From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751960AbbIOV5J (ORCPT ); Tue, 15 Sep 2015 17:57:09 -0400 Received: from mail-pa0-f54.google.com ([209.85.220.54]:35232 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751772AbbIOV5H (ORCPT ); Tue, 15 Sep 2015 17:57:07 -0400 Subject: Re: First kernel patch (optimization) To: Eric Curtin References: <1442346759-3740-1-git-send-email-ericcurtin17@gmail.com> Cc: linux-kernel@vger.kernel.org From: Alexander Duyck Message-ID: <55F89431.4070605@gmail.com> Date: Tue, 15 Sep 2015 14:57:05 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <1442346759-3740-1-git-send-email-ericcurtin17@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/15/2015 12:52 PM, Eric Curtin wrote: > My first kernel patch, hope I did everything correctly! Instead of calling strlen on every iteration of the for loop, just call it once instead and store in a variable. > > Signed-off-by: Eric Curtin > > diff --git a/tools/usb/usbip/src/usbip_detach.c b/tools/usb/usbip/src/usbip_detach.c > index 05c6d15..9db9d21 100644 > --- a/tools/usb/usbip/src/usbip_detach.c > +++ b/tools/usb/usbip/src/usbip_detach.c > @@ -47,7 +47,9 @@ static int detach_port(char *port) > uint8_t portnum; > char path[PATH_MAX+1]; > > - for (unsigned int i = 0; i < strlen(port); i++) > + unsigned int port_len = strlen(port); > + > + for (unsigned int i = 0; i < port_len; i++) > if (!isdigit(port[i])) { > err("invalid port %s", port); > return -1; > You should probably run this through scripts/checkpatch.pl as I don't think declaring i inside the loop is consistent with the kernel coding standard. Also you don't want the space between port_len and the declaration of path. Also you might want to consider just running the loop from port_len down to 0 doing something like: while (port_len) { if (!isdigit(port[--port_len])) { err("invalid port %s", port); return -1; The advantage to running the loop backwards is that you have to carry one less variable which means one less register to mess with in the final compiled code. - Alex