call_dev.c

linux device driver example

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>

#include <linux/fs.h>          
#include <linux/errno.h>       
#include <linux/types.h>       
#include <linux/fcntl.h>       

#define   CALL_DEV_NAME            "calldev"
#define   CALL_DEV_MAJOR            240      

int call_open (struct inode *inode, struct file *filp)
{
    int num = MINOR(inode->i_rdev); 

    printk( "call open -> minor : %d\n", num );

    return 0;
}

loff_t call_llseek (struct file *filp, loff_t off, int whence )
{
    printk( "call llseek -> off : %08X, whenec : %08X\n", off, whence );
    return 0x23;
}

ssize_t call_read(struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
    printk( "call read -> buf : %08X, count : %08X \n", buf, count );
    return 0x33;
}

ssize_t call_write (struct file *filp, const char *buf, size_t count, loff_t *f_pos)
{
    printk( "call write -> buf : %08X, count : %08X \n", buf, count );
    return 0x43;
}

int call_ioctl (struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{

    printk( "call ioctl -> cmd : %08X, arg : %08X \n", cmd, arg );
    return 0x53;
}

int call_release (struct inode *inode, struct file *filp)
{
    printk( "call release \n" );
    return 0;
}

struct file_operations call_fops =
{
    .owner    = THIS_MODULE,
    .llseek   = call_llseek,   
    .read     = call_read,     
    .write    = call_write,    
    .ioctl    = call_ioctl,    
    .open     = call_open,     
    .release  = call_release,  
};

int call_init(void)
{
    int result;

    printk( "call call_init \n" );    

    result = register_chrdev( CALL_DEV_MAJOR, CALL_DEV_NAME, &call_fops);
    if (result < 0) return result;

    return 0;
}

void call_exit(void)
{
    printk( "call call_exit \n" );    
    unregister_chrdev( CALL_DEV_MAJOR, CALL_DEV_NAME );
}

module_init(call_init);
module_exit(call_exit);

MODULE_LICENSE("Dual BSD/GPL");