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/*
* iir.c: Creates a read-only char device that always gives you a random number
* iir stands for: infinite improbable randomness
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <asm/uaccess.h> /* for put_user */
/*
* Prototypes - this would normally go in a .h file
*/
int init_module(void);
void cleanup_module(void);
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 *);
#define SUCCESS 0
#define DEVICE_NAME "iir" /* Dev name as it appears in /proc/devices */
/*
* Global variables are declared as static, so are global within the file.
*/
static int Major; /* Major number assigned to our device driver */
static struct file_operations fops = {
.read = device_read,
.write = device_write,
.open = device_open,
.release = device_release
};
/*
* This function is called when the module is loaded
*/
int init_module(void)
{
Major = register_chrdev(0, DEVICE_NAME, &fops);
if (Major < 0) {
printk(KERN_ALERT "Registering char device failed with %d\n", Major);
return Major;
}
printk(KERN_INFO "infinite improbable randomness loaded (major number %d)\n", Major);
return SUCCESS;
}
/*
* This function is called when the module is unloaded
*/
void cleanup_module(void)
{
/*
* Unregister the device
*/
unregister_chrdev(Major, DEVICE_NAME);
printk(KERN_INFO "infinite improbable randomness unloaded\n");
}
/*
* Methods
*/
/*
* Called when a process tries to open the device file, like
* "cat /dev/mycharfile"
*/
static int device_open(struct inode *inode, struct file *file)
{
try_module_get(THIS_MODULE);
return SUCCESS;
}
/*
* Called when a process closes the device file.
*/
static int device_release(struct inode *inode, struct file *file)
{
/*
* Decrement the usage count, or else once you opened the file, you'll
* never get get rid of the module.
*/
module_put(THIS_MODULE);
return 0;
}
/*
* Called when a process, which already opened the dev file, attempts to
* read from it.
*/
static ssize_t device_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)
{
/*
* Actually put the data into the buffer
*/
size_t read = 0;
while (length) {
/*
* 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('9', buffer++);
length--;
read++;
}
/*
* Most read functions return the number of bytes put into the buffer
*/
return read;
}
/*
* Called when a process writes to dev file: echo "hi" > /dev/hello
*/
static ssize_t
device_write(struct file *filp, const char *buff, size_t len, loff_t * off)
{
if(!strncmp(buff, "are you really that random?", len)) {
printk(KERN_INFO "That's the problem with randomness, you can never be sure.\n");
return len;
}
return -EINVAL;
}
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