From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752798AbbFDJhg (ORCPT ); Thu, 4 Jun 2015 05:37:36 -0400 Received: from mail-lb0-f179.google.com ([209.85.217.179]:36230 "EHLO mail-lb0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752044AbbFDJhb (ORCPT ); Thu, 4 Jun 2015 05:37:31 -0400 From: Rasmus Villemoes To: Andrew Morton , Steven Rostedt , Ingo Molnar Cc: Rasmus Villemoes , linux-kernel@vger.kernel.org Subject: [RFC/PATCH 3/8] blktrace: use strreplace in do_blk_trace_setup Date: Thu, 4 Jun 2015 11:37:10 +0200 Message-Id: <1433410636-26812-4-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.1.3 In-Reply-To: <1433410636-26812-1-git-send-email-linux@rasmusvillemoes.dk> References: <1433410636-26812-1-git-send-email-linux@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Part of the disassembly of do_blk_trace_setup: 231b: e8 00 00 00 00 callq 2320 231c: R_X86_64_PC32 strlen+0xfffffffffffffffc 2320: eb 0a jmp 232c 2322: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1) 2328: 48 83 c3 01 add $0x1,%rbx 232c: 48 39 d8 cmp %rbx,%rax 232f: 76 47 jbe 2378 2331: 41 80 3c 1c 2f cmpb $0x2f,(%r12,%rbx,1) 2336: 75 f0 jne 2328 2338: 41 c6 04 1c 5f movb $0x5f,(%r12,%rbx,1) 233d: 4c 89 e7 mov %r12,%rdi 2340: e8 00 00 00 00 callq 2345 2341: R_X86_64_PC32 strlen+0xfffffffffffffffc 2345: eb e1 jmp 2328 Yep, that's right: gcc isn't smart enough to realize that replacing '/' by '_' cannot change the strlen(), so we call it again and again (at least when a '/' is found). Even if gcc were that smart, this construction would still loop over the string twice, once for the initial strlen() call and then the open-coded loop. Let's simply use strreplace() instead. Signed-off-by: Rasmus Villemoes --- kernel/trace/blktrace.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 483cecfa5c17..4eeae4674b5a 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -439,7 +439,7 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, { struct blk_trace *old_bt, *bt = NULL; struct dentry *dir = NULL; - int ret, i; + int ret; if (!buts->buf_size || !buts->buf_nr) return -EINVAL; @@ -451,9 +451,7 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, * some device names have larger paths - convert the slashes * to underscores for this to work as expected */ - for (i = 0; i < strlen(buts->name); i++) - if (buts->name[i] == '/') - buts->name[i] = '_'; + strreplace(buts->name, '/', '_'); bt = kzalloc(sizeof(*bt), GFP_KERNEL); if (!bt) -- 2.1.3