From ad4eec613536dc7e5ea0c6e59849e6edca634d8b Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Wed, 28 Aug 2013 19:05:07 -0400 Subject: [PATCH] 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 Signed-off-by: "Theodore Ts'o" Reviewed-by: Jan Kara Reviewed-by: Carlos Maiolino --- Documentation/filesystems/ext4.txt | 7 +++--- fs/ext4/super.c | 47 +++++++++++++++++++++++++++++++++++--- 2 files changed, 48 insertions(+), 6 deletions(-) diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index f7cbf57..b91cfaa 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -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, diff --git a/fs/ext4/super.c b/fs/ext4/super.c index b59373b..4233714 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -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" -- 2.7.4