Message-ID: <1413482157.8915.3.camel@perches.com>
Subject: Re: [PATCH 3v] char: hw_random: core.c:  Changed from using strncat
 to strlcat
From: Joe Perches <joe@perches.com>
To: Jason Cooper <jason@lakedaemon.net>
Cc: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>,
        Matt Mackall <mpm@selenic.com>,
        Herbert Xu <herbert@gondor.apana.org.au>, Torsten Duwe <duwe@lst.de>,
        "Theodore Ts'o" <tytso@mit.edu>, Amit Shah <amit.shah@redhat.com>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Kees Cook <keescook@chromium.org>,
        Dan Carpenter <dan.carpenter@oracle.com>, linux-kernel@vger.kernel.org
Date: Thu, 16 Oct 2014 10:55:57 -0700
In-Reply-To: <20141016174823.GM17447@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>
Content-Type: text/plain; charset="ISO-8859-1"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org

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.

--
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/