copy_to_user

[Hemanth Kumar]

--- On Thu, 23/12/10, Srinivas G. <srinivasg at esntechnologies.co.in> wrote:

> From: Srinivas G. <srinivasg at esntechnologies.co.in>
> Subject: RE: copy_to_user
> To: "Dexter Haslem" <dexter.haslem at gmail.com>, "Hemanth Kumar" <hemwire at yahoo.co.in>
> Cc: Kernelnewbies at kernelnewbies.org
> Date: Thursday, 23 December, 2010, 10:05 AM
> > On 12/22/2010 5:59 PM, Hemanth
> Kumar wrote:
> > > Hi All,
> > >
> > >         
>    I have small problem with copy_to_user in
> read
> > function,below is my code,when I try to read from
> userspace I get
> > segmentation fault,
> > > Can any please point me where I went wrong,
> 
> I guess, you need to also implement open method in your
> driver. Because,
> you are opening the device in your application. Could you
> try this?
> 
> Regards,
> Srinivas G

Hi Srinivas,

        I tried it,but with out any success,the same problem,

regards, 


 
> > >
> > >
> > > #include<linux/kernel.h>
> > > #include<linux/module.h>
> > > #include<linux/init.h>
> > > #include<linux/types.h>
> > > #include<linux/proc_fs.h>
> > > #include<linux/fs.h>
> > > #include<linux/kdev_t.h>
> > > #include<linux/jiffies.h>
> > > #include<linux/cdev.h>
> > > #include<asm/uaccess.h>
> > > #include<linux/mutex.h>
> > >
> > > struct mutex timer;
> > > static struct cdev my_cdev;
> > > dev_t devn;
> > > int maj = 300;
> > > int min = 0;
> > > int count = 1;
> > > char modname[] = "mytimer";
> > > short x[10] = {1,2,3,4,5,6,7,8,9,10};
> > >
> > >
> > >
> > >
> > > ssize_t my_read(struct file *file,char
> *buf,size_t count,loff_t
> > *pos){
> > >       unsigned long
> res;
> > >       void *k = (void
> *)&x;
> > >            void *l
> = (void *)&x+1;
> > >            void *j
> = (void *)&x+2;
> > >
> > >             
>      
>    mutex_lock(&timer);
> > >             
>              
>    res =
> > copy_to_user(buf,k,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,l,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,j,sizeof(short));
> > >
> > >             
>            /* 
>   res =
> > copy_to_user(buf,&x+4,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,&x+5,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,&x+6,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,&x+7,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,&x+8,sizeof(short));
> > >             
>              
>    res =
> > copy_to_user(buf,&x+9,sizeof(short));
> > >             
>             */
> > >             
>      mutex_unlock(&timer);
> > >
> > >     return 20;
> > >
> > > }
> > >
> > >
> > > static struct file_operations my_fops = {
> > >             
>      .owner = THIS_MODULE,
> > >             
>      .read = my_read,
> > >
> > > };
> > >
> > >
> > > static int __init my_init(void){
> > >          int ret;
> > >     devn = MKDEV(maj,min);
> > >
> > >       ret =
> register_chrdev_region(devn,count,modname);
> > >
> > >       
> cdev_init(&my_cdev,&my_fops);
> > >       
> cdev_add(&my_cdev,devn,count);
> > >
> > >       
> printk("<1>  Register timer maj = %d\n",maj);
> > >
> > >
> > >
> > >
> > >   return 0;
> > > }
> > >
> > >
> > >
> > > static void __exit my_exit(void){
> > >
> > >       
> cdev_del(&my_cdev);
> > >     
>    unregister_chrdev_region(devn,count);
> > >         
> printk("<1>  Bye Bye \n");
> > >
> > > }
> > >
> > >
> > > module_init(my_init);
> > > module_exit(my_exit);
> > > MODULE_LICENSE("Dual BSD/GPL");
> > >
> > >
> > >
> > >
> > > my userspace App:
> > >
> > > #include<stdio.h>
> > > #include<fcntl.h>
> > > #include<stdlib.h>
> > > #include<unistd.h>
> > >
> > > int main()
> > > {
> > >           int
> nbytes ;
> > >           char
> n[20];
> > >       
>    short a = *((short *)&n[0]);
> > >       
>    short b = *((short *)&n[2]);
> > >       
>    short c = *((short *)&n[4]);
> > >
> > >          int 
>    fd = open( "/dev/mytimer", O_RDONLY );
> > >          if (
> fd<  0 ) { perror( "/dev/mytimer" ); exit(1); }
> > >
> > > while ( 1 )
> > >             
>     {
> > >
> > >             
>      nbytes = read( fd, n, 40 );
> > >             
>     if ( nbytes<  0 ) break;
> > >
> > >             
>     printf( "\r a = %d \n ", a);
> > >             
>     printf("\r b = %d \n",b);
> > >             
>     printf("\r c = %d \n",c);
> > >
> > >             
>     sleep(1);
> > >             
>     fflush( stdout );
> > >             
>     }
> > > return 0;
> > > }
> > >
> > >
> > >
> > >
> > > Best regards,
> > >
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > Kernelnewbies mailing list
> > > Kernelnewbies at kernelnewbies.org
> > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> > Hi,
> > 
> > At first glance, you have char n[20], but read 40
> bytes in the read
> > call. char is only 1 byte on x86 I believe so that
> might be your
> > problem.
> > 
> > --
> > -Dexter Haslem
> > 
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>