MINORBITS) - 1) 6 7 #define MAJOR(dev) ((unsigned int) ((dev) >> MINORBITS))//左移20位得到高12为作为主设备号 8 #define MINOR(dev) ((unsigned int) ((dev) & MINORMASK))//MINORMASK为20个1（二进制），取低20位作为次设备号 9 #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi)) //将ma放在高12位，mi放在低20位 90 #else /* __KERNEL__ *///未定义__KERNEL__符号 91 92 /* 93 Some programs want their definitions of MAJOR and MINOR and MKDEV 94 from the kernel sources. These must be the externally visible ones. 95 */ 96 #define MAJOR(dev) ((dev)>>8) //这里就是左移8位 97 #define MINOR(dev) ((dev) & 0xff) //取低8位作为次设备号 98 #define MKDEV(ma,mi) ((ma)<<8 | (mi)) //ma左移8位并上mi 99 #endif /* __KERNEL__ */ 100 #endif
Makefile如下，稍微加了一点改进
OBJ = globalmem
obj-m += $(OBJ).o
MAJOR = 200
MINOR = 0
#generate the path
CURRENT_PATH:=$(shell pwd)
#the current kernel version number
LINUX_KERNEL:=$(shell uname -r)
#the absolute path
LINUX_KERNEL_PATH:=/usr/src/linux-headers-$(LINUX_KERNEL)
#complie object
all:
make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules
install:
sudo insmod ./$(OBJ).ko
sudo mknod /dev/my_$(OBJ) c $(MAJOR) $(MINOR)
uninstall:
sudo rmmod $(OBJ)
sudo rm -rf /dev/my_$(OBJ)
#clean
clean:
make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean
可以使用命令来测试设备
#ls > /dev/my_globalmem
#cat /dev/my_globalmem
或者用测试程序
这里的程序是从设备中读取数据，测试之前要先向设备中写入数据。
#cat file > /dev/my_globalmem
/*main.c*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
int main(void)
{
int testdev;
int i,rf=0;
char buf[100];
memset(buf, 0, sizeof(buf));
testdev = open("/dev/my_globalmem",O_RDWR); //open the device
if ( testdev == -1 )
{
perror("open\n");
exit(0);
}
for(i=0;i<10;i++)
{
rf=read(testdev,buf,100); //read some bytes from the device and put the data to buf
if(rf<0)
perror("read error\n");
printf("times %d ,Read:\n%s", i, buf);
printf("\ntimes %d ,Read finish\n", i);
}
close(testdev); //close the device
return 0;
这是有两个globalmem“设备”的驱动程序，只需要更改设备初始化函数和卸载函数
/*设备驱动模块加载函数*/
int globalmem_init(void)
{
int result;
dev_t devno = MKDEV(globalmem_major, 0);
/* 申请设备号*/
if (globalmem_major)
result = register_chrdev_region(devno, 2, "globalmem");//申请使用两个总设备号
else /* 动态申请设备号 */
{
result = alloc_chrdev_region(&devno, 0, 2, "globalmem");
globalmem_major = MAJOR(devno);
}
if (result < 0)
return result;
/* 动态申请2个设备结构体的内存*/
globalmem_devp = kmalloc(2*sizeof(struct globalmem_dev), GFP_KERNEL);
if (!globalmem_devp) /*申请失败*/
{
result = - ENOMEM;
goto fail_malloc;
}
memset(globalmem_devp, 0, 2*sizeof(struct globalmem_dev));
globalmem_setup_cdev(&globalmem_devp[0], 0);//从设备号为0
globalmem_setup_cdev(&globalmem_devp[1], 1);//从设备号为1
return 0;
fail_malloc: unregister_chrdev_region(devno, 2);
return result;
}
/*模块卸载函数*/
void globalmem_exit(void)
{
cdev_del(&(globalmem_devp[0].cdev));
cdev_del(&(globalmem_devp[1].cdev)); /*注销cdev*/
kfree(globalmem_devp); /*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(globalmem_major, 0), 2); /*释放设备号*/
}
我们可以看到以上程序是没有加锁的，在对设备的read，write，ioctl操作中会产生竞态，多个进程同时访问的话，驱动极易崩溃。
所以在对这块内存“设备”做操作时（读，写，清空），要加锁。
注意/dev下建立的设备文件和驱动程序中设置的主从设备号一定要一致，不然是无法读取的。