From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967319AbcA1LND (ORCPT ); Thu, 28 Jan 2016 06:13:03 -0500 Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:34690 "EHLO e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964950AbcA1LM6 (ORCPT ); Thu, 28 Jan 2016 06:12:58 -0500 X-IBM-Helo: d06dlp03.portsmouth.uk.ibm.com X-IBM-MailFrom: heiko.carstens@de.ibm.com X-IBM-RcptTo: linux-api@vger.kernel.org;linux-kernel@vger.kernel.org Date: Thu, 28 Jan 2016 12:12:38 +0100 From: Heiko Carstens To: Mathieu Desnoyers Cc: Josh Triplett , Thomas Gleixner , Paul Turner , Andrew Hunter , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-api , Andy Lutomirski , Andi Kleen , Dave Watson , Chris Lameter , Ingo Molnar , Ben Maurer , rostedt , "Paul E. McKenney" , Linus Torvalds , Andrew Morton , Russell King , Catalin Marinas , Will Deacon , Michael Kerrisk Subject: Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of running thread Message-ID: <20160128111238.GA5418@osiris> References: <1453913683-28915-1-git-send-email-mathieu.desnoyers@efficios.com> <1453913683-28915-2-git-send-email-mathieu.desnoyers@efficios.com> <671969438.6129.1453915918933.JavaMail.zimbra@efficios.com> <974364259.6329.1453930475174.JavaMail.zimbra@efficios.com> <20160127221142.GA8935@cloud> <75735238.6347.1453934857246.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <75735238.6347.1453934857246.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16012811-0009-0000-0000-0000076F6FDF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 27, 2016 at 10:47:37PM +0000, Mathieu Desnoyers wrote: > ----- On Jan 27, 2016, at 5:11 PM, Josh Triplett josh@joshtriplett.org wrote: > > > On Wed, Jan 27, 2016 at 09:34:35PM +0000, Mathieu Desnoyers wrote: > >> ----- On Jan 27, 2016, at 12:37 PM, Thomas Gleixner tglx@linutronix.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@linutronix.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... > > > > Either that or you could define it as "void *" and interpret it based on > > flags, but that seems unfortunate; let's not imitate ioctl-style > > typeless parameters. I'd stick with the double pointer and the current > > behavior. > > Allright, will do! Thanks for the feedback :) Please don't forget that you also need to implement compat handling since the size of the pointer that is being pointed to is only four bytes for compat tasks.