Linux driver with new kernel-3.8

It took a long time to program the Linux character device for the first time today. The problems found are as follows:

Note the following:

1. the compiling module does not need to compile the kernel. Compile the device module in Ubuntu as follows:

2. After insmod, you need to use mknod for device ing. In this case, check the value of the master device in CAT/proc/devices.

Example: mknod/dev/TFS 250 0

3. When writing test code, pay attention to the use of permissions, because only the root permission is allowed to perform RW for permissions mapped to/dev/TFS. Other permissions are read-only.

First, attach the source code of the character device driver:

#include <linux/module.h>#include <linux/init.h>#include <linux/kernel.h>#include <linux/fs.h>#include <linux/errno.h>#include <asm/uaccess.h>#include <linux/slab.h>MODULE_LICENSE("Dual BSG/GPL");unsigned int fs_major = 0;static char *data;static ssize_t test_read(struct file *file, char *buf, size_t count, loff_t *f_pos);static ssize_t test_write(struct file *file, const char *buffer, size_t count, loff_t *f_pos);static int test_open(struct inode *inode, struct file *file);static int test_release(struct inode *inode, struct file *file);int init_module(void);void cleanup_module(void);static struct file_operations chr_fops = {read:test_read,write:test_write,open:test_open,release:test_release };static ssize_t test_read(struct file *file, char *buf, size_t count, loff_t *f_pos){int len;if (count<0)return -EINVAL;len = strlen(data);if (len<count)count = len;copy_to_user(buf, data, count+1);return count;}static ssize_t test_write(struct file *file, const char *buffer, size_t count, loff_t *f_pos){if (count < 0 )return -EINVAL;kfree(data);data = (char *) kmalloc(sizeof(char)*(count+1), GFP_KERNEL);if (!data)return -ENOMEM;copy_from_user(data, buffer, count+1);return count;}static int test_open(struct inode *inode, struct file *file){try_module_get(THIS_MODULE); printk("This is open \n");return 0;}static int test_release(struct inode *inode, struct file *file){module_put(THIS_MODULE);  printk("This is released\n");return 0;}int init_module(void){int res;res = register_chrdev(0, "tfs", &chr_fops);if (res<0){printk("Can't get major name\n");return 0;}if (fs_major == 0)fs_major=res;printk("Major name is %d", fs_major);return 0;}void clean_module(void){unregister_chrdev(fs_major, "tfs");printk("tfs has removed");}

The source code of makefile is attached. (make sure that the makefile is case-sensitive and cannot be makefile)

obj-m +=memrw_drv.oall:make -C /lib/modules/`uname -r`/build M=$(PWD) modulesclean:make -C /lib/modules/`uname -r`/build M=$(PWD) clean 

The test source code of the character device is attached:

#include <unistd.h>#include <stdio.h>#include <stdlib.h>#include <fcntl.h>#include <string.h>#define DEVPATH"/dev/tfs"int main(int argc, char **argv){int fd, i, nwrite, nread, len;char *buf = "String to Driver\n";char read_buf[18] = { 0 };fd = open(DEVPATH, O_RDWR);if (fd<0){perror("open");exit(1);}elseprintf("device opened!\n");fflush(stdout);len = strlen(buf);nwrite = write(fd, buf, len);if(nwrite<0){perror("write");exit(1);}nread = read(fd, read_buf, 18);if(nread<0){perror("read");exit(1);}elseprintf("Read String is from driver -> %s" , read_buf);fflush(stdout);close(fd);return 0;}