Initial commit

Makefile

@@ -0,0 +1,14 @@
+obj-m      := one.o
+
+CURRENT = $(shell uname -r)
+KDIR = /lib/modules/$(CURRENT)/build
+PWD = $(shell pwd)
+
+
+default:
+	make -C $(KDIR) M=$(PWD) modules
+
+
+clean:
+	make -C $(KDIR) M=$(PWD) clean
+

one.c

@@ -0,0 +1,141 @@
+
+#include <linux/module.h> /* Needed by all modules */
+#include <linux/kernel.h> /* Needed for KERN_INFO */
+#include <linux/init.h> /* Needed for the macros */
+#include <linux/fs.h>
+#include <asm/uaccess.h> /* for put_user */
+
+
+#define DEVICE_NAME "one"
+
+
+static char outputchar = '1';
+/*
+* module_param(foo, int, 0000)
+* The first param is the parameters name
+* The second param is it's data type
+* The final argument is the permissions bits,
+* for exposing parameters in sysfs (if non−zero).
+* e.g. change outputchar to 'a' with "echo "97" > /sys/module/one/parameter/outputchar"
+*/
+module_param(outputchar, byte, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP );
+MODULE_PARM_DESC(outputchar, "Character that will be output by the device file");
+
+static int major; /* Major number assigned to our device driver */
+static int device_opened = 0;
+
+/*
+ * Prototypes − this would normally go in a .h file
+ */
+static int one_init(void);
+static void one_exit(void);
+static int one_open(struct inode *, struct file *);
+static int one_release(struct inode *, struct file *);
+static ssize_t one_read(struct file *, char *, size_t, loff_t *);
+static ssize_t one_write(struct file *, const char *, size_t, loff_t *);
+
+
+static struct file_operations fops = 
+  {
+  .owner = THIS_MODULE,
+  .read = one_read,
+  .write = one_write,
+  .open = one_open,
+  .release = one_release
+  };
+
+static int __init one_init(void)
+  {
+  printk(KERN_INFO "Hello World from module one\n");
+  
+  major = register_chrdev(0, DEVICE_NAME, &fops);
+  if (major < 0) 
+    {
+    printk(KERN_ALERT "Error in register_chrdev:%d\n", major);
+    return major;
+    }
+    
+  printk(KERN_INFO "I was assigned major number %d.\n", major);
+  printk(KERN_INFO "Execute \"mknod /dev/one c %d 0\" to create device file.\n", major);
+  return 0;
+  }
+
+
+static void __exit one_exit(void)
+  {
+  // Unregister the device
+  unregister_chrdev(major, DEVICE_NAME);
+  
+  printk(KERN_INFO "Goodbye World from module one\n");
+  }
+  
+/*
+ * Called when a process tries to open the device file, like
+ * "cat /dev/mycharfile"
+ */
+static int one_open(struct inode *inode, struct file *file)
+  {
+  if (device_opened)
+    return -EBUSY;
+  device_opened++;
+  return 0;
+  }
+  
+/*
+* Called when a process closes the device file.
+*/
+static int one_release(struct inode *inode, struct file *file)
+  {
+  device_opened--; /* We're now ready for our next caller */
+  return 0;
+  }
+
+/*
+ * Called when a process, which already opened the dev file, attempts to read from it.
+ */
+static ssize_t one_read( struct file *filp, /* see include/linux/fs.h */
+                            char *buffer, /* buffer to fill with data */
+                            size_t length, /* length of the buffer */
+                            loff_t * offset)
+{
+/*
+* Number of bytes actually written to the buffer
+*/
+int bytes_read = 0;
+// Copying data to the buffer
+int i;
+for (i = 0; i < length; i++)
+  {
+  /*
+  * The buffer is in the user data segment, not the kernel
+  * segment so "*" assignment won't work. We have to use
+  * put_user which copies data from the kernel data segment to
+  * the user data segment.
+  */
+  put_user(outputchar, buffer++);
+  bytes_read++;
+  }
+/*
+ * Most read functions return the number of bytes put into the buffer
+ * return 0 would signify end of file
+ */
+return bytes_read;
+}
+
+
+/*
+ * Called when a process writes to dev file: echo "hi" > /dev/hello
+ */
+static ssize_t one_write(struct file *filp, const char *buff, size_t len, loff_t * off)
+  {
+  printk(KERN_ALERT "Sorry, write isn't supported.\n");
+  return -EINVAL;
+  }
+
+
+module_init(one_init);
+module_exit(one_exit);
+
+MODULE_LICENSE("Some License");
+MODULE_AUTHOR("Matthias Janetschek"); /* Who wrote this module? */
+MODULE_DESCRIPTION("An example module"); /* What does this module do */