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authorEric Sandeen <sandeen@redhat.com>2013-07-31 21:33:00 +0200
committerJan Kara <jack@suse.cz>2013-07-31 22:11:15 +0200
commitcf7eff4666629de006c5ed78de79e40f483c3b06 (patch)
tree83248c91e87f0716c967414cb110340baca1d7c1 /Documentation
parentjbd: remove unneeded semicolon (diff)
downloadlinux-cf7eff4666629de006c5ed78de79e40f483c3b06.tar.xz
linux-cf7eff4666629de006c5ed78de79e40f483c3b06.zip
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 ... 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@redhat.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/ext3.txt7
1 files changed, 4 insertions, 3 deletions
diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
index 293855e95000..7ed0d17d6721 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