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

[Azat Khuzhin <a3at.mail@gmail.com>]

On Thu, Jul 31, 2014 at 10:16:44AM -0500, Eric Sandeen wrote:
> 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 <chintzung@gmail.com>
> > Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>
> > Reviewed-by: Andreas Dilger <adilger@dilger.ca>
> > ---
> >  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 <a3at.mail@gmail.com>
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

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