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Message-ID: <51F83D90.5080708@redhat.com>
Date: Tue, 30 Jul 2013 17:26:24 -0500
From: Eric Sandeen <sandeen@...hat.com>
To: ext4 development <linux-ext4@...r.kernel.org>,
Jan Kara <jack@...e.cz>
CC: Leonardo Menezes Vaz <lvaz@...hat.com>
Subject: [PATCH] ext3: allow specifying external journal by pathname mount
option
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 <sandeen@...hat.com>
---
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;
--
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