linux-kernel - Re: cpumask: fix compat getaffinity

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Message-Id: <201012151540.51975.arnd@arndb.de>
Date:	Wed, 15 Dec 2010 15:40:51 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Josh Hunt <joshhunt00@...il.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Milton Miller <miltonm@....com>, Greg KH <greg@...ah.com>,
	linux-kernel@...r.kernel.org, anton@...ba.org
Subject: Re: cpumask: fix compat getaffinity

On Tuesday 14 December 2010, Josh Hunt wrote:
> 
> I realize this thread is fairly old, but I have a question about this
> statement in the changelog:
> 
> > On NUMA systems with less than 32 possibly CPUs, the
> > current compat_sys_sched_getaffinity now returns '4'
> > instead of the actual NR_CPUS/8, which makes libnuma
> > bail out when parsing the cpumap.
> 
> This does not seem accurate, at least not on my system with NR_CPUS=32
> and nr_cpu_ids=8. The smallest value retlen will ever be set to is
> sizeof(long) which is 8 on most modern systems. This breaks the
> statement that this function will now return NR_CPUS/8.

Yes, I think the description is a bit misleading there.
The point was that it should return the number that the
sysfs files are based on, instead of the smallest multiple
of sizeof(compat_long) that can hold the installed CPUs.

	Arnd
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