From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754438AbbKXNvo (ORCPT ); Tue, 24 Nov 2015 08:51:44 -0500 Received: from mail-lf0-f46.google.com ([209.85.215.46]:36744 "EHLO mail-lf0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752920AbbKXNvh (ORCPT ); Tue, 24 Nov 2015 08:51:37 -0500 From: Rasmus Villemoes To: Joshua Kinard , Alessandro Zummo , Alexandre Belloni Cc: Rasmus Villemoes , rtc-linux@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH 2/2] drivers/rtc/rtc-ds1685.c: don't try to micromanage sysfs output size Date: Tue, 24 Nov 2015 14:51:24 +0100 Message-Id: <1448373085-6353-2-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.6.1 In-Reply-To: <1448373085-6353-1-git-send-email-linux@rasmusvillemoes.dk> References: <1448373085-6353-1-git-send-email-linux@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ...and don't do it wrong. "not ok or N/A" has length 13. Add the trailing newline, and the snprintf return value will be 14. However, we lied to snprintf and told it that only 13 bytes were available. Hence snprintf has only written "not ok or N/" and a trailing '\0' to the buffer. Next we continue lying, this time to the upper sysfs layer, claiming that we wrote 14 meaningful bytes to the buffer. That'll make the upper layer copy "not ok or N/" plus two nul bytes to user space (one nul byte from snprintf, the other since sysfs takes care to clear the buffer before giving it to the ->show method). In the other cases, the claimed buffer size is closer to sufficient, but we'll still get a nul byte instead of a newline written to user space. There's absolutely no reason to try to predict the output size, and there's plenty of room in the buffer, so just use sprintf. Signed-off-by: Rasmus Villemoes --- drivers/rtc/rtc-ds1685.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/drivers/rtc/rtc-ds1685.c b/drivers/rtc/rtc-ds1685.c index 5038122aa8de..535050fc5e9f 100644 --- a/drivers/rtc/rtc-ds1685.c +++ b/drivers/rtc/rtc-ds1685.c @@ -1114,7 +1114,7 @@ ds1685_rtc_sysfs_battery_show(struct device *dev, ctrld = rtc->read(rtc, RTC_CTRL_D); - return snprintf(buf, 13, "%s\n", + return sprintf(buf, "%s\n", (ctrld & RTC_CTRL_D_VRT) ? "ok" : "not ok or N/A"); } static DEVICE_ATTR(battery, S_IRUGO, ds1685_rtc_sysfs_battery_show, NULL); @@ -1137,7 +1137,7 @@ ds1685_rtc_sysfs_auxbatt_show(struct device *dev, ctrl4a = rtc->read(rtc, RTC_EXT_CTRL_4A); ds1685_rtc_switch_to_bank0(rtc); - return snprintf(buf, 13, "%s\n", + return sprintf(buf, "%s\n", (ctrl4a & RTC_CTRL_4A_VRT2) ? "ok" : "not ok or N/A"); } static DEVICE_ATTR(auxbatt, S_IRUGO, ds1685_rtc_sysfs_auxbatt_show, NULL); @@ -1160,9 +1160,7 @@ ds1685_rtc_sysfs_serial_show(struct device *dev, ds1685_rtc_get_ssn(rtc, ssn); ds1685_rtc_switch_to_bank0(rtc); - return snprintf(buf, 24, "%8phC\n", ssn); - - return 0; + return sprintf(buf, "%8phC\n", ssn); } static DEVICE_ATTR(serial, S_IRUGO, ds1685_rtc_sysfs_serial_show, NULL); @@ -1285,7 +1283,7 @@ ds1685_rtc_sysfs_ctrl_regs_show(struct device *dev, tmp = rtc->read(rtc, reg_info->reg) & reg_info->bit; ds1685_rtc_switch_to_bank0(rtc); - return snprintf(buf, 2, "%d\n", (tmp ? 1 : 0)); + return sprintf(buf, "%d\n", (tmp ? 1 : 0)); } /** @@ -1621,7 +1619,7 @@ ds1685_rtc_sysfs_time_regs_show(struct device *dev, tmp = ds1685_rtc_bcd2bin(rtc, tmp, bcd_reg_info->mask, bin_reg_info->mask); - return snprintf(buf, 4, "%d\n", tmp); + return sprintf(buf, "%d\n", tmp); } /** -- 2.6.1