From patchwork Sat Dec 22 16:20:08 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 10741327 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 823B6161F for ; Sat, 22 Dec 2018 16:47:28 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 721C3289F5 for ; Sat, 22 Dec 2018 16:47:28 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 66E1928A12; Sat, 22 Dec 2018 16:47:28 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E00F8289F5 for ; Sat, 22 Dec 2018 16:47:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725899AbeLVQr1 (ORCPT ); Sat, 22 Dec 2018 11:47:27 -0500 Received: from mail.kernel.org ([198.145.29.99]:36912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725268AbeLVQrO (ORCPT ); Sat, 22 Dec 2018 11:47:14 -0500 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9000F21B8C; Sat, 22 Dec 2018 16:28:57 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.91) (envelope-from ) id 1gak92-0001Ea-KA; Sat, 22 Dec 2018 11:28:56 -0500 Message-Id: <20181222162856.518489380@goodmis.org> User-Agent: quilt/0.65 Date: Sat, 22 Dec 2018 11:20:08 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Joe Perches , Namhyung Kim , Linus Torvalds , Yoshinori Sato , Rich Felker , linux-sh@vger.kernel.org, Tom Zanussi , Greg Kroah-Hartman Subject: [for-next][PATCH 1/5] string.h: Add str_has_prefix() helper function References: <20181222162007.697862256@goodmis.org> MIME-Version: 1.0 Sender: linux-sh-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: "Steven Rostedt (VMware)" A discussion came up in the trace triggers thread about converting a bunch of: strncmp(str, "const", sizeof("const") - 1) use cases into a helper macro. It started with: strncmp(str, const, sizeof(const) - 1) But then Joe Perches mentioned that if a const is not used, the sizeof() will be the size of a pointer, which can be bad. And that gcc will optimize strlen("const") into "sizeof("const") - 1". Thinking about this more, a quick grep in the kernel tree found several (thousands!) of cases that use this construct. A quick grep also revealed that there's probably several bugs in that use case. Some are that people forgot the "- 1" (which I found) and others could be that the constant for the sizeof is different than the constant (although, I haven't found any of those, but I also didn't look hard). I figured the best thing to do is to create a helper macro and place it into include/linux/string.h. And go around and fix all the open coded versions of it later. Note, gcc appears to optimize this when we make it into an always_inline static function, which removes a lot of issues that a macro produces. Link: http://lkml.kernel.org/r/e3e754f2bd18e56eaa8baf79bee619316ebf4cfc.1545161087.git.tom.zanussi@linux.intel.com Link: http://lkml.kernel.org/r/20181219211615.2298e781@gandalf.local.home Link: http://lkml.kernel.org/r/CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com Cc: Tom Zanussi Cc: Greg Kroah-Hartman Suggestions-by: Linus Torvalds Suggestions-by: Joe Perches Suggestions-by: Andreas Schwab Signed-off-by: Steven Rostedt (VMware) --- include/linux/string.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/include/linux/string.h b/include/linux/string.h index 27d0482e5e05..7927b875f80c 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -456,4 +456,24 @@ static inline void memcpy_and_pad(void *dest, size_t dest_len, memcpy(dest, src, dest_len); } +/** + * str_has_prefix - Test if a string has a given prefix + * @str: The string to test + * @prefix: The string to see if @str starts with + * + * A common way to test a prefix of a string is to do: + * strncmp(str, prefix, sizeof(prefix) - 1) + * + * But this can lead to bugs due to typos, or if prefix is a pointer + * and not a constant. Instead use str_has_prefix(). + * + * Returns: 0 if @str does not start with @prefix + strlen(@prefix) if @str does start with @prefix + */ +static __always_inline size_t str_has_prefix(const char *str, const char *prefix) +{ + size_t len = strlen(prefix); + return strncmp(str, prefix, len) == 0 ? len : 0; +} + #endif /* _LINUX_STRING_H_ */