--- On Thu, 23/12/10, Srinivas G. <srinivasg@xxxxxxxxxxxxxxxxxxxxx> wrote:
> From: Srinivas G. <srinivasg@xxxxxxxxxxxxxxxxxxxxx>
> Subject: RE: copy_to_user
> To: "Dexter Haslem" <dexter.haslem@xxxxxxxxx>, "Hemanth Kumar" <hemwire@xxxxxxxxxxx>
> Cc: Kernelnewbies@xxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxxxxxxxx
> > > 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@xxxxxxxxxxxxxxxxx
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
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