From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:31473 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751194AbaDQP4a (ORCPT ); Thu, 17 Apr 2014 11:56:30 -0400 Message-ID: <534FF9B5.4010207@fb.com> Date: Thu, 17 Apr 2014 11:56:37 -0400 From: Chris Mason MIME-Version: 1.0 To: "Oliver O." , Subject: Re: File changing in snapshot References: <534FF5C1.8070404@gmail.com> In-Reply-To: <534FF5C1.8070404@gmail.com> Content-Type: text/plain; charset="ISO-8859-15"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 04/17/2014 11:39 AM, Oliver O. wrote: > I seem to have observed a file on a (writable) snapshot changing > although there were no writes occuring on the snapshot itself. This is > not supposed to happen, right? > > Sequence of events: > > 1. A (writable) snapshot @home-2014-04-16 is taken on a @home subvolume > mounted at /home. > > 2. The current subvolume (@home) is used (via /home) for continued write > access, no writes are supposed to occur on the snapshot. > > 3. The snapshot @home-2014-04-16 is backed up (using rdiff-backup) to a > different disk. > > 4. As the backup is compared to the snapshot @home-2014-04-16, one file > differs. > > Further analysis: > > The file in @home-2014-04-16 changed its contents (but not mtime or > other metadata) after being backup up from that snapshot. 5 bytes differ. > > The previous snapshot @home-2014-04-10 contains the file in its original > form, which is identical to the backup just taken from @home-2014-04-16. > > The file change appears identically > - on the last snapshot @home-2014-04-16 and > - on the current subvolume used for writing (@home). > > btrfs scrub reports 0 errors. > > At the time the snapshot @home-2014-04-16 was taken, the file (an Excel > file) was probably accessed through Samba, which supposedly uses kernel > oplocks (if that makes a difference). > > Versions: > - Kernel 3.11.0-19-generic (Ubuntu 13.10) > - btrfs-tools 0.19+20130705-1 > - Samba 3.6.18 Was this a nodatacow file? -chris