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Message-ID: <20130807103135.GA12843@quack.suse.cz> Date: Wed, 7 Aug 2013 12:31:35 +0200 From: Jan Kara <jack@...e.cz> To: Eric Sandeen <sandeen@...hat.com> Cc: ext4 development <linux-ext4@...r.kernel.org> Subject: Re: [PATCH V2] ext4: allow specifying external journal by pathname mount option On Wed 31-07-13 17:20:29, Eric Sandeen wrote: > 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@...hat.com> The patch looks good. You can add: Reviewed-by: Jan Kara <jack@...e.cz> Honza > --- > > V2: grr, remove debug printk, sorry :/ > > p.s. is there any point to MOPT_GTE0? Doesn't the "=%u" token parsing > exclude negative numbers? > > I hate to add the MOPT_STRING, but since we try to grab arguments > outside the case statement, I guess it's required... > > -Eric > > > > 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 bca26f3..2f5ce3a 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" > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jan Kara <jack@...e.cz> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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