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barunparichha 02-15-2013 07:30 AM
CHAR driver's open function issue
 
I have written my sample char driver code where a dynamic device node /dev/testNode is created and I am trying to open this from a program in user space. But I am not getting "DEVICE OPENED ...." message in my log. So I am not sure if my open function "myopen" is called.
And help will be appreciated.


test.c :
Code:
#include<linux/module.h>
#include<linux/init.h>
#include<linux/fs.h>
#include<linux/cdev.h>
#include<linux/delay.h> //msleep
#include<linux/device.h> //device_create

#define COUNT 1
#define NAME "testNode"
static struct class *cl;
static struct cdev *cdev;
dev_t dev;


int myopen(struct inode *inode, struct file *file)
{
        int minor=MINOR(inode->i_rdev);
        int major=MAJOR(inode->i_rdev);
        printk(KERN_ALERT "DEVICE OPENED : major=%d minor=%d",major, minor);
        msleep(1);
        return 0;
}

static struct file_operations fops = {
        .owner=THIS_MODULE,
        .open=myopen,
};

static int start()
{
        int res;
        res=alloc_chrdev_region(&dev, 0, COUNT, NAME);
if(res <0)
        {
                printk(KERN_ALERT "Unable to allocate space");
                return res;
        }
        else
                printk(KERN_ALERT " Got Major=%d Minor=%d", MAJOR(dev), MINOR(dev));

        cdev = cdev_alloc();
        cdev->owner=THIS_MODULE;
        cdev->ops=&fops;
        res=cdev_add(cdev, dev, COUNT);

        //Creating device node for major number we got
        cl = class_create(THIS_MODULE,NAME);
        if(IS_ERR(cl))
        {
                printk(KERN_ALERT "device class NOT created ...");
                unregister_chrdev_region(cdev->dev,COUNT);
                cdev_del(cdev);
                return -1;
        }
        else
                printk(KERN_ALERT "device class created ...");

        if (device_create(cl, NULL, cdev->dev, NULL, NAME) ==NULL)
        {
                class_destroy(cl);
                unregister_chrdev_region(cdev->dev,COUNT);
                return -1;
        }

        printk(KERN_ALERT "START MODULE ...");
return 0;
}


static void leave()
{
        printk(KERN_ALERT "LEAVING MODULE ... %d %d",MAJOR(cdev->dev),MINOR(cdev->dev));
        device_destroy(cl, dev);
        class_destroy(cl);
        cdev_del(cdev);
        unregister_chrdev_region(cdev->dev,COUNT);
}


module_init(start);
module_exit(leave);
MODULE_LICENSE("GPL");
MODULE_OWNER("Barun Kumar Parichha");
Makefile:
Code:
obj-m +=test.o
all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
My User space C code to open /dev/testNode:
Code:
#include<stdio.h>

int main()
{
        FILE * fd;
        fd=fopen("/dev/testNode","r");
        if(fd <0)
        {
                printf("\nError opening node ");
                perror("fopen");
                return 0;
        }
        else
                printf("\n SUCCESS");

        return 0;
}

smallpond 02-17-2013 12:50 PM
Your code looks pretty good. The only thing I see missing is "\n" on the end of the printk's.

sanupdas 02-18-2013 02:53 AM
the code seems all perfect to me. i have tried it in my laptop running ubuntu 12.04 and its showing DEVICE OPENED when checking through dmesg command. may be some other issue wid you like permission.

barunparichha 02-18-2013 11:32 PM
Actually I have only sudo permision (not root) in my machine.
But when I tried with low level system calls (open/read/write), it works perfectly.

Code:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <stdlib.h>
#include <stdio.h>

int main() {

        int fh=-1;
        char buffer[65];
        int gotten;

        fh = open("/dev/testNode",O_RDWR|O_APPEND);
        if(fh >=0)
                printf ("File handle %d\n",fh);
        else
        {
                printf("Unable to open file");
                perror("open");
                return 0;
        }

        gotten = read(fh,buffer,64);
        if(gotten >0)
        {
                buffer[gotten] = '\0';
                printf("******%s",buffer);
        }
}
Thanks for looking into my code.


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