linux-kernel - Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR

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Date:	Fri, 03 Feb 2012 09:32:54 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>, Valdis.Kletnieks@...edu
Subject: Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7

On 02/03/2012 01:28 AM, Cyrill Gorcunov wrote:
> static __init int kcmp_cookie_init(void)
> {
> 	int i, j;
>
> 	for (i = 0; i<  KCMP_TYPES; i++) {
> 		for (j = 0; j<  2; j++)
> 			get_random_bytes(&cookies[i][j], sizeof(long));
> 		cookies[i][1] |= (~(~0UL>>   1) | 1);
> 	}
>
> 	return 0;
> }
>
> I thought in first place that sizeof(cookies[i][j]) would allow me
> to change type of cookies in one place (ie at declaration) but
> if cookies type will be changed -- the code will need careful review
> anway, so sizeof(long) will be enough I think.
>
> On the other hands, maybe more clean variant will be
>
> static __init int kcmp_cookie_init(void)
> {
> 	const int size = sizeof(cookies[0][0]);
> 	int i, j;
>
> 	for (i = 0; i<  KCMP_TYPES; i++) {
> 		for (j = 0; j<  2; j++)
> 			get_random_bytes(&cookies[i][j], size);
> 		cookies[i][1] |= (~(~0UL>>   1) | 1);
> 	}
>

How about:

	const int size = sizeof(cookies[0]);

	get_random_bytes(&cookies[i], size);

... and skip the completely unnecessary for loop?

	-hpa

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