字元裝置驅動開發
本驅動筆記，都是記錄宋寶華的驅動書籍，程式碼也是參考他的，撰寫文章，主要記錄學習心得
1.字元驅動，作者用globalmem這樣的例子來講解驅動。
問題1.insmod globalmem.ko驅動。如何和mknod 建立的裝置繫結的。
答：通過主裝置號來繫結。
問題2.insmod globalmem.ko,會失敗，提示Device or resource busy
答：這是主裝置號衝突導致的，預設sample裡面是固定主裝置號，需要修改為動態分配裝置號。
問題3：動態分配主裝置號，如何知道分配主裝置是多少
答：cat /proc/devices 可以看到主裝置號的分配
附錄，單一裝置的驅動程式碼和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裝置結構體 */
struct globalmem_dev {
struct cdev cdev;
unsigned char mem[GLOBAMEM_SIZE];
};
struct globalmem_dev globalmem_devp;
/ 檔案開啟函式 */
int globalmem_open(struct inode *inode, struct file filp)
{
/ /
filp->private_data = globalmem_devp;
return 0;
}
/
int globalmem_release(struct inode *inode, struct file *filp)
{
return 0;
}
/* ioctl 裝置控制函式 */
static long globalmem_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
//
struct globalmem_dev dev = filp->private_data;/ 獲得裝置結構體指標 */
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;
}
/* 讀函式 */
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;/* 獲得裝置結構體指標 */
if (p >= GLOBAMEM_SIZE)
return 0;
if (count > GLOBAMEM_SIZE - p)
count = GLOBAMEM_SIZE - p;
/* 核心空間--> 使用者空間 */
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;/* 獲得裝置結構體指標 */
if (p >= GLOBAMEM_SIZE)
return 0;
if (count > GLOBAMEM_SIZE - p)
count = GLOBAMEM_SIZE - p;
/* 使用者空間--> 核心空間 */
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;/* 獲得裝置結構體指標 */
return ret;
}
/* 檔案操作結構體 */
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,
};
/* 初始化並註冊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);
}
/* 裝置驅動模組載入函式 /
int globalmem_init(void)
{
int result;
dev_t devno = MKDEV(globalmem_major, 0); / devno = (250<<20) | 0 */
/* 申請裝置號 */
if (globalmem_major)
result = register_chrdev_region(devno, 1, "globalmem");
else { /* 動態申請裝置號 */
result = alloc_chrdev_region(&devno, 0, 1, "globalmem");
globalmem_major = MAJOR(devno);
}
if (result < 0)
return result;
/* 動態申請裝置結構體的記憶體 */
globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);
if (!globalmem_devp) { /* 申請失敗 */
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;
}
/* 模組解除安裝函式 /
void globalmem_exit(void)
{
cdev_del(&globalmem_devp->cdev); / 登出CDEV /
kfree(globalmem_devp); / 釋放裝置結構體記憶體 /
unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); / 釋放裝置號 */
}
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`