Re: character device driver reading only last character of buffer

[Venkatram Tummala <venkatram867@xxxxxxxxx>]

On Sat, Sep 25, 2010 at 9:46 PM, Bond <jamesbond.2k.g@xxxxxxxxx> wrote:

On Sun, Sep 26, 2010 at 3:43 AM, Venkatram Tummala <venkatram867@xxxxxxxxx> wrote:

This will print the the last character of the string you  wrote.

If you would have read the thread from my first post printing the last character is not my objective  I am trying to print the complete string.

Yes, it is possible to pass in 0 for register_chrdev. Please be clear what you want to achieve, from your subject line & the post. The subject line  & the first few lines of the post indicates that  you need something which prints only the last character.  And you go on creating a rucus around here. I have updated the code & attached it. This can only read & write 10 characters. Now, please dont tell us that it is not you wanted or it doesn't work.  Please spare us.

As a side note, please spare us all with all this non-sense. We have better things to do in our life. Please try your level best to understand things before asking the kernel mailing list. If this BS continues, i am afraid you will get yourself kicked out of the mailing list. Please do yourself a favour by not posting such crap.

Venkatram Tummala

Please read the thread before giving a lecture on kernel newbies.

/* Necessary includes for device drivers */
#include <linux/init.h>
//#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_from/to_user */

MODULE_LICENSE("Dual BSD/GPL");

/* Declaration of memory.c functions */
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos);
void memory_exit(void);
int memory_init(void);

/* Structure that declares the usual file */
/* access functions */
struct file_operations memory_fops = {
	read: memory_read,
   	write: memory_write,
	open: memory_open,
	release: memory_release
};
/* Declaration of the init and exit functions */
module_init(memory_init);
module_exit(memory_exit);

/* Buffer to store data */
char *memory_buffer;
int result;

int memory_init(void) {

	/* Registering device */
	result = register_chrdev(0, "bond", &memory_fops);
	if (result < 0) {
		printk(KERN_ALERT  "memory: cannot obtain major number \n");
		return result;
	}

	/* Allocating memory for the buffer */
	memory_buffer = kmalloc(10, GFP_KERNEL); 
	if (!memory_buffer) { 
		result = -ENOMEM;
		goto fail; 
	} 
	memset(memory_buffer, 0, 10);

	printk(KERN_ALERT "Inserting bond module\n"); 
	return 0;

fail: 
	memory_exit(); 
	return result;
}


void memory_exit(void) {
	/* Freeing the major number */
	unregister_chrdev(result, "bond");

	/* Freeing buffer memory */
	if (memory_buffer) {
		kfree(memory_buffer);
	}

	printk( KERN_ALERT "Removing bond module\n");

}


int memory_open(struct inode *inode, struct file *filp) {

	/* Success */
	return 0;
}


int memory_release(struct inode *inode, struct file *filp) {

	/* Success */
	return 0;
}


ssize_t memory_read(struct file *filp, char __user *buf, 
		size_t count, loff_t *f_pos) 
{
	if (*f_pos > 0)
		return 0;
	if (count > strlen(memory_buffer))
		count = strlen(memory_buffer);
	copy_to_user(buf,memory_buffer,count);
	*f_pos = *f_pos + count;

	return count; 
}

ssize_t memory_write( struct file *filp, const char __user *buf,
		size_t count, loff_t *f_pos) 
{
	copy_from_user(memory_buffer, buf, count);
	return count;
}