On Saturday 11 September 2010 12:04:37 fabio de francesco wrote:
> 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
I have also reworked the write() function following what I have done to the
read() one:
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, bytes_to_do );
*ppos += nbytes;
printk (KERN_INFO "\n WRITING function, nbytes=%ld, pos=%ld\n", nbytes,
(long)*ppos);
return nbytes;
}
Unfortunatelly I still can't read back what I have echoed to the device. I
don't understand whether the bug is still in the read() function or the
write() one.
fabio
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