Linux操作系统实验:模块编程

实验目的

• 编写一个内核模块；
• 编译该模块；
• 加载、卸载该模块；(相关命令： lsmod,insmod,rmmod,dmesg)

实验过程

编写内核模块代码

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
 
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robert W. Oliver II");
MODULE_DESCRIPTION("A simple example Linux module.");
MODULE_VERSION("0.01");
 #define DEVICE_NAME "lkm_example"#define EXAMPLE_MSG "Hello, World!\n"#define MSG_BUFFER_LEN 15
 /* Prototypes for device functions */static int device_open(struct inode *, struct file *);static int device_release(struct inode *, struct file *);static ssize_t device_read(struct file *, char *, size_t, loff_t *);static ssize_t device_write(struct file *, const char *, size_t, loff_t *);
 static int major_num;static int device_open_count = 0;static char msg_buffer[MSG_BUFFER_LEN];static char *msg_ptr;
 /* This structure points to all of the device functions */static struct file_operations file_ops = {
 .read = device_read,
 .write = device_write,
 .open = device_open,
 .release = device_release};
 /* When a process reads from our device, this gets called. */static ssize_t device_read(struct file *flip, char *buffer, size_t len, loff_t *offset) {
 int bytes_read = 0;
  /* If we’re at the end, loop back to the beginning */
  if (*msg_ptr == 0) {
   msg_ptr = msg_buffer;
  }
  /* Put data in the buffer */
  while (len && *msg_ptr) {
    /* Buffer is in user data, not kernel, so you can’t just reference
     * with a pointer. The function put_user handles this for us */
    put_user(*(msg_ptr++), buffer++);
    len--;
    bytes_read++;
 }
  return bytes_read;}
 /* Called when a process tries to write to our device */static ssize_t device_write(struct file *flip, const char *buffer, size_t len, loff_t *offset) {
 /* This is a read-only device */
  printk(KERN_ALERT "This operation is not supported.\n");
  return -EINVAL;}
 /* Called when a process opens our device */static int device_open(struct inode *inode, struct file *file) {
  /* If device is open, return busy */
  if (device_open_count) {
   return -EBUSY;
  }
  device_open_count++;
  try_module_get(THIS_MODULE);
  return 0;}
 /* Called when a process closes our device */static int device_release(struct inode *inode, struct file *file) {
  /* Decrement the open counter and usage count. Without this, the module would not unload. */
  device_open_count--;
  module_put(THIS_MODULE);
  return 0;}
 static int __init lkm_example_init(void) {
  /* Fill buffer with our message */
  strncpy(msg_buffer, EXAMPLE_MSG, MSG_BUFFER_LEN);
  /* Set the msg_ptr to the buffer */
  msg_ptr = msg_buffer;
  /* Try to register character device */
  major_num = register_chrdev(0, "lkm_example", &file_ops);
  if (major_num < 0) {
   printk(KERN_ALERT "Could not register device: %d\n", major_num);
   return major_num;
  } else {
   printk(KERN_INFO "lkm_example module loaded with device major number %d\n", major_num);
   return 0;
  }}
 static void __exit lkm_example_exit(void) {
  /* Remember — we have to clean up after ourselves. Unregister the character device. */
  unregister_chrdev(major_num, DEVICE_NAME);
  printk(KERN_INFO "Goodbye, World!\n");}
 /* Register module functions */
module_init(lkm_example_init);
module_exit(lkm_example_exit);

以上代码实现，当模块加载后，显示设备主要编号，卸载后显示“Goodbye, World”

问题与解决办法

Disagrees about version of symbol symbol_name after insmod

此处问题出现原因是linux模块与内核版本不同，通过modinfo和uname -a 比对后选择相同的linux模块，重新编译即可

编译

安装开发工具集合：

sudo apt-get install build-essential linux-headers-`uname -r`

编写Makefile

obj-m += lkm_example.o

all:

make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules

clean:

make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean

test:

  # We put a — in front of the rmmod command to tell make to ignore

  # an error in case the module isn’t loaded.

sudo rmmod lkm_example

  # Clear the kernel log without echo

sudo dmesg -C

  # Insert the module

sudo insmod lkm_example.ko

dmesg

编译模块

Sudo make

Sudo make test

执行成功后回显：

成功加载卸载模块

Lsmod | grep “lkm_example”

列出加载模块

实验心得

实验结论

本次实验已获得预期输出结果，但是在实验过程中却花费了不少的时间去学习相关知识与函数用法。

个人收获

通过这次小实验，让我进一步了解了linux如何编写内核模块，以及如何加载卸载编译内核模块，激起了我们对linux学习的兴趣