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

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Date:	Sat, 24 May 2008 00:43:59 +0200
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Leon Woestenberg <leon.woestenberg@...il.com>
Cc:	"Hans J. Koch" <hjk@...utronix.de>,
	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>,
	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Jan Altenberg <jan.altenberg@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Magnus Damm <magnus.damm@...il.com>
Subject: Re: [PATCH 1/1] UIO: Add a write() function to enable/disable
	interrupts

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@...utronix.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

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