On Fri, Sep 10, 2010 at 11:51 AM, fabio de francesco <fa...@metanix.org> 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 );
That will print the char 0 instead of the null char.
Second try using "dd if=[dev] count=1" instead to read.
--
John
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