From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Lehmann Subject: Re: f2fs bug: Unable to mount big volumes in kernel 4.5 Date: Wed, 23 Mar 2016 22:00:10 +0100 Message-ID: <20160323205204.GB4443@schmorp.de> References: <56EEC766.2030503@davizone.at> <20160320224654.GB4752@jaegeuk.hsd1.ca.comcast.net> <00d401d18320$75f94e80$61ebeb80$@samsung.com> <56F06067.2060404@davizone.at> <56F07C02.2020106@matthiasprager.de> <20160322203613.GA14498@jaegeuk.gateway> <56F29214.9040001@davizone.at> <56F2C755.5060402@matthiasprager.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-1.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1aipt9-00055N-7i for linux-f2fs-devel@lists.sourceforge.net; Wed, 23 Mar 2016 21:00:23 +0000 Received: from mail.nethype.de ([5.9.56.24]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:AES128-SHA:128) (Exim 4.76) id 1aipt7-0003SV-F0 for linux-f2fs-devel@lists.sourceforge.net; Wed, 23 Mar 2016 21:00:23 +0000 Content-Disposition: inline In-Reply-To: <56F2C755.5060402@matthiasprager.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net To: Matthias Prager Cc: Jaegeuk Kim , David Gnedt , linux-f2fs-devel@lists.sourceforge.net On Wed, Mar 23, 2016 at 05:41:57PM +0100, Matthias Prager wrote: > detail. Writing on a read-only fs is a no go! There usually is a reason > why someone mounts an filesystem read-only and f2fs should not simply > ignore such a flag. Hmm, no. Even an unusual case is enough, such as mounting it read-only for data recovery because the underlying device dies on writes (quite likely for ssds, the primary target for f2fs). However, other linux filesystems either replay their journal on readonly mounts, or even *require* a replay (most have a flag to prevent that, but that might not help data recovery). In fact, my example above can relatively easily worked around using device mapper and a temporary snapshot volume for writes. So, the "ro" mount flag in linux does not mean "do not write to the backing store", and did not have that meaning for a long time, so it's fine for f2fs to write even for ro mounts. That means the correct behaviour for f2fs is to write unless "norecovery" has been specified, which already exists for this purpose on f2fs. Different behaviour would put f2fs at odds with other existing filesystems, which write on "ro" mounts to gain integrity. Even better would be if there was a "force" or similar option which would allow me to mount filesystems with possibly bad superblock data. This could even be rolled into the existing "norecovery" switch, which, when given, could try to mount even if the superblock has (some amount of) bad data. -- The choice of a Deliantra, the free code+content MORPG -----==- _GNU_ http://www.deliantra.net ----==-- _ generation ---==---(_)__ __ ____ __ Marc Lehmann --==---/ / _ \/ // /\ \/ / schmorp@schmorp.de -=====/_/_//_/\_,_/ /_/\_\ ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785351&iu=/4140