Linux Driver -> insmod -> lsmod showing the driver, but no entry in /dev?

Question

just making my first steps in Linux Driver creation. Got this finally working:

#include <linux/version.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/uaccess.h>

#define DRIVER_AUTHOR "DirtyDiddy"
#define DRIVER_DESC "Ein Treiber der zuordnet Hexzahl -> Monatsname"

static unsigned int GM_major    = 0;
static unsigned int GM_minor    = 0;
static size_t count_w4proc  = 0;
static size_t count_r4proc  = 0;

MODULE_LICENSE("GPL");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);

/*Listing 15*/
int GM_read_proc(char* page, char** start, off_t offset, int count, int* eof, void* data)
{
    int len = 0, min;
    len = snprintf(page, count,     "Major number   = %d \n"
                    "Minor number   = %d \n"
                    "geschrieben    = %d \n"
                    "gelesen    = %d \n",
    GM_major, GM_minor, count_w4proc, count_r4proc);
    *eof = 1;
    min = (len > count ? count : len);
    return min;
}

/*Listing 16*/
int GM_open(struct inode* inode, struct file* filp)
{
    GM_minor = iminor(inode);
    printk(KERN_INFO "GM_open: Minor number = %d\n", GM_minor);
    return 0;
}

int GM_close(struct inode* inode, struct file* filp)
{
    printk(KERN_INFO "GM_close\n");
    return 0;
}

/*Listing 17*/
ssize_t GM_read(struct file* filp, char*buf, size_t count, loff_t* t)
{
    char kbuf[10];
    unsigned long not_copied;
    kbuf[0] =0x00;
    printk(KERN_INFO "gm_read: count = %d\n", count);
    not_copied = copy_to_user(buf, kbuf, 10);
    if(not_copied != 0) return (-EFAULT);
    count_r4proc++;
    return 10;
}

/*Listing 18*/
ssize_t GM_write(struct file* filp, char*buf, size_t count, loff_t* t)
{
    printk(KERN_INFO "gm_write: count = %d\n", count);
    count_r4proc++;
    return count;
}

/*Listing 19*/
struct file_operations GM_fops = {
.owner  = THIS_MODULE,
.read   = GM_read,
.write  = GM_write,
.open   = GM_open,
.release= GM_close
};

/*Listing 20*/
int init_module(void)
{
    int result;
    printk(KERN_INFO "init_module_gm\n");

    result = register_chrdev(GM_major, "GetMonth", &GM_fops);
    if(result < 0)
    {
        printk(KERN_INFO "GM_init_module: kein Zugriff auf Major number\n");
        return result;
    }
    printk(KERN_INFO "GM_init_module: register _chrdev ok\n");
    if(GM_major == 0) GM_major = result;
    printk(KERN_INFO "GM_init_module: Major number = %d \n", GM_major);

    create_proc_read_entry("GetMonth", 0, NULL, GM_read_proc, NULL);
    return 0;
}

/*Listing 21*/
void cleanup_module(void)
{
    printk(KERN_INFO "cleanup_module_gm : ungregister\n");
    unregister_chrdev(GM_major, "GetMonth");
    remove_proc_entry("GetMonth", NULL);
    printk(KERN_INFO "GM_cleanup: Ende \n");
}

Still testing, so content/purpose is not so important so far, but... After insmoding the GetMonth.ko, i could see it in the lsmod-List. I also saw the kprinft working and the /proc document.

But I was horrified not seeing anything oft my driver in /dev ?!

How cant that be? Doesn't every driver create a file in this directory?

Answer 1

No for you to have a driver in /dev directory you have to use mknod command. mknod /dev/<name> <char/block> <major-number> <minor-number>.

So this device driver created now will look up for major number in /proc/modules/ where the entry was made by insmod command.

You don't necessarily have to create device drivers in /dev/ but as a convention we use it.

Edit:

I like it thinking this way, when you load a kernel module it just sits there but when you create special file with mknod this is the file on which you operate and it uses the that loaded module to run. How does device file know which module we it should use? It decides that on the major number you provide to it.