[PATCH 3/8] ppc64: add a watchdog driver for rtas

[Nathan Lynch]

Arnd Bergmann wrote:
> On Dinsdag 17 Mai 2005 22:40, Nathan Lynch wrote:
> > Arnd Bergmann wrote:
> > > +static volatile int wdrtas_miscdev_open = 0;
> > ...
> > > +static int
> > > +wdrtas_open(struct inode *inode, struct file *file)
> > > +{
> > > +	/* only open once */
> > > +	if (xchg(&wdrtas_miscdev_open,1))
> > > +		return -EBUSY;
> > 
> > The volatile and xchg strike me as an obscure method for ensuring only
> > one process at a time can open this file.  Any reason a semaphore
> > couldn't be used?
> 
> A semaphore would also be the wrong approach since we don't want
> processes to block but instead to fail opening the watchdog twice.

I should have been more explicit.  What I had in mind was using
down_trylock and returning -EBUSY if it failed.

Nathan