前面一篇文章，自己记录了字符设备开发。实现内存数据的读写，但是有个问题，设备的创建，需要依靠手动的mknod来创建，有没有改进，直接加载驱动，
就可以完成设备的自动创建了，这里增加了class_create的创建，实现驱动的加载和设备创建，同步触发。对应平台性的设备来说，这样的创建，也是可以接受的。
代码附录如下：

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

define INSMOD_CREATE_DEV

static int globalmem_major = GLOBALMEM_MAJOR;
static struct class *gmem_class;/* 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)
{

ifdef INSMOD_CREATE_DEV

globalmem_major = register_chrdev(0, "gmem", &globalmem_fops);gmem_class = class_create(THIS_MODULE,"gmem");device_create(gmem_class, NULL, MKDEV(globalmem_major, 0), NULL, "mgem"); /* /dev/led */globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);if (!globalmem_devp) { /* 申请失败 */printk(KERN_NOTICE "Error kmalloc failed");}return 0;

else

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;

endif

}/* 模块卸载函数 */
void globalmem_exit(void)
{

ifdef INSMOD_CREATE_DEV

unregister_chrdev(globalmem_major, "gmem");device_destroy(gmem_class,  MKDEV(globalmem_major, 0));class_destroy(gmem_class);

else

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 */

endif

}

MODULE_AUTHOR("Fourier");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);