Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753378AbbHERN5 (ORCPT ); Wed, 5 Aug 2015 13:13:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47293 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753331AbbHERNz (ORCPT ); Wed, 5 Aug 2015 13:13:55 -0400 Date: Wed, 5 Aug 2015 12:13:49 -0500 From: David Teigland To: Guenter Roeck Cc: linux-watchdog@vger.kernel.org, Wim Van Sebroeck , linux-kernel@vger.kernel.org, Timo Kokkonen , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , linux-doc@vger.kernel.org, Jonathan Corbet Subject: Re: [PATCH 0/8] watchdog: Add support for keepalives triggered by infrastructure Message-ID: <20150805171349.GA15472@redhat.com> References: <1438654414-29259-1-git-send-email-linux@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438654414-29259-1-git-send-email-linux@roeck-us.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2262 Lines: 42 On Mon, Aug 03, 2015 at 07:13:26PM -0700, Guenter Roeck wrote: > - Some watchdogs have a very short maximum timeout, in the range of just a few > seconds. Such low timeouts are difficult if not impossible to support from > user space. Drivers supporting such watchdog hardware need to implement > a timer function to augment heartbeats from user space. > - A new status flag, WDOG_RUNNING, informs the watchdog subsystem that a > watchdog is running, and that the watchdog subsystem needs to generate > heartbeat requests while the associated watchdog device is closed. > Patch #2 adds timer functionality to the watchdog core. It solves the problem > of short maximum hardware timeouts by augmenting heartbeats triggered from > user space with internally triggered heartbeats. > > Patch #3 adds functionality to generate heartbeats while the watchdog device is > closed. It handles situation where where the watchdog is running after > the driver has been instantiated, but the device is not yet opened, > and post-close situations necessary if a watchdog can not be stopped. These sound concerning because it seems that heartbeats could be generated outside of the direct control of userspace. I have a program that depends on having direct control over whether heartbeats are generated (or more specifically, *not* generated.) If these new features introduce a new way for heartbeats to be generated, is there a way I can detect or disable that behavior from userspace? Unwanted heartbeats could break my program and may lead to data corruption. A related issue from some years ago is the unfortunate fact that closing the watchdog device also generates a heartbeat. I'd like to disable that also, and submitted a patch for it here: http://www.spinics.net/lists/linux-watchdog/msg01477.html (Without the patch, I have to work around it by closing the device prematurely as a way to generate the potentially final heartbeat, and then reopen it again if I want to continue the heartbeats.) Dave -- 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/