From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail06.adl2.internode.on.net ([150.101.137.129]:15139 "EHLO ipmail06.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750797AbcCBWrd (ORCPT ); Wed, 2 Mar 2016 17:47:33 -0500 Date: Thu, 3 Mar 2016 09:47:30 +1100 From: Dave Chinner To: Al Viro Cc: Frank Sorenson , linux-fsdevel@vger.kernel.org, dwysocha@redhat.com, lvaz@redhat.com Subject: Re: [PATCH 0/5] Add trace events for filesystem freeze/thaw events Message-ID: <20160302224730.GP29057@dastard> References: <1456945319-16283-1-git-send-email-sorenson@redhat.com> <20160302214744.GN17997@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160302214744.GN17997@ZenIV.linux.org.uk> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Mar 02, 2016 at 09:47:44PM +0000, Al Viro wrote: > On Wed, Mar 02, 2016 at 01:01:54PM -0600, Frank Sorenson wrote: > Let's provide a sane stable ABI for the things it's going to be > used for. Because _this_ is very likely to end up with > "something needs to keep track of those events boot-to-shutdown" -> > "something in systemd guts will be keeping track of those and > broadcasting the collected information on state over dbus for the > rest of dbus-infested system to see" -> "touch any details and you > break real userland code" -> "it's cast in stone forever". With > systemd folks not particularly happy about the details, but even > less happy about the need to make the already grotty code parsing > those depend on the kernel version. > > And as much as I don't like Lennart et.al., in this case they would > be perfectly justified. Information in question is potentially interesting, > due to the form it is presented in one really needs to keep track of all > messages since boot to make any use of it and it's clearly a job for > a long-running daemon to collect those - nothing else would be able to. > And once such a daemon starts using that, its authors would have very good > reasons to demand the fucking ABI to be fucking stable. After all, they > weren't the ones who came up with the nasty details we might want to change. > > So let's get it right. Preferably - without need for boot-to-shutdown > tracking just to mirror the state. What do we really want? > > * an ioctl to query the state (frozen/freezing/not frozen) for something in > util-linux to use? > > * /proc/fs/freezing and /proc/fs/frozen, with ->s_id of affected filesystems > or, pehaps, one file with (frozen|freezing) + ->s_id? > > * ability to audit on state changes? That'd need some thought re what to > do when some joker freezes the fs syslogd is logging to... > > * something else entirely? Such as: https://lkml.org/lkml/2015/6/16/456 Cheers, Dave. -- Dave Chinner david@fromorbit.com