Subject: added another char driver(null-driver.c)

Description:

Author: psachin

test_char_device/Makefile

@@ -1,5 +1,7 @@
-# Makefile for testCharDevice.c
-obj-m := testCharDevice.o
+# Makefile for charater devices
+obj-m += testCharDevice.o
+obj-m += null-driver.o
+obj-m += video-ram.o
 
 KDIR=/usr/src/linux-headers-$(shell uname -r)
 

test_char_device/null-driver.c

@@ -0,0 +1,96 @@
+/* null-driver.c */
+/* 
+   Usage:
+
+   make
+   sudo insmod null-driver.ko
+   echo "some-text" > /dev/mynull
+   cat /dev/mynull
+   sudo rmmod null-driver.ko
+ */
+#include <linux/module.h>
+#include <linux/version.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/kdev_t.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/cdev.h>
+ 
+static dev_t first; // Global variable for the first device number 
+static struct cdev c_dev; // Global variable for the character device structure
+static struct class *cl; // Global variable for the device class
+static int my_open(struct inode *i, struct file *f)
+{
+  printk(KERN_INFO "Driver: open()\n");
+  return 0;
+}
+static int my_close(struct inode *i, struct file *f)
+{
+  printk(KERN_INFO "Driver: close()\n");
+  return 0;
+}
+static ssize_t my_read(struct file *f, char __user *buf, size_t
+		       len, loff_t *off)
+{
+  printk(KERN_INFO "Driver: read()\n");
+  return 0;
+}
+static ssize_t my_write(struct file *f, const char __user *buf,
+			size_t len, loff_t *off)
+{
+  printk(KERN_INFO "Driver: write()\n");
+  return len;
+}
+static struct file_operations pugs_fops =
+  {
+    .owner = THIS_MODULE,
+    .open = my_open,
+    .release = my_close,
+    .read = my_read,
+    .write = my_write
+  };
+
+static int __init ofcd_init(void) /* Constructor */
+{
+  printk(KERN_INFO "null-driver: ofcd registered");
+  if (alloc_chrdev_region(&first, 0, 1, "Shweta") < 0)
+    {
+      return -1;
+    }
+  if ((cl = class_create(THIS_MODULE, "chardrv")) == NULL)
+    {
+      unregister_chrdev_region(first, 1);
+      return -1;
+    }
+  if (device_create(cl, NULL, first, NULL, "mynull") == NULL)
+    {
+      class_destroy(cl);
+      unregister_chrdev_region(first, 1);
+      return -1;
+    }
+  cdev_init(&c_dev, &pugs_fops);
+  if (cdev_add(&c_dev, first, 1) == -1)
+    {
+      device_destroy(cl, first);
+      class_destroy(cl);
+      unregister_chrdev_region(first, 1);
+      return -1;
+    }
+  return 0;
+}
+ 
+static void __exit ofcd_exit(void) /* Destructor */
+{
+  cdev_del(&c_dev);
+  device_destroy(cl, first);
+  class_destroy(cl);
+  unregister_chrdev_region(first, 1);
+  printk(KERN_INFO "null-driver: ofcd unregistered");
+}
+ 
+module_init(ofcd_init);
+module_exit(ofcd_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Anil Kumar Pugalia <email_at_sarika-pugs_dot_com>");
+MODULE_DESCRIPTION("Our First Character Driver");

userapplication/userapp.c

@@ -2,7 +2,7 @@
 /* 
    Usage:
    % make
-   % ./userapp
+   % sudo ./userapp
  */
 #include<stdio.h>
 #include<stdlib.h>
@@ -18,7 +18,7 @@ int main(int argc, char *argv[])
   fd = open(DEVICE, O_RDWR);	/* open for read/write */
 
   if(fd == -1){
-    printf("file %s either doesnot exit, or locked by another process\n", DEVICE);
+    printf("file %s either does not exit, or locked by another process, or you are not root!\n", DEVICE);
     exit(-1);
   }
   printf("r - read from device,\nw- write from device\nEnter command: ");