linux-ext4 - Re: [PATCH] e2fsck shouln't consider superblock summaries as fatal

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Message-id: <20080826212743.GP3392@webber.adilger.int>
Date:	Tue, 26 Aug 2008 15:27:43 -0600
From:	Andreas Dilger <adilger@....com>
To:	Theodore Tso <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] e2fsck shouln't consider superblock summaries as fatal

On Aug 26, 2008  13:04 -0400, Theodore Ts'o wrote:
> On Tue, Aug 26, 2008 at 04:45:02AM -0600, Andreas Dilger wrote:
> > Running e2fsck on a quiescent (but mounted) filesystem fails in the
> > common case where the superblock inode and block count summaries are
> > wrong.  The kernel doesn't update these values except at unmount time.
> > If there are other errors in the filesystem then they will already
> > cause e2fsck to consider the filesystem invalid, so these minor errors
> > should not.
> 
> Sure, but *when* would it ever be safe to run e2fsck without -n on a
> mounted filesystem?  What's the scenario where this would matter?  And
> on an unmounted filesystem, if the block counts are wrong, and the
> user refuses to fix them the filesystem technically really isn't 100%
> valid.

I mean that this is for "e2fsck -fn".  In that case the filesystem isn't
changed, and is often completely clean except the superblock counters.
Until we have block-device freeze ioctl widely available (or convince
users to use LVM), the best we can do is quiesce Lustre IO without
unmounting the filesystem.

Without patch:

# e2fsck -fn /dev/hda3
e2fsck 1.40.7.sun1 (28-Feb-2008)
Warning!  /dev/hda3 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong (213908, counted=213298).
Fix? no

Free inodes count wrong (249992, counted=249282).
Fix? no

lustre-MDT0000: ********** WARNING: Filesystem still has errors **********

lustre-MDT0000: 56/250048 files (17.9% non-contiguous), 36092/250000 blocks

# echo $?
4

With patch:

# e2fsck -fn /dev/hda3
e2fsck 1.40.11.sun1 (17-June-2008)
Warning!  /dev/hda3 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong (213908, counted=213298).
Fix? no

Free inodes count wrong (249992, counted=249282).
Fix? no

lustre-MDT0000: 56/250048 files (17.9% non-contiguous), 36092/250000 blocks
# echo $?
0

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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