On Friday 10 September 2010 20:23:13 Josh Cartwright wrote:
> On Fri, Sep 10, 2010 at 05:51:41PM +0200, fabio de francesco wrote:
> > 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);
> >
> > return nbytes;
> >
> > }
>
> I'm not going to flat out answer your query, but help you work towards
> the solution yourself.
>
> Think about the termination case. In order to terminate, you'll need to
> return 0 to signal an end of file to the user-mode read.
>
> In what case could your code return 0?
I think I now see your point... Here is the mycdrv_read() function modified:
static ssize_t
mycdrv_read (struct file *file, char __user * buf, size_t lbuf, loff_t * ppos)
{
char *kbuf = file->private_data;
long nbytes, maxbytes, bytes_to_do;
maxbytes = KBUF_SIZE - *ppos;
bytes_to_do = lbuf < maxbytes ? lbuf : maxbytes;
(long)*ppos, maxbytes, bytes_to_do);
nbytes = bytes_to_do - copy_to_user (buf, kbuf + *ppos, bytes_to_do);
*ppos += nbytes;
return nbytes;
}
I think now it is working. What do you think about it?
Anyway I have another problem. I suppose the write function doesn't work
because after a writing with a "echo" I don't read anything with "cat":
static ssize_t
mycdrv_write (struct file *file, const char __user * buf, size_t lbuf,
loff_t * ppos)
{
char *kbuf = file->private_data;
long nbytes, maxbytes, bytes_to_do;
maxbytes = KBUF_SIZE - *ppos;
bytes_to_do = lbuf < maxbytes ? lbuf : maxbytes;
nbytes = bytes_to_do - copy_from_user (kbuf + *ppos, buf, lbuf);
*ppos += nbytes;
printk (KERN_INFO "\n WRITING function, nbytes=%ld, pos=%ld\n", nbytes,
(long)*ppos);
return nbytes;
}
Can you please help with this too?
Thanks in advance.
fabio
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