Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752863AbaJPSMJ (ORCPT ); Thu, 16 Oct 2014 14:12:09 -0400 Received: from mail-lb0-f175.google.com ([209.85.217.175]:44571 "EHLO mail-lb0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751636AbaJPSMH (ORCPT ); Thu, 16 Oct 2014 14:12:07 -0400 MIME-Version: 1.0 In-Reply-To: <20141016180517.GO17447@titan.lakedaemon.net> References: <1413479722-29247-1-git-send-email-rickard_strandqvist@spectrumdigital.se> <1413480303.6702.7.camel@perches.com> <20141016174823.GM17447@titan.lakedaemon.net> <1413482157.8915.3.camel@perches.com> <20141016180517.GO17447@titan.lakedaemon.net> From: Rickard Strandqvist Date: Thu, 16 Oct 2014 20:11:45 +0200 Message-ID: Subject: Re: [PATCH 3v] char: hw_random: core.c: Changed from using strncat to strlcat To: Jason Cooper Cc: Joe Perches , Matt Mackall , Herbert Xu , Torsten Duwe , "Theodore Ts'o" , Amit Shah , Stephen Boyd , Paul Gortmaker , Kees Cook , Dan Carpenter , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-10-16 20:05 GMT+02:00 Jason Cooper : > On Thu, Oct 16, 2014 at 10:55:57AM -0700, Joe Perches wrote: >> On Thu, 2014-10-16 at 13:48 -0400, Jason Cooper wrote: >> > On Thu, Oct 16, 2014 at 10:25:03AM -0700, Joe Perches wrote: >> > > On Thu, 2014-10-16 at 19:15 +0200, Rickard Strandqvist wrote: >> > > > The buf is used to hold the list of hwrng devices registered. >> > > > The old code ensures we don't walk off the end of buf as we >> > > > fill it, but it's unnecessarily complicated and thus difficult >> > > > to maintain. Simplify it by using strlcat. >> > > > We also ensure the string within buf is NULL terminated >> > > > so the final strlen is ok. >> > > [] >> > > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c >> > > [] >> > > > @@ -289,16 +288,13 @@ static ssize_t hwrng_attr_available_show(struct device *dev, >> > > > return -ERESTARTSYS; >> > > > buf[0] = '\0'; >> > > > list_for_each_entry(rng, &rng_list, list) { >> > > > - strncat(buf, rng->name, PAGE_SIZE - ret - 1); >> > > > - ret += strlen(rng->name); >> > > > - strncat(buf, " ", PAGE_SIZE - ret - 1); >> > > > - ret++; >> > > > + strlcat(buf, rng->name, PAGE_SIZE); >> > > > + strlcat(buf, " ", PAGE_SIZE); >> > > > } >> > > > - strncat(buf, "\n", PAGE_SIZE - ret - 1); >> > > > - ret++; >> > > > + strlcat(buf, "\n", PAGE_SIZE); >> > > > mutex_unlock(&rng_mutex); >> > > > >> > > > - return ret; >> > > > + return strlen(buf); >> > > > } >> > > > >> > > > static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR, >> > > >> > > Rickard, can you please use some optimizations here >> > > (and elsewhere) so that strlcat doesn't always have >> > > to strlen the first string and the return doesn't >> > > have to do the strlen too? >> > >> > Joe, is further optimization worth the effort? This function is only >> > called when the end user reads the sysfs file rng_available... >> >> It's unlikely that it matters much here. >> >> I just don't like the repeated and unnecessary strlen. >> >> I do imagine this pattern being repeated though where >> it does matter. > > Agreed. Back to why I like to see descriptions from the author > demonstrating they grok the code they are changing :) > Hi I will submit a new patch without return strlen. All these features are more or less stupid really. You can also read what Linus thinks about this here. https://plus.google.com/111049168280159033135/posts/1amLbuhWbh5 I keep on trying to get a patch that solves one of these stupid functions, but the strncpy in that case. Kind regards Rickard Strandqvist -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/