Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752232AbaJPRmS (ORCPT ); Thu, 16 Oct 2014 13:42:18 -0400 Received: from mail-la0-f52.google.com ([209.85.215.52]:43998 "EHLO mail-la0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751935AbaJPRmR (ORCPT ); Thu, 16 Oct 2014 13:42:17 -0400 MIME-Version: 1.0 In-Reply-To: <1413480303.6702.7.camel@perches.com> References: <1413479722-29247-1-git-send-email-rickard_strandqvist@spectrumdigital.se> <1413480303.6702.7.camel@perches.com> From: Rickard Strandqvist Date: Thu, 16 Oct 2014 19:41:55 +0200 Message-ID: Subject: Re: [PATCH 3v] char: hw_random: core.c: Changed from using strncat to strlcat To: Joe Perches Cc: Matt Mackall , Herbert Xu , Torsten Duwe , "Theodore Ts'o" , Jason Cooper , 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 19:25 GMT+02:00 Joe Perches : > 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? > > You could use a temporary for the returned length > of the strlcat so that if it's shorter than > the buffer, the next strlcat can start at the > appropriate known position instead of having > to do the initial strlen again and again. > Hi Joe Yes that did not take advantage last strlcat was foolish. But the others, I am very hesitant about. Because strlcat like snprintf and strlcpy returns the length that would be copied rather than what is actually copied. Hence such a code to be even more complex than before. 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/