From: Eric Sandeen Subject: [PATCH] ext3: allow specifying external journal by pathname mount option Date: Tue, 30 Jul 2013 17:26:24 -0500 Message-ID: <51F83D90.5080708@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Leonardo Menezes Vaz To: ext4 development , Jan Kara Return-path: Received: from mx1.redhat.com ([209.132.183.28]:15142 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754588Ab3G3W0b (ORCPT ); Tue, 30 Jul 2013 18:26:31 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: It's always been a hassle that if an external journal's device number changes, the filesystem won't mount. And since boot-time enumeration can change, device number changes aren't unusual. The current mechanism to update the journal location is by passing in a mount option w/ a new devnum, but that's a hassle; it's a manual approach, fixing things after the fact. Adding a mount option, "-o journal_path=/dev/$DEVICE" would help, since then we can do i.e. # mount -o journal_path=/dev/disk/by-label/$JOURNAL_LABEL /mnt and it'll mount even if the devnum has changed, as shown here: # losetup /dev/loop0 journalfile # mke2fs -L mylabel-journal -O journal_dev /dev/loop0 # mkfs.ext3 -L mylabel -J device=/dev/loop0 /dev/sdb1 Change the journal device number: # losetup -d /dev/loop0 # losetup /dev/loop1 journalfile And today it will fail: # mount /dev/sdb1 /mnt/test mount: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so # dmesg | tail -n 1 [17343.240702] EXT3-fs (sdb1): error: couldn't read superblock of external journal But with this new mount option, we can specify the new path: # mount -o journal_path=/dev/loop1 /dev/sdb1 /mnt/test # (which does update the encoded device number, incidentally): # umount /dev/sdb1 # dumpe2fs -h /dev/sdb1 | grep "Journal device" dumpe2fs 1.41.12 (17-May-2010) Journal device: 0x0701 But best of all we can just always mount by journal-path, and it'll always work: # mount -o journal_path=/dev/disk/by-label/mylabel-journal /dev/sdb1 /mnt/test # So the journal_path option can be specified in fstab, and as long as the disk is available somewhere, and findable by label (or by UUID), we can mount. Signed-off-by: Eric Sandeen --- The patch is a little hacky, doing all the work in option parsing, just to get to a journal devnum like the old option expected, only to later re-decode it when we really want to open it. I could clean it up so that both journal-update mount options find the bdev, rather than ending with an encoded device number, which must then be decoded & re-opened, if that seems better. But this was expedient enough to get the idea out on the list. If we like it, I'll do ext4 as well. Thanks, -Eric diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt index 293855e..7ed0d17 100644 --- a/Documentation/filesystems/ext3.txt +++ b/Documentation/filesystems/ext3.txt @@ -26,11 +26,12 @@ journal=inum When a journal already exists, this option is ignored. Otherwise, it specifies the number of the inode which will represent the ext3 file system's journal file. +journal_path=path journal_dev=devnum When the external journal device's major/minor numbers - have changed, this option allows the user to specify + have changed, these options allow the user to specify the new journal location. The journal device is - identified through its new major/minor numbers encoded - in devnum. + identified through either its new major/minor numbers + encoded in devnum, or via a path to the device. norecovery Don't load the journal on mounting. Note that this forces noload mount of inconsistent filesystem, which can lead to diff --git a/fs/ext3/super.c b/fs/ext3/super.c index c47f147..cb1dd6e 100644 --- a/fs/ext3/super.c +++ b/fs/ext3/super.c @@ -819,6 +819,7 @@ enum { Opt_user_xattr, Opt_nouser_xattr, Opt_acl, Opt_noacl, Opt_reservation, Opt_noreservation, Opt_noload, Opt_nobh, Opt_bh, Opt_commit, Opt_journal_update, Opt_journal_inum, Opt_journal_dev, + Opt_journal_path, Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback, Opt_data_err_abort, Opt_data_err_ignore, Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota, @@ -860,6 +861,7 @@ static const match_table_t tokens = { {Opt_journal_update, "journal=update"}, {Opt_journal_inum, "journal=%u"}, {Opt_journal_dev, "journal_dev=%u"}, + {Opt_journal_path, "journal_path=%s"}, {Opt_abort, "abort"}, {Opt_data_journal, "data=journal"}, {Opt_data_ordered, "data=ordered"}, @@ -975,6 +977,9 @@ static int parse_options (char *options, struct super_block *sb, int option; kuid_t uid; kgid_t gid; + struct block_device *journal_bdev; + char *journal_path; + #ifdef CONFIG_QUOTA int qfmt; #endif @@ -1129,6 +1134,31 @@ static int parse_options (char *options, struct super_block *sb, return 0; *journal_devnum = option; break; + case Opt_journal_path: + if (is_remount) { + ext3_msg(sb, KERN_ERR, "error: cannot specify " + "journal on remount"); + return 0; + } + journal_path = match_strdup(&args[0]); + if (!journal_path) { + ext3_msg(sb, KERN_ERR, "error: could not dup " + "journal device string"); + return 0; + } + journal_bdev = lookup_bdev(journal_path); + if (IS_ERR(journal_bdev)) { + ext3_msg(sb, KERN_ERR, "error: could not look " + "up journal device: error %d", + (int)PTR_ERR(journal_bdev)); + kfree(journal_path); + return 0; + } + + *journal_devnum = new_encode_dev(journal_bdev->bd_dev); + bdput(journal_bdev); + kfree(journal_path); + break; case Opt_noload: set_opt (sbi->s_mount_opt, NOLOAD); break;