From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [to-be-updated] kernelh-add-build_bug_on_not_power_of_2.patch removed from -mm tree Date: Fri, 08 Jan 2010 13:11:53 -0800 Message-ID: <201001082111.o08LBrSq014250@imap1.linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:41542 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753828Ab0AHVMO (ORCPT ); Fri, 8 Jan 2010 16:12:14 -0500 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: rdreier@cisco.com, rolandd@cisco.com, mm-commits@vger.kernel.org The patch titled kernel.h: add BUILD_BUG_ON_NOT_POWER_OF_2() has been removed from the -mm tree. Its filename was kernelh-add-build_bug_on_not_power_of_2.patch This patch was dropped because an updated version will be merged The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: kernel.h: add BUILD_BUG_ON_NOT_POWER_OF_2() From: Roland Dreier When code relies on a constant being a power of 2: #define FOO 512 /* must be a power of 2 */ it would be nice to be able to do: BUILD_BUG_ON(!is_power_of_2(FOO)); However applying an inline function does not result in a compile-time constant that can be used with BUILD_BUG_ON(), so trying that gives results in: error: bit-field '' width not an integer constant As suggested by akpm, rather than monkeying around with is_power_of_2() and risking gcc warts about constant expressions, just create a macro BUILD_BUG_ON_NOT_POWER_OF_2() to encapsulate this common requirement. Signed-off-by: Roland Dreier Signed-off-by: Andrew Morton --- include/linux/kernel.h | 4 ++++ 1 file changed, 4 insertions(+) diff -puN include/linux/kernel.h~kernelh-add-build_bug_on_not_power_of_2 include/linux/kernel.h --- a/include/linux/kernel.h~kernelh-add-build_bug_on_not_power_of_2 +++ a/include/linux/kernel.h @@ -703,6 +703,10 @@ static inline void ftrace_dump(void) { } struct sysinfo; extern int do_sysinfo(struct sysinfo *info); +/* Force a compilation error if expression is not a power of 2 */ +#define BUILD_BUG_ON_NOT_POWER_OF_2(n) \ + BUILD_BUG_ON(((n) != 0 && (((n) & ((n) - 1)) == 0))) + /* Force a compilation error if condition is true, but also produce a result (of value 0 and type size_t), so the expression can be used e.g. in a structure initializer (or where-ever else comma expressions _ Patches currently in -mm which might be from rdreier@cisco.com are kfifo-use-void-pointers-for-user-buffers.patch kfifo-sanitize-_user-error-handling.patch kfifo-add-kfifo_out_peek.patch kfifo-add-kfifo_initialized.patch kfifo-document-everywhere-that-size-has-to-be-power-of-two.patch kernelh-add-build_bug_on_not_power_of_2.patch ecryptfs-another-lockdep-issue.patch