tune2fs: update journal super block when changing UUID for fs.

Using -U option you can change the UUID for fs, however it will not work
for journal device, since it have a copy of this UUID inside jsb (i.e.
journal super block). So copy UUID on change into that block.

Here is the initial thread:
http://comments.gmane.org/gmane.comp.file-systems.ext4/44532

You can reproduce this by executing following commands:
$ fallocate -l100M /tmp/dev
$ fallocate -l100M /tmp/journal
$ sudo /sbin/losetup /dev/loop1 /tmp/dev
$ sudo /sbin/losetup /dev/loop0 /tmp/journal
$ mke2fs -O journal_dev /tmp/journal
$ tune2fs -U da1f2ed0-60f6-aaaa-92fd-738701418523 /tmp/journal
$ sudo mke2fs -t ext4 -J device=/dev/loop0 /dev/loop1
$ dumpe2fs -h /tmp/dev | fgrep UUID
dumpe2fs 1.43-WIP (18-May-2014)
Filesystem UUID:          8a776be9-12eb-411f-8e88-b873575ecfb6
Journal UUID:             e3d02151-e776-4865-af25-aecb7291e8e5
$ sudo e2fsck /dev/vdc
e2fsck 1.43-WIP (18-May-2014)
External journal does not support this filesystem

/dev/loop1: ********** WARNING: Filesystem still has errors **********

Reported-by: Chin Tzung Cheng <chintzung@gmail.com>
Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 1df655a..74e57ae 100644 (file)
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c
@@ -175,6 +175,38 @@ static __u32 clear_ok_features[3] = {
                EXT4_FEATURE_RO_COMPAT_GDT_CSUM
 };
 
+/**
+ * Try to get journal super block if any
+ */
+static int get_journal_sb(ext2_filsys jfs, char buf[SUPERBLOCK_SIZE])
+{
+       int retval;
+       int start;
+       journal_superblock_t *jsb;
+
+       if (!(jfs->super->s_feature_incompat &
+           EXT3_FEATURE_INCOMPAT_JOURNAL_DEV)) {
+               return EXT2_ET_UNSUPP_FEATURE;
+       }
+
+       /* Get the journal superblock */
+       if ((retval = io_channel_read_blk64(jfs->io,
+           ext2fs_journal_sb_start(jfs->blocksize), -SUPERBLOCK_SIZE, buf))) {
+               com_err(program_name, retval, "%s",
+               _("while reading journal superblock"));
+               return retval;
+       }
+
+       jsb = (journal_superblock_t *) buf;
+       if ((jsb->s_header.h_magic != (unsigned)ntohl(JFS_MAGIC_NUMBER)) ||
+           (jsb->s_header.h_blocktype != (unsigned)ntohl(JFS_SUPERBLOCK_V2))) {
+               fputs(_("Journal superblock not found!\n"), stderr);
+               return EXT2_ET_BAD_MAGIC;
+       }
+
+       return 0;
+}
+
 /*
  * Remove an external journal from the filesystem
  */
@@ -218,29 +250,15 @@ static int remove_journal_device(ext2_filsys fs)
                        _("while trying to open external journal"));
                goto no_valid_journal;
        }
-       if (!(jfs->super->s_feature_incompat &
-             EXT3_FEATURE_INCOMPAT_JOURNAL_DEV)) {
-               fprintf(stderr, _("%s is not a journal device.\n"),
-                       journal_path);
-               goto no_valid_journal;
-       }
 
-       start = ext2fs_journal_sb_start(fs->blocksize);
-       /* Get the journal superblock */
-       if ((retval = io_channel_read_blk64(jfs->io, start,
-           -SUPERBLOCK_SIZE, buf))) {
-               com_err(program_name, retval, "%s",
-                       _("while reading journal superblock"));
+       if ((retval = get_journal_sb(jfs, buf))) {
+               if (retval == EXT2_ET_UNSUPP_FEATURE)
+                       fprintf(stderr, _("%s is not a journal device.\n"),
+                               journal_path);
                goto no_valid_journal;
        }
 
        jsb = (journal_superblock_t *) buf;
-       if ((jsb->s_header.h_magic != (unsigned)ntohl(JFS_MAGIC_NUMBER)) ||
-           (jsb->s_header.h_blocktype != (unsigned)ntohl(JFS_SUPERBLOCK_V2))) {
-               fputs(_("Journal superblock not found!\n"), stderr);
-               goto no_valid_journal;
-       }
-
        /* Find the filesystem UUID */
        nr_users = ntohl(jsb->s_nr_users);
        for (i = 0; i < nr_users; i++) {
@@ -2184,6 +2202,7 @@ retry_open:
        if (U_flag) {
                int set_csum = 0;
                dgrp_t i;
+               char buf[SUPERBLOCK_SIZE];
 
                if (sb->s_feature_ro_compat &
                    EXT4_FEATURE_RO_COMPAT_GDT_CSUM) {
@@ -2229,6 +2248,25 @@ retry_open:
                                ext2fs_group_desc_csum_set(fs, i);
                        fs->flags &= ~EXT2_FLAG_SUPER_ONLY;
                }
+
+               /* If this is a journal dev, we need to copy UUID into jsb */
+               if (!(rc = get_journal_sb(fs, buf))) {
+                       journal_superblock_t *jsb;
+
+                       jsb = (journal_superblock_t *) buf;
+                       fputs(_("Need to update journal superblock.\n"), stdout);
+                       memcpy(jsb->s_uuid, sb->s_uuid, sizeof(sb->s_uuid));
+
+                       /* Writeback the journal superblock */
+                       if ((rc = io_channel_write_blk64(fs->io,
+                               ext2fs_journal_sb_start(fs->blocksize),
+                                       -SUPERBLOCK_SIZE, buf)))
+                               goto closefs;
+               } else if (rc != EXT2_ET_UNSUPP_FEATURE)
+                       goto closefs;
+               else
+                       rc = 0; /** Reset rc to avoid ext2fs_mmp_stop() */
+
                ext2fs_mark_super_dirty(fs);
        }
        if (I_flag) {