--------------------
char_dev.c
--------------------
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h> // required for various structures related to files liked fops.
#include <asm/uaccess.h> // required for copy_from and copy_to user functions
#include <linux/semaphore.h>
#include <linux/cdev.h>
static int Major;
dev_t dev_no,dev;
struct device
{
char array[100];
struct semaphore sem;
}char_dev;
int open(struct inode *inode, struct file *filp)
{
printk(KERN_INFO "Inside open \n");
if(down_interruptible(&char_dev.sem)) {
printk(KERN_INFO " could not hold semaphore");
return -1;
}
return 0;
}
int release(struct inode *inode, struct file *filp)
{
printk (KERN_INFO "Inside close \n");
printk(KERN_INFO "Releasing semaphore");
up(&char_dev.sem);
return 0;
}
ssize_t read(struct file *filp, char *buff, size_t count, loff_t *offp)
{
unsigned long ret;
printk("Inside read \n");
ret = copy_to_user(buff, char_dev.array, count);
return ret;
}
ssize_t write(struct file *filp, const char *buff, size_t count, loff_t *offp)
{
unsigned long ret;
printk(KERN_INFO "Inside write \n");
ret = copy_from_user(char_dev.array, buff, count);
return count;
}
struct file_operations fops = {
read: read,
write: write,
open: open,
release: release
};
struct cdev *kernel_cdev;
int char_dev_init (void)
{
int ret;
kernel_cdev = cdev_alloc();
kernel_cdev->ops = &fops;
kernel_cdev->owner = THIS_MODULE;
printk (" Inside init module\n");
ret = alloc_chrdev_region( &dev_no , 0, 1,"chr_arr_dev");
if (ret < 0) {
printk("Major number allocation is failed\n");
return ret;
}
Major = MAJOR(dev_no);
dev = MKDEV(Major,0);
sema_init(&char_dev.sem,1);
printk (" The major number for your device is %d\n", Major);
ret = cdev_add( kernel_cdev,dev,1);
if(ret < 0 )
{
printk(KERN_INFO "Unable to allocate cdev");
return ret;
}
return 0;
}
void char_dev_cleanup(void)
{
printk(KERN_INFO " Inside cleanup_module\n");
cdev_del(kernel_cdev);
unregister_chrdev_region(Major, 1);
}
MODULE_LICENSE("GPL");
module_init(char_dev_init);
module_exit(char_dev_cleanup);
-------------
Makefile :
-------------
ifneq ($(KERNELRELEASE),)
obj-m := char_dev.o
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif
----------------
creating a node:
----------------
mknod /dev/char_dev c 250 0
User Application :-
-------------------
main.c
------------------
#include <stdio.h>
#include <fcntl.h>
main ( )
{
int i,fd;
char ch, write_buf[100], read_buf[100];
fd = open("/dev/char_dev", O_RDWR);
if (fd == -1)
{
printf("Error in opening file \n");
exit(-1);
}
printf ("Press r to read from device or w to write the device ");
scanf ("%c", &ch);
switch (ch) {
case 'w':
printf (" Enter the data to be written into device");
scanf (" %[^\n]", write_buf);
write(fd, write_buf, sizeof(write_buf));
break;
case 'r':
read(fd, read_buf, sizeof(read_buf));
printf ("The data in the device is %s\n", read_buf);
break;
default:
printf("Wrong choice \n");
break;
}
close(fd);
}
------------------------------
Compiling User Application :
------------------------------
$gcc -o main main.c
#./main
Press r to read from device or w to write the device : w
Enter the data to be written into device : American Megatrends Inc.
#./main
Press r to read from device or w to write the device : r
The data in the device is : American Megatrends Inc.
char_dev.c
--------------------
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h> // required for various structures related to files liked fops.
#include <asm/uaccess.h> // required for copy_from and copy_to user functions
#include <linux/semaphore.h>
#include <linux/cdev.h>
static int Major;
dev_t dev_no,dev;
struct device
{
char array[100];
struct semaphore sem;
}char_dev;
int open(struct inode *inode, struct file *filp)
{
printk(KERN_INFO "Inside open \n");
if(down_interruptible(&char_dev.sem)) {
printk(KERN_INFO " could not hold semaphore");
return -1;
}
return 0;
}
int release(struct inode *inode, struct file *filp)
{
printk (KERN_INFO "Inside close \n");
printk(KERN_INFO "Releasing semaphore");
up(&char_dev.sem);
return 0;
}
ssize_t read(struct file *filp, char *buff, size_t count, loff_t *offp)
{
unsigned long ret;
printk("Inside read \n");
ret = copy_to_user(buff, char_dev.array, count);
return ret;
}
ssize_t write(struct file *filp, const char *buff, size_t count, loff_t *offp)
{
unsigned long ret;
printk(KERN_INFO "Inside write \n");
ret = copy_from_user(char_dev.array, buff, count);
return count;
}
struct file_operations fops = {
read: read,
write: write,
open: open,
release: release
};
struct cdev *kernel_cdev;
int char_dev_init (void)
{
int ret;
kernel_cdev = cdev_alloc();
kernel_cdev->ops = &fops;
kernel_cdev->owner = THIS_MODULE;
printk (" Inside init module\n");
ret = alloc_chrdev_region( &dev_no , 0, 1,"chr_arr_dev");
if (ret < 0) {
printk("Major number allocation is failed\n");
return ret;
}
Major = MAJOR(dev_no);
dev = MKDEV(Major,0);
sema_init(&char_dev.sem,1);
printk (" The major number for your device is %d\n", Major);
ret = cdev_add( kernel_cdev,dev,1);
if(ret < 0 )
{
printk(KERN_INFO "Unable to allocate cdev");
return ret;
}
return 0;
}
void char_dev_cleanup(void)
{
printk(KERN_INFO " Inside cleanup_module\n");
cdev_del(kernel_cdev);
unregister_chrdev_region(Major, 1);
}
MODULE_LICENSE("GPL");
module_init(char_dev_init);
module_exit(char_dev_cleanup);
-------------
Makefile :
-------------
ifneq ($(KERNELRELEASE),)
obj-m := char_dev.o
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif
----------------
creating a node:
----------------
mknod /dev/char_dev c 250 0
User Application :-
-------------------
main.c
------------------
#include <stdio.h>
#include <fcntl.h>
main ( )
{
int i,fd;
char ch, write_buf[100], read_buf[100];
fd = open("/dev/char_dev", O_RDWR);
if (fd == -1)
{
printf("Error in opening file \n");
exit(-1);
}
printf ("Press r to read from device or w to write the device ");
scanf ("%c", &ch);
switch (ch) {
case 'w':
printf (" Enter the data to be written into device");
scanf (" %[^\n]", write_buf);
write(fd, write_buf, sizeof(write_buf));
break;
case 'r':
read(fd, read_buf, sizeof(read_buf));
printf ("The data in the device is %s\n", read_buf);
break;
default:
printf("Wrong choice \n");
break;
}
close(fd);
}
------------------------------
Compiling User Application :
------------------------------
$gcc -o main main.c
#./main
Press r to read from device or w to write the device : w
Enter the data to be written into device : American Megatrends Inc.
#./main
Press r to read from device or w to write the device : r
The data in the device is : American Megatrends Inc.
