linux-ext4 - Re: Scripting e2fsck: no errors, but still exit code 1 "FILE SYSTEM WAS MODIFIED"

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Message-ID: <20080520120953.GO15035@mit.edu>
Date:	Tue, 20 May 2008 08:09:53 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Bas van Schaik <bas@...es.nl>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Scripting e2fsck: no errors, but still exit code 1 "FILE
	SYSTEM WAS MODIFIED"

On Mon, May 19, 2008 at 01:32:53PM +0200, Bas van Schaik wrote:
> 
> Does this tell you anything?
> 

Unfortunately comparing the two dumpe2fs outputs don't show anything
interesting.  It did rule out a few cases where e2fsck can silently
mark the filesystem has having been modified (setting the directory
hash hint, moving the journal inode, which it does silently without
informing the user --- and I should fix that one of these days; I'll
create some bug reports to remind myself they need to be fixed), but I
don't see why it happened for your case.

It's definitely not normal; doing a journal replay does not cause fsck
to exit with a non-zero status, if it didn't make any other changes.
I just tested that with e2fsprogs 1.40.8 just in case something had
gotten screwed up, and it worked as expected.

I know how to debug it if you are really motiviated to get to the
bottom of this.  It would involve running a modified e2fsck/e2fsprogs
which changes ext2fs_mark_changed() and ext2fs_mark_super_dirty() to
be real functions, and setting breakpoints in gdb so we can trap any
calls made to those functions and dump out a stack backtrace, and then
continuing the e2fsck run, and then reporting to me the stack
backtraces where gdb trapped calls to ext2fs_mark_changed() and/or
ext2fs_mark_super_dirty().

Andreas is right though that if you are taking a proper snapshot, the
disk really should be quiesced and no journal replay should be
required at all.  That's how a devicemapper snapshot works in LVM ---
so one good question to explore is how *are* you doing your snapshots.

       	    	     		   - Ted
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