Character device driver problem

[Siddharth Taneja <taneja@xxxxxxx>]

Hi,

I am trying to build a simple character device driver which supports 
only the open, read and release interface. The code compiles fine and 
the module gets inserted also fine but when I do cat <device name>, the 
read function is entered multiple times, resulting in multiple and same 
outputs("we did it" repeated continously). I am using Suse 9.2 with 
kernel 2.6.8-24.11. The following is the code and outputs.

Thanks

Siddharth


//Building a character device driver

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

static int Major;
static int devOpen;
static char msg[80];
static char*msgPtr;
static int moduleOpen(struct inode *,struct file *);
static ssize_t moduleRead(struct file *,char *,size_t,loff_t *);
static int moduleRelease(struct inode *,struct file *);

#define DEV_NAME "myModule"

static struct file_operations fops = {
   .read=moduleRead,
   .open=moduleOpen,
   .release=moduleRelease
};

int startup(void) {
   printk(KERN_EMERG "I am in\n");
   devOpen=0;
   Major=register_chrdev(0,DEV_NAME,&fops);
   if (Major <0) {
       printk(KERN_EMERG "wtf!?\n");
       return Major;
   }
   printk(KERN_EMERG "Heres ur maj no:%d\n",Major);
   return 0;
}


void cleanup(void) {
   printk(KERN_EMERG "Have to go..\n");
   unregister_chrdev(Major,DEV_NAME);
}

static int moduleOpen(struct inode *in,struct file *fi) {
   if(devOpen==1)
       return -EBUSY;
   devOpen++;
   sprintf(msg,"we did it");
   msgPtr=msg;
   printk(KERN_EMERG "Open seeeaa..\n");
   return 0;
}

static ssize_t moduleRead(struct file *fi,char *buff, size_t len, loff_t 
* offs){
   static int cnt=8;
   printk(KERN_EMERG "Reading %d\n",len);

   while(cnt>=0&&len) {
       put_user(*msgPtr,buff);
       msgPtr++;
       buff++;
       cnt--;
   }
   //put_user('\0',buff);
   return len;
}

static int moduleRelease(struct inode *in,struct file* fi) {
   printk(KERN_EMERG "Release me...\n");
   devOpen--;
   return 0;
}

module_init(startup);
module_exit(cleanup);
MODULE_LICENSE("GPL and additional rights");

--------------------------------------------------------------------------------------------------------------------------------------------------

Output (log messages)

Mar 21 01:19:32 linux kernel: module first_module unsupported by 
SUSE/Novell, tainting kernel.
Mar 21 01:19:32 linux kernel: I am in
Mar 21 01:19:32 linux kernel: Heres ur maj no:253
Mar 21 01:19:46 linux kernel: Open seeeaa..
Mar 21 01:19:46 linux kernel: Reading 4096
Mar 21 01:19:46 linux last message repeated 177 times
Mar 21 01:19:46 linux kernel: Release me...
Mar 21 01:19:56 linux kernel: Have to go..





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