linux-kernel - Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of running thread

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Message-ID: <974364259.6329.1453930475174.JavaMail.zimbra@efficios.com>
Date:	Wed, 27 Jan 2016 21:34:35 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	linux-api <linux-api@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Watson <davejwatson@...com>, Chris Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...hat.com>, Ben Maurer <bmaurer@...com>,
	rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number
 of running thread

----- On Jan 27, 2016, at 12:37 PM, Thomas Gleixner tglx@...utronix.de wrote:

> On Wed, 27 Jan 2016, Thomas Gleixner wrote:
> 
>> On Wed, 27 Jan 2016, Mathieu Desnoyers wrote:
>> > ----- On Jan 27, 2016, at 12:22 PM, Thomas Gleixner tglx@...utronix.de wrote:
>> > Sounds fair. What is the recommended typing for "ptr" then ?
>> > uint32_t ** or uint32_t * ?
>> > 
>> > It would be expected to pass a "uint32_t *" for the set
>> > operation, but the "get" operation requires a "uint32_t **".
>> 
>> Well, you can't change the types depending on the opcode, so you need to stick
>> with **.
> 
> Alternatively you make it:
> 
>  (opcode, *newptr, **oldptr, flags);

I'm tempted to stick to (opcode, **ptr, flags), because
other syscalls that have "*newptr", "**oldptr"
typically have them because they save the current state
into oldptr, and set the new state, which is really
not the case here. To eliminate any risk of confusion,
I am tempted to keep a single "**ptr".

Unless someone has a better idea...

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com