--- On Thu, 23/12/10, Dexter Haslem <dexter.haslem@xxxxxxxxx> wrote:
> From: Dexter Haslem <dexter.haslem@xxxxxxxxx>
> Subject: Re: copy_to_user
> To: "Hemanth Kumar" <hemwire@xxxxxxxxxxx>
> Cc: Kernelnewbies@xxxxxxxxxxxxxxxxx
> Date: Thursday, 23 December, 2010, 6:48 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,
> >
> >
> > #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.
Hi Dexter,
I have commented remaining copy_to_user read function , it should be 6bytes,
> --
> -Dexter Haslem
>
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