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,
>
>
>
>
>
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> 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
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