Commit cf7eff46 authored by Eric Sandeen's avatar Eric Sandeen Committed by Jan Kara
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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: default avatarEric Sandeen <sandeen@redhat.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
parent 75b92225

Documentation/filesystems/ext3.txt

+4 −3
Original line number Diff line number Diff line
@@ -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

fs/ext3/super.c

+43 −0
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <linux/seq_file.h>

#include <linux/log2.h>

#include <linux/cleancache.h>

#include <linux/namei.h>



#include <asm/uaccess.h>
@@ -819,6 +820,7 @@ 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 +862,7 @@ 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 +978,11 @@ static int parse_options (char *options, struct super_block *sb, 
	int option;

	kuid_t uid;

	kgid_t gid;

	char *journal_path;

	struct inode *journal_inode;

	struct path path;

	int error;



#ifdef CONFIG_QUOTA

	int qfmt;

#endif
@@ -1129,6 +1137,41 @@ 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;

			}



			error = kern_path(journal_path, LOOKUP_FOLLOW, &path);

			if (error) {

				ext3_msg(sb, KERN_ERR, "error: could not find "

					"journal device path: error %d", error);

				kfree(journal_path);

				return 0;

			}



			journal_inode = path.dentry->d_inode;

			if (!S_ISBLK(journal_inode->i_mode)) {

				ext3_msg(sb, KERN_ERR, "error: journal path %s "

					"is not a block device", journal_path);

				path_put(&path);

				kfree(journal_path);

				return 0;

			}



			*journal_devnum = new_encode_dev(journal_inode->i_rdev);

			path_put(&path);

			kfree(journal_path);

			break;

		case Opt_noload:

			set_opt (sbi->s_mount_opt, NOLOAD);

			break;

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