Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754824AbdCGJKz convert rfc822-to-8bit (ORCPT ); Tue, 7 Mar 2017 04:10:55 -0500 Received: from mx2.suse.de ([195.135.220.15]:47893 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753331AbdCGJKr (ORCPT ); Tue, 7 Mar 2017 04:10:47 -0500 Date: Tue, 7 Mar 2017 10:08:46 +0100 From: Jean Delvare To: Guenter Roeck Cc: Peter =?UTF-8?B?SMO8d2U=?= , linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Question about hwmon_attr_show_string Message-ID: <20170307100846.0487135b@endymion> In-Reply-To: <20170306234755.GA16512@roeck-us.net> References: <201703030133.01363.PeterHuewe@gmx.de> <201703062148.36101.PeterHuewe@gmx.de> <20170306234755.GA16512@roeck-us.net> Organization: SUSE Linux X-Mailer: Claws Mail 3.12.0 (GTK+ 2.24.31; x86_64-suse-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2266 Lines: 61 Hi Guenter, On Mon, 6 Mar 2017 15:47:55 -0800, Guenter Roeck wrote: > On Mon, Mar 06, 2017 at 09:48:35PM +0100, Peter Hüwe wrote: > > Hi Guenter, > > > > I was wondering whether there was a particular reason why > > hwmon_attr_show_string passes only an "empty" pointer(pointer) to the ops- > > >read_string function rather than the buffer itself? > > > > Wouldn't this mean that in ops->read_string I'd have to reserve some space for > > the value on the heap (and taking care to free it somewhere, since returning > > an address on the stack is bad idea), instead of calling sprintf(buf, "%s\n", > > s) directly? > > > > With the current implementation I have to sprintf it into my local buffer and > > you sprintf it again into the final buffer. > > The idea was that the called code would return a pointer to a constant string, > ie one that isn't changing from call to call. In that case, what about the following change? Subject: hwmon: Constify str parameter of hwmon_ops->read_string The read_string callback is supposed to retrieve a pointer to a constant string. Signed-off-by: Jean Delvare --- drivers/hwmon/hwmon.c | 2 +- include/linux/hwmon.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) --- linux-4.10.orig/drivers/hwmon/hwmon.c 2017-02-19 23:34:00.000000000 +0100 +++ linux-4.10/drivers/hwmon/hwmon.c 2017-03-07 08:22:27.784527968 +0100 @@ -186,7 +186,7 @@ static ssize_t hwmon_attr_show_string(st char *buf) { struct hwmon_device_attribute *hattr = to_hwmon_attr(devattr); - char *s; + const char *s; int ret; ret = hattr->ops->read_string(dev, hattr->type, hattr->attr, --- linux-4.10.orig/include/linux/hwmon.h 2017-02-19 23:34:00.000000000 +0100 +++ linux-4.10/include/linux/hwmon.h 2017-03-07 08:21:28.247998585 +0100 @@ -336,7 +336,7 @@ struct hwmon_ops { int (*read)(struct device *dev, enum hwmon_sensor_types type, u32 attr, int channel, long *val); int (*read_string)(struct device *dev, enum hwmon_sensor_types type, - u32 attr, int channel, char **str); + u32 attr, int channel, const char **str); int (*write)(struct device *dev, enum hwmon_sensor_types type, u32 attr, int channel, long val); }; -- Jean Delvare SUSE L3 Support