On Friday 10 September 2010 19:02:09 John Mahoney wrote:
> On Fri, Sep 10, 2010 at 11:51 AM, 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:
> >
> > #include <linux/module.h> /* for modules */
> > #include <linux/fs.h> /* file_operations */
> > #include <linux/uaccess.h> /* copy_(to,from)_user */
> > #include <linux/init.h> /* module_init, module_exit */
> > #include <linux/slab.h> /* kmalloc */
> > #include <linux/cdev.h> /* cdev utilities */
> >
> > #define MYDEV_NAME "mycdrv"
> > #define KBUF_SIZE (size_t)( PAGE_SIZE )
> >
> > static char *kbuf;
> > static dev_t first;
> > static unsigned int count = 1;
> > static int my_major = 700, my_minor = 0;
> > static struct cdev *my_cdev;
> > static int counter = 0;
> >
> > static int mycdrv_open (struct inode *inode, struct file *file)
> > {
> > printk( KERN_INFO " open #%d\n", ++counter );
> > kbuf = kmalloc (KBUF_SIZE, GFP_KERNEL);
> > memset( kbuf, '\0', KBUF_SIZE );
>
> First this should be
> memset( kbuf, '0', KBUF_SIZE );
Ok. Please, why can't I pad the buffer with null bytes? Why '0' (zero
character) and not '\0' (null byte)?
>
> That will print the char 0 instead of the null char.
>
> Second try using "dd if=[dev] count=1" instead to read.
I just want the device to be read any means the user prefers, i.e. with "cat".
fabio
>
> --
> John
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