linux-kernel - Re: [PATCH linux-next v3 1/2] irq: Add CPU mask affinity hint

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Date:	Fri, 30 Apr 2010 23:17:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ben Hutchings <bhutchings@...arflare.com>
cc:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	davem@...emloft.net, arjan@...ux.jf.intel.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH linux-next v3 1/2] irq: Add CPU mask affinity hint

On Fri, 30 Apr 2010, Ben Hutchings wrote:
> On Fri, 2010-04-30 at 13:23 -0700, Peter P Waskiewicz Jr wrote:
> > +int irq_register_affinity_hint(unsigned int irq, const struct cpumask *m)
> > +{
> > +	struct irq_desc *desc = irq_to_desc(irq);
> > +	unsigned long flags;
> > +
> > +	if (!desc)
> > +		return -EINVAL;
> 
> Is it possible for irq_to_desc(irq) to be NULL?  This function already
> assumes that the caller 'owns' the IRQ.

Oh come on. Driver writers get everything wrong and not checking on an
invalid irq number is better than crashing :)

> > +static int irq_affinity_hint_proc_show(struct seq_file *m, void *v)
> > +{
> > +	struct irq_desc *desc = irq_to_desc((long)m->private);
> > +	unsigned long flags;
> > +	cpumask_var_t mask;
> > +	int ret = -EINVAL;
> 
> I don't think this should be returning -EINVAL if the affinity hint is
> missing.  That means 'invalid argument', but there is nothing invalid
> about trying to read() the corresponding file.  The file should simply
> be empty if there is no hint.  (Actually it might be better if it didn't
> appear at all, but that would be a pain to implement.)

I agree that -EINVAL is not really a good match.

How about just returning CPU_MASK_ALL if desc->affinity_hint is not
set ?

Thanks,

	tglx
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