On Friday 10 September 2010 18:07:03 Daniel Baluta wrote:
> On Fri, Sep 10, 2010 at 6:51 PM, fabio de francesco <fabio@xxxxxxxxxxx>
wrote:
> > Hi all,
> >
> > I have modified a simple character device driver as an exercise from the
> > Cooperstein's Linux Device Drivers book.
> >
> > It seems to work fine except that when I "cat /dev/mycdrv" it provides
> > garbage.
> >
> > This is a trimmed down version of the code:
> >
> > [skipped]
> >
> > static ssize_t
> > mycdrv_read (struct file *file, char __user * buf, size_t lbuf, loff_t *
> > ppos) {
> > int nbytes, maxbytes, bytes_to_do;
> > maxbytes = KBUF_SIZE - *ppos;
> > bytes_to_do = lbuf <= maxbytes ? lbuf : maxbytes;
> > nbytes = lbuf - copy_to_user (buf, kbuf + *ppos, bytes_to_do);
> > *ppos += nbytes;
> > printk (KERN_INFO "\n READING function, nbytes=%d, pos=%d\n", nbytes,
> > (int)*ppos);
>
> Can you post the output of this line?
Sep 10 18:14:50 host11 kernel: READING function, nbytes=32768, pos=32768
Sep 10 18:14:50 host11 kernel:
Sep 10 18:14:50 host11 kernel: READING function, nbytes=32768, pos=65536
Sep 10 18:14:50 host11 kernel:
Sep 10 18:14:50 host11 kernel: READING function, nbytes=32768, pos=98304
Sep 10 18:14:50 host11 kernel:
Sep 10 18:14:50 host11 kernel: READING function, nbytes=32768, pos=131072
It goes on for tens of lines... I can't understand.
> > return nbytes;
> > }
> >
> > [skipped]
> >
> > Please, could someone explain why the readings of the device return
> > garbage data instead of NULL characters as I have set with memset()?
--
To unsubscribe from this list: send an email with
"unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
Please read the FAQ at http://kernelnewbies.org/FAQ
