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ext4: allow specifying external journal by pathname mount option

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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
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47
fs/ext4/super.c
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@@ -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"