驱动编写及编译例子

通用驱动程序基于globalmem共享内存的驱动编写write、read、ioctl、lseek函数globalmem.c

#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>

#define GLOBALMEM_SIZE 0x1000  /*全局内存最大4KB*/
#define MEM_CLEAR 0x1 /*清零全局内存*/
#define GLOBALMEM_MAJOR 250 /*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;
  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 0;
  if (count > GLOBALMEM_SIZE - p)
     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 {
     *ppos += count;
     ret = count;

     printk(KERN_INFO "read %u bytes(s) from %lu\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 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 %u bytes(s) from %lu\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)
 {
   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);
 
 /* 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("Barry Song <21cnbao@gmail.com>");
 MODULE_LICENSE("Dual BSD/GPL");
  
 module_param(globalmem_major, int, S_IRUGO);
 
 module_init(globalmem_init);
 module_exit(globalmem_exit);

驱动编译Makefile：

$(warning KERNELRELEASE=$(KERNELRELEASE))

ifeq ($(KERNELRELEASE),)

KERNELDIR ?= /home/tom/fs2416/linux-2.6.39-FS2416
PWD := $(shell pwd)

modules:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

modules_install:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install

clean:
    rm -rf *.o core *.ko *~ .depend .*.cmd *.mod.c .tmp_versions Module* modules*

.PHONY:
    modules modules_install clean

else
    obj-m := globalmem.o
endif

其中：$(MAKE) -C $(KERNELDIR) M=$(PWD) modules 的操作：$(MAKE) -C $(KERNELDIR)进入内核源码目录下执行主Makefile，其中会定义KERNELRELEASE常量；M=$(PWD) modules进入当前目录，执行当前目录下的Makefile，生产模块；
-C是表示进入$(KERNELDIR)目录执行makefile，M指定要生成的外部模块的目录。

Use make M=dir to specify directory of external module to build