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ext4: 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.ext4 -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] EXT4-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: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
This commit is contained in:
Eric Sandeen 2013-08-28 19:05:07 -04:00 committed by Theodore Ts'o
parent bdfb6ff4a2
commit ad4eec6135
2 changed files with 48 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/filesystems/ext4.txt
View File

@ -144,11 +144,12 @@ journal_async_commit Commit block can be written to disk without waiting
mount the device. This will enable 'journal_checksum'
internally.
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
noload if the filesystem was not unmounted cleanly,

47
fs/ext4/super.c
View File

@ -1134,8 +1134,8 @@ enum {
Opt_nouid32, Opt_debug, Opt_removed,
Opt_user_xattr, Opt_nouser_xattr, Opt_acl, Opt_noacl,
Opt_auto_da_alloc, Opt_noauto_da_alloc, Opt_noload,
Opt_commit, Opt_min_batch_time, Opt_max_batch_time,
Opt_journal_dev, Opt_journal_checksum, Opt_journal_async_commit,
Opt_commit, Opt_min_batch_time, Opt_max_batch_time, Opt_journal_dev,
Opt_journal_path, Opt_journal_checksum, Opt_journal_async_commit,
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,
@ -1179,6 +1179,7 @@ static const match_table_t tokens = {
{Opt_min_batch_time, "min_batch_time=%u"},
{Opt_max_batch_time, "max_batch_time=%u"},
{Opt_journal_dev, "journal_dev=%u"},
{Opt_journal_path, "journal_path=%s"},
{Opt_journal_checksum, "journal_checksum"},
{Opt_journal_async_commit, "journal_async_commit"},
{Opt_abort, "abort"},
@ -1338,6 +1339,7 @@ static int clear_qf_name(struct super_block *sb, int qtype)
#define MOPT_NO_EXT2 0x0100
#define MOPT_NO_EXT3 0x0200
#define MOPT_EXT4_ONLY (MOPT_NO_EXT2 | MOPT_NO_EXT3)
#define MOPT_STRING 0x0400
static const struct mount_opts {
int token;
@ -1387,6 +1389,7 @@ static const struct mount_opts {
{Opt_resuid, 0, MOPT_GTE0},
{Opt_resgid, 0, MOPT_GTE0},
{Opt_journal_dev, 0, MOPT_GTE0},
{Opt_journal_path, 0, MOPT_STRING},
{Opt_journal_ioprio, 0, MOPT_GTE0},
{Opt_data_journal, EXT4_MOUNT_JOURNAL_DATA, MOPT_NO_EXT2 | MOPT_DATAJ},
{Opt_data_ordered, EXT4_MOUNT_ORDERED_DATA, MOPT_NO_EXT2 | MOPT_DATAJ},
@ -1480,7 +1483,7 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
return -1;
}
if (args->from && match_int(args, &arg))
if (args->from && !(m->flags & MOPT_STRING) && match_int(args, &arg))
return -1;
if (args->from && (m->flags & MOPT_GTE0) && (arg < 0))
return -1;
@ -1544,6 +1547,44 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
return -1;
}
*journal_devnum = arg;
} else if (token == Opt_journal_path) {
char *journal_path;
struct inode *journal_inode;
struct path path;
int error;
if (is_remount) {
ext4_msg(sb, KERN_ERR,
"Cannot specify journal on remount");
return -1;
}
journal_path = match_strdup(&args[0]);
if (!journal_path) {
ext4_msg(sb, KERN_ERR, "error: could not dup "
"journal device string");
return -1;
}
error = kern_path(journal_path, LOOKUP_FOLLOW, &path);
if (error) {
ext4_msg(sb, KERN_ERR, "error: could not find "
"journal device path: error %d", error);
kfree(journal_path);
return -1;
}
journal_inode = path.dentry->d_inode;
if (!S_ISBLK(journal_inode->i_mode)) {
ext4_msg(sb, KERN_ERR, "error: journal path %s "
"is not a block device", journal_path);
path_put(&path);
kfree(journal_path);
return -1;
}
*journal_devnum = new_encode_dev(journal_inode->i_rdev);
path_put(&path);
kfree(journal_path);
} else if (token == Opt_journal_ioprio) {
if (arg > 7) {
ext4_msg(sb, KERN_ERR, "Invalid journal IO priority"