字符设备驱动开发

本驱动笔记，都是记录宋宝华的驱动书籍，代码也是参考他的，撰写文章，主要记录学习心得

1.字符驱动，作者用globalmem这样的例子来讲解驱动。
问题1.insmod globalmem.ko驱动。如何和mknod 创建的设备绑定的。
答：通过主设备号来绑定。
问题2.insmod globalmem.ko,会失败，提示Device or resource busy
答：这是主设备号冲突导致的，默认sample里面是固定主设备号，需要修改为动态分配设备号。
问题3：动态分配主设备号，如何知道分配主设备是多少
答：cat /proc/devices 可以看到主设备号的分配

附录，单一设备的驱动代码和makefile

`#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 <linux/uaccess.h>

include<linux/slab.h>

define GLOBAMEM_SIZE 0x1000

define MEM_CLEAR 0X1

define GLOBALMEM_MAJOR 0

static int globalmem_major = GLOBALMEM_MAJOR;
/* globalmem设备结构体 */
struct globalmem_dev {
struct cdev cdev;
unsigned char mem[GLOBAMEM_SIZE];
};

struct globalmem_dev globalmem_devp;
/ 文件打开函数 */
int globalmem_open(struct inode *inode, struct file filp)
{
/ /
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 long globalmem_ioctl(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, GLOBAMEM_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;
unsigned int count = size;
int ret = 0;
struct globalmem_dev *dev = filp->private_data;/* 获得设备结构体指针 */ 


if (p >= GLOBAMEM_SIZE)
	return 0;
if (count > GLOBAMEM_SIZE - p)
	count = GLOBAMEM_SIZE - p;

/* 内核空间--> 用户空间 */
if (copy_to_user(buf, (void *)(dev->mem + p), count)) {
	ret = EFAULT;
}else {
	*ppos += count;
	ret = count;

	printk(KERN_INFO "read %u bytes(s) from %lu\n", count, p);
}

return ret;

}
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 */ 


if (p >= GLOBAMEM_SIZE)
	return 0;
if (count > GLOBAMEM_SIZE - p)
	count = GLOBAMEM_SIZE - p;

/* 用户空间--> 内核空间 */
if (copy_from_user((void *)(dev->mem + p), buf,count)) {
	ret = EFAULT;
}else {
	*ppos += count;
	ret = count;

	printk(KERN_INFO "write %u bytes(s) from %lu\n", count, p);
}

return ret;

}
static loff_t globalmem_llseek(struct file *filp, loff_t offset,int orig)
{

int ret = 0;
struct globalmem_dev *dev = filp->private_data;/* 获得设备结构体指针 */ 



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,
.unlocked_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)
{
int err, devno = MKDEV(globalmem_major, index);

cdev_init(&dev->cdev, &globalmem_fops);
dev->cdev.owner = THIS_MODULE;
err = cdev_add(&dev->cdev, devno, 1);
if (err)
	printk(KERN_NOTICE "Error %d adding globalmem %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); / devno = (250<<20) | 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);
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("Fourier");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);

makefile如下：KVERS = $(shell uname -r)
obj-m += dev.o
build: kernel_modules
kernel_modules:
make -C /lib/modules/$(KVERS)/build M=$(CURDIR) modules
clean:
make -C /lib/modules/$(KVERS)/build M=$(CURDIR) clean`