Re: [PATCH 1/1] UIO: Add a write() function to enable/disable interrupts

Hans J. Koch
2008-05-23T22:44:21Z

On Fri, May 23, 2008 at 10:44:42PM +0200, Leon Woestenberg wrote:
> Hello,
>
> On Fri, May 23, 2008 at 1:55 PM, Hans J. Koch <hjk@linutronix.de> wrote:
> > +static ssize_t uio_write(struct file *filep, const char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + struct uio_listener *listener = filep->private_data;
> > + struct uio_device *idev = listener->dev;
> > + ssize_t retval;
> > + s32 irq_on;
> > +
> > + if (idev->info->irq == UIO_IRQ_NONE)
> > + return -EIO;
> > +
> > + if (count != sizeof(s32))
> > + return -EINVAL;
> > +
> > + if (!idev->info->irqcontrol)
> > + return -ENOSYS;
> > +
> > + if (copy_from_user(&irq_on, buf, count))
> > + return -EFAULT;
> > +
> > + retval = idev->info->irqcontrol(idev->info, irq_on);
> > +
> > + return retval ? retval : sizeof(s32);
> > +}
> > +
>
> Shouldn't this be more future-proof, what if we need to abuse write()
> for something else in the future?

We don't. I'm thinking about letting the function fail if irq_on is not
0 or 1, just to stop any ideas of abusing write().

read() and write() only deal with irq handling, all data exchange with the
device is done through mapped memory.

>
> I would suggest a check for ppos to be 0 (zero) as well, just to be
> sure and future-proof and backwards-safe.

write() is only for enabling/disabling irqs, there's only one possible
value of count, and we don't have a seek function. So why check ppos?

Thanks,
Hans