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Old 02-24-2014, 10:06 AM   #1
rahil khera
LQ Newbie
 
Registered: Sep 2009
Posts: 14

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copy_from_user getting call infinite time in kernel level programming


I am trying following program.



Code:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/proc_fs.h>
#include<linux/sched.h>
#include <asm/uaccess.h>
#include <linux/slab.h>

int len,temp;
struct rw_semaphore sem;
char *msg;
size_t buffer_size= 0;
int read_proc(struct file *filp,char *buf,size_t count,loff_t *offp ) 
{

down_read(&sem);
//copy_to_user(buffer1,"In reader", 1024);
if(count > 1024)
{
	buffer_size = 1024;
}
else
{
	buffer_size = count;
}
copy_to_user(buf,msg,buffer_size);
up_read(&sem);   
return 0;
}

int write_proc(struct file *filp,const char *buf,size_t count,loff_t *offp)
{
down_write(&sem);
/*if(count > 1024)
{
	buffer_size = 1024;
}
else
{
	buffer_size = count;
}*/

//copy_to_user(buffer2,"In writer", 1024);
copy_from_user(msg,buf,buffer_size);
up_write(&sem);
return 0;
}

struct file_operations proc_fops = 
{
read: read_proc,
write: write_proc
};

void create_new_proc_entry() 
{
proc_create("hello1",0,NULL,&proc_fops);
msg=kmalloc(GFP_KERNEL,1024*sizeof(char));
//*msg = "PICT";
}

int proc_init (void) 
{
 create_new_proc_entry();
 init_rwsem(&sem);
 *msg = "PICT";
printk(KERN_INFO "msg :- %s \n", *msg);
 
 return 0;
}

void proc_cleanup(void) 
{
 remove_proc_entry("hello1",NULL);
}

MODULE_LICENSE("GPL"); 
module_init(proc_init);
module_exit(proc_cleanup);

After successfull make, when i try running cat /proc/hello1 command, it does not give any output and when i try running echo "hi" >> /proc/hello1 command, it goes into infinite loop and system gets dump.

Please tell me my mistake or how I should modify it to make it work.?
 
  


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kernel module, reader, semaphore, writer


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