Linux 2.6.25 /dev entry problem

[errakeshpillai]

Hi all, I am making a small test device driver which will allocate 64 bytes of memory and allow to read/write the memory bytes. When I load the device driver using insmod, I'm getting the /sys/class and /proc entries properly, but the /dev entry is missing.

I googled about this but all the answers I found suggest the use of mknod to create the /dev node ourself. My requirement is that the /dev node also should be created automatically when we load the driver using insmod.

static char *g_mem_buff;
static struct mutex rw_lock;
static struct proc_dir_entry *proc_mem,*config_mem;
static int dev_major,dev_init_status;
static struct class *cl_mem;
static struct proc_dir_entry *mem_proc;

static int mem_driver_init(void);
static void mem_driver_exit(void);
static int mem_driver_open(struct inode *in, struct file *fp);
static int mem_driver_release(struct inode *in, struct file *fp);

static int __init mem_driver_init(void)
{
        struct device *mem_dev;
        return_t ret;

        printk(KERN_INFO "Initializing Driver.\n");

        /* Register the driver. */
        printk(KERN_INFO "Registering Memory Driver.\n");
        dev_major = register_chrdev (0,DEV_ENTRY,&mem_fops);
        if(dev_major < 0){
                printk(KERN_INFO "Driver registeration failed.\n");
                return dev_major;
        }
        printk(KERN_NOTICE "My driver registered successfully with major number: %d\n",dev_major);

        /* Reserving memory for the buffer. */
        g_mem_buff = kmalloc(BUFF_SIZE,GFP_KERNEL);
        if(!g_mem_buff){
                ret = EKMALLOC;
                goto mem_failed;
        }
        memset(g_mem_buff,0,BUFF_SIZE);
        printk(KERN_INFO "Mem Driver: Memory allocated and cleared.\n");

        /* Mutex Initialization. */
        mutex_init(&rw_lock);

        /* creating /sys/class interface */
        cl_mem = class_create(THIS_MODULE,CLASS_NAME);
        if(cl_mem == NULL){
                printk(KERN_NOTICE "Class creation failed.\n");
                ret = ECLASS_CREATE;
                goto class_failed;
        }
        printk(KERN_EMERG "Class created successfully.\n");

        /* Creating /dev interface. */
        mem_dev = device_create(cl_mem, NULL,MKDEV(dev_major,0), DEV_ENTRY);
        if(mem_dev == NULL){
                printk(KERN_NOTICE "Creating device node failed.\n");
                ret = EDEV_CREATE;
                goto dev_failed;
        }
        printk(KERN_EMERG "Dev node created successfully.\n");

        /* Creating /proc interface. */
      proc_ipmac = proc_mkdir("Dev_IPMAC",NULL);
        if(proc_ipmac == NULL){
                printk(KERN_NOTICE "Creating proc entry failed.\n");
                ret = EPROC_DIR_CREATE;
                goto proc_dir_failed;
        }

        mem_proc = create_proc_entry(PROC_ENTRY,0666,NULL);
        if(mem_proc == NULL){
                printk(KERN_NOTICE "My driver: Config proc failed.\n");
                ret = EPROC_CREATE;
                goto proc_entry_failed;
        }
        printk(KERN_INFO "My Driver: Proc init success.\n");

    mem_proc->read_proc = mem_read_proc;
        mem_proc->write_proc = mem_write_proc;

   dev_init_status = SUCCESS;
        return dev_init_status;

proc_entry_failed:
                device_destroy(cl_mem,MKDEV(dev_major,0));
dev_failed:
                class_destroy(cl_mem);
class_failed:
                kfree(g_mem_buff);
mem_alloc_failed:
                unregister_chrdev(dev_major,DEV_ENTRY);

        printk("Mem Driver: Driver unregistered.\n");

        dev_init_status = ret;
        return dev_init_status;
}

 

[Vengateswaran]

Hope this link will be helpful for creating the device node during insertion.
https://stackoverflow.com/questions/5970595/create-a-device-node-in-code

 

[errakeshpillai]

Thanx for answering..

I have used the same method and tried a lot of "googling" about this, but in vain.
I have to use mknod, don't know why..?

I have 2 drivers, one which will successfully creating the dev entry, but my driver with the similar flow of coding and functions is not creating the dev entry.

 

[Vengateswaran]

oK,Then... Whether u are able to create a dev entry using mknod.??

 

[errakeshpillai]

Yes, using mknod I'm able to create the dev node.

 

[Vengateswaran]

Ok then.. I think there may be problem in linking the file using insmod.

 

[errakeshpillai]

What kind of error with insmod. So how to solve that..?

Also if I use printk messages then the log messages are delivered correctly. "Device node created success" etc.....

 

[Vengateswaran]

Printk works.. I'm saying that there maybe linking problem in any other kernel modules when you r trying to create a dev node using insmod...

 

[errakeshpillai]

ok... I'll check that out..