Re: [PATCH 3/4 v3] tune2fs: update journal super block when changing UUID for fs.

On Jul 31, 2014, at 17:45, Azat Khuzhin [off-list ref] wrote:

quoted

On Thu, Jul 31, 2014 at 10:16:44AM -0500, Eric Sandeen wrote:

quoted

On 7/28/14, 2:43 AM, Azat Khuzhin wrote:
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 <redacted>
Signed-off-by: Azat Khuzhin <redacted>
Reviewed-by: Andreas Dilger <redacted>
---
misc/tune2fs.c | 74 ++++++++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 56 insertions(+), 18 deletions(-)

diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 1df655a..74e57ae 100644
--- 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);

This is already committed (which is why Coverity whined about it), but:
removing this assignment causes an uninitialized use of "start" later
in this function:

       /* Write back the journal superblock */
       if ((retval = io_channel_write_blk64(jfs->io, start,
           -SUPERBLOCK_SIZE, buf)))

-Eric

Hi Eric,

Thanks for catching this.
Patch in attachment must fix this issue.

I maked with -Wall to catch more bugs like this.
And there is one more note:
expected ‘char *’ but argument is of type ‘__u8 *’
journal_user()
I will send a patch later.


From 903f251e1ebce3d666a8b2af04b812d4f6751056 Mon Sep 17 00:00:00 2001
From: Azat Khuzhin <redacted>
Date: Thu, 31 Jul 2014 19:26:16 +0400
Subject: [PATCH] tune2fs: initialize start block in remove_journal_device()

---
misc/tune2fs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 0c1feb1..044daaf 100644
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c

@@ -181,7 +181,6 @@ static __u32 clear_ok_features[3] = {

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 &

@@ -286,6 +285,7 @@ static int remove_journal_device(ext2_filsys fs)
   jsb->s_nr_users = htonl(nr_users);

   /* Write back the journal superblock */
+    start = ext2fs_journal_sb_start(jfs->blocksize);
   if ((retval = io_channel_write_blk64(jfs->io, start,
       -SUPERBLOCK_SIZE, buf))) {
       com_err(program_name, retval,

-- 
2.0.1