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Date:	Tue, 31 Jan 2012 14:43:41 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Akira Fujita <a-fujita@...jp.nec.com>
CC:	Theodore Tso <tytso@....edu>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [BUG] e2fsprogs: e2fsck -b outputs checksum warnings

On 9/7/11 3:10 AM, Akira Fujita wrote:
> Hi,
> 
> With e2fsck -b option, we can use an alternative
> superblock instead of the normal superblock.
> However it shows some warnings, especially checksum warnings
> appear when we do e2fsck -b every time.

I looked into this a little bit, and the reason the checksums differ
is because the b_flags & bg_itable_unused values differ from mkfs
time vs. e2fsck time.  This is due to this bit of code in
lib/ext2fs/openfs.c:

        /*
         * If recovery is from backup superblock, Clear _UNININT flags &
         * reset bg_itable_unused to zero
         */
        if (superblock > 1 && EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
                                        EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
                dgrp_t group;

                for (group = 0; group < fs->group_desc_count; group++) {
                        ext2fs_bg_flags_clear(fs, group, EXT2_BG_BLOCK_UNINIT);
                        ext2fs_bg_flags_clear(fs, group, EXT2_BG_INODE_UNINIT);
                        ext2fs_bg_itable_unused_set(fs, group, 0);
                }
                ext2fs_mark_super_dirty(fs);
        }

This makes the group look like it is initialized and that all inodes are used.

Can someone remind me why we want to do this?

-Eric

> Test environment:
> - kernel 3.1.0-rc3
> - e2fsprogs (commit:d4c0d8e5b858cdf3d3000f2b3fca532787f34a02)
> 
> # mkfs -t ext4 /dev/sda8
> # e2fsck -b 32768 /dev/sda8
> e2fsck 1.42-WIP (02-Jul-2011)
> One or more block group descriptor checksums are invalid.  Fix<y>? yes
> 
> Group descriptor 0 checksum is invalid.  FIXED.
> Group descriptor 1 checksum is invalid.  FIXED.
> Group descriptor 2 checksum is invalid.  FIXED.
> Group descriptor 3 checksum is invalid.  FIXED.
> Group descriptor 4 checksum is invalid.  FIXED.
> Group descriptor 5 checksum is invalid.  FIXED.
> Group descriptor 6 checksum is invalid.  FIXED.
> Group descriptor 7 checksum is invalid.  FIXED.
> Group descriptor 8 checksum is invalid.  FIXED.
> Group descriptor 9 checksum is invalid.  FIXED.
> Group descriptor 10 checksum is invalid.  FIXED.
> Group descriptor 11 checksum is invalid.  FIXED.
> Group descriptor 12 checksum is invalid.  FIXED.
> Group descriptor 13 checksum is invalid.  FIXED.
> Group descriptor 14 checksum is invalid.  FIXED.
> Group descriptor 15 checksum is invalid.  FIXED.
> Group descriptor 16 checksum is invalid.  FIXED.
> Group descriptor 17 checksum is invalid.  FIXED.
> Group descriptor 18 checksum is invalid.  FIXED.
> Group descriptor 19 checksum is invalid.  FIXED.
> Group descriptor 20 checksum is invalid.  FIXED.
> Group descriptor 21 checksum is invalid.  FIXED.
> Group descriptor 22 checksum is invalid.  FIXED.
> Group descriptor 23 checksum is invalid.  FIXED.
> Group descriptor 24 checksum is invalid.  FIXED.
> Group descriptor 25 checksum is invalid.  FIXED.
> Group descriptor 26 checksum is invalid.  FIXED.
> Group descriptor 27 checksum is invalid.  FIXED.
> Group descriptor 28 checksum is invalid.  FIXED.
> Group descriptor 29 checksum is invalid.  FIXED.
> Group descriptor 30 checksum is invalid.  FIXED.
> Group descriptor 31 checksum is invalid.  FIXED.
> /dev/sda8 contains a file system with errors, check forced.
> 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
> Block bitmap differences:  -(65600--65602) -(65611--65612) -(65621--65622) -(65625--65627) -65630 -(65632--65634) -(65643--65644) -(65653--65654) -(65657--65659) -65662 -(65664--65666) -(65675--65676)
> -(65685--65686) -(65689--65691) -65694 -67584 -(67586--67587) -(67589--67592) -67598 -67628 -(67648--67650) -(67659--67660) -(67669--67670) -(67673--67675) -67678 -(67680--67682) -(67691--67692)
> -(67701--67702) -(67705--67707) -67710 -(67712--67714) -(67723--67724) -(67733--67734) -(67737--67739) -67742 -(67792--67793) -67811 -(67904--67905) -(67912--67913) -(68610--68612) -(68736--68738)
> -(68747--68748) -(68757--68758) -(68761--68763) -68766 -(77831--77832) -77839 -(77870--77871) -77878 -(77888--77890) -(77899--77900) -(77909--77910) -(77913--77915) -77918 -(77920--77922)
> -(77931--77932) -(77941--77942) -(77945--77947) -77950 -(77952--77954) -(77963--77964) -(77973--77974) -(77977--77979) -77982 -78032 -78051 -(78054--78061) -78563 -(78568--78569) -78688
> -(78850--78852) -(78976--78978) -(78987--78988) -(78997--78998) -(79001--79003) -79006 -(79879--79880) -79887 -79931 -(79936--79938) -(79947--79948) -(79957--79958) -(79961--79963) -79966
> -(79968--79970) -(79979--79980) -(79989--79990) -(79993--79995) -79998 -(80000--80002) -(80011--80012) -(80021--80022) -(80025--80027) -80030 -80080 -80099 -80104 -80114 -80193 -80201 -(80207--80210)
> -(80224--80225) -80233 -(80239--80242) -80258 -80265 -(80271--80274) -80288 -80290 -80297 -(80303--80306) -(80321--80322) -80329 -(80335--80338) -(80352--80354) -80361 -(80367--80370) -80387 -80393
> -(80399--80402) -80416 -80419 -80425 -(80431--80434) -80449 -80451 -80457 -(80463--80466) -(80480--80481) -80483 -80489 -(80495--80498) -(80514--80515) -80521 -(80527--80530) -80544 -(80546--80547)
> -80553 -(80559--80562) -(80577--80579) -80585 -(80591--80594) -(80608--80611) -(80617--80618) -(80623--80626) -(80898--80900) -(81024--81026) -(81035--81036) -(81045--81046) -(81049--81051) -81054
> -(86022--86024) -86030 -86062 -(86080--86082) -(86091--86092) -(86101--86102) -(86105--86107) -86110 -(86112--86114) -(86123--86124) -(86133--86134) -(86137--86139) -86142 -(86144--86146)
> -(86155--86156) -(86165--86166) -(86169--86171) -86174 -86225 -86245 -86338 -(86344--86345) -86368 -86370 -(86376--86377) -(86401--86402) -(86408--86409) -(86432--86434) -(86440--86441)
> -(87042--87044) -(87168--87170) -(87179--87180) -(87189--87190) -(87193--87195) -87198 -(565248--589823)
> Fix<y>? yes
> 
> 
> /dev/sda8: ***** FILE SYSTEM WAS MODIFIED *****
> /dev/sda8: 11/262144 files (0.0% non-contiguous), 51278/1048576 blocks
> 
> 
> Regards,
> Akira Fujita
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