From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:59358 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753520AbbLGR3Y (ORCPT ); Mon, 7 Dec 2015 12:29:24 -0500 Subject: Re: [PATCH] btrfs: Introduce new mount option to disable tree log replay To: Chandan Rajendra References: <1449468402-27914-1-git-send-email-quwenruo@cn.fujitsu.com> <5665B359.2050906@redhat.com> <2856934.1tulUexfpA@localhost.localdomain> Cc: Qu Wenruo , linux-btrfs@vger.kernel.org From: Eric Sandeen Message-ID: <5665C1F2.8020407@redhat.com> Date: Mon, 7 Dec 2015 11:29:22 -0600 MIME-Version: 1.0 In-Reply-To: <2856934.1tulUexfpA@localhost.localdomain> Content-Type: text/plain; charset=windows-1252 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 12/7/15 10:52 AM, Chandan Rajendra wrote: > On Monday 07 Dec 2015 10:27:05 Eric Sandeen wrote: >> On 12/7/15 12:06 AM, Qu Wenruo wrote: >>> Introduce a new mount option "nologreplay" to co-operate with "ro" mount >>> option to get real readonly mount, like "norecovery" in ext* and xfs. >>> >>> Since the new parse_options() need to check new flags at remount time, >>> so add a new parameter for parse_options(). >>> >>> Signed-off-by: Qu Wenruo >>> --- >>> >>> Documentation/filesystems/btrfs.txt | 5 +++++ >>> fs/btrfs/ctree.h | 4 +++- >>> fs/btrfs/disk-io.c | 7 ++++--- >>> fs/btrfs/super.c | 20 +++++++++++++++++--- >>> 4 files changed, 29 insertions(+), 7 deletions(-) >>> >>> diff --git a/Documentation/filesystems/btrfs.txt >>> b/Documentation/filesystems/btrfs.txt index c772b47..ac4ed68 100644 >>> --- a/Documentation/filesystems/btrfs.txt >>> +++ b/Documentation/filesystems/btrfs.txt >>> @@ -168,6 +168,11 @@ Options with (*) are default options and will not >>> show in the mount options.> >>> notreelog >>> >>> Enable/disable the tree logging used for fsync and O_SYNC writes. >>> >>> + nologreplay >>> + Disable the log tree replay at mount time for real read-only mount. >>> + Must be use with "ro" mount option and can't be disabled by mount >>> + option. >> >> This documentation is not clear to me - "can't be disabled by mount option?" >> >> I think you mean to talk about remount here? Perhaps something like: >> >> "... Must be used with 'ro' mount option. A filesystem mounted with the >> 'nologreplay' option cannot transition to a read-write mount via >> remount,rw - the filesystem must be unmounted and remounted if read-write >> access is desired." >> > Eric, I had assumed the same logic with respect to the transition from 'ro' to > 'rw' via remount. But when doing so, btrfs_remount() flags an error only when > a valid 'tree log' tree is present in the filesystem > i.e. btrfs_super_block->log_root has a non-zero value. Otherwise, > btrfs_remount() does not seem to have any problem with the transition from > 'ro' to 'rw'. Ok, I don't know if that's intended - but I think the docs should be clarified to explicitly state the expected behavior in any case. FWIW, new mount options and their descriptions should be added to BTRFS-MOUNT(5) as well. -Eric