From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:40648 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932185AbbJ1Mg2 (ORCPT ); Wed, 28 Oct 2015 08:36:28 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1ZrPxp-0003aA-N0 for linux-btrfs@vger.kernel.org; Wed, 28 Oct 2015 13:36:25 +0100 Received: from ip98-167-165-199.ph.ph.cox.net ([98.167.165.199]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 28 Oct 2015 13:36:25 +0100 Received: from 1i5t5.duncan by ip98-167-165-199.ph.ph.cox.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 28 Oct 2015 13:36:25 +0100 To: linux-btrfs@vger.kernel.org From: Duncan <1i5t5.duncan@cox.net> Subject: Re: Questions about FIEMAP Date: Wed, 28 Oct 2015 12:36:11 +0000 (UTC) Message-ID: References: <561BB531.6070706@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Wang, Zhiye posted on Wed, 28 Oct 2015 09:57:29 +0000 as excerpted: > Thank you all for your comments. > > A further question is: if I mount a btrfs file system in "readonly" > mode, will any operation cause the blocks of a file get changed? Note that both bind-mounts and btrfs subvolume mounts can be used to make parts of a filesystem appear in multiple locations in the filesystem tree. Because these different mounts can be separately mounted read-only or writable, there's no guarantee that just because a filesystem or part of it is read-only mounted in one location, it's read-only mounted everywhere it can be accessed, and thus no guarantee that files even on a read-only mounted filesystem or subvolume won't actually change out from under you. However, bind-mounts in particular aren't btrfs specific, so just because btrfs subvolumes add another case in which the above can be true, doesn't mean bind-mounts can't be used on other filesystems to effect the same sort of otherwise read-only file instabilities. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman