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.
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
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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On Tue, Jan 31, 2012 at 02:43:41PM -0600, Eric Sandeen wrote:
> /*
> * If recovery is from backup superblock, Clear _UNININT flags &
> * reset bg_itable_unused to zero
> */
>
> 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?
It's because the kernel don't update the backup block group
descriptors. So there may very well be bitmaps that have since been
initialized and in use, and there may very well be inodes that have
been allocated that are not represented by the value of
bg_itable_unused in the backup bg descriptors. And the inode iterator
functions will simply skip inodes that are marked as not in use;
indeed, that's one of the ways we speed up fsck times; by skipping
portions of the inode table that are not in use. The problem is that
if the primary superblock and block group descriptors are corrupt, we
don't know which portions of the inode table are in use and which are
not.
This is also why the lazy itable init code is so important; if we're
going to skip zero'ing the inode table, then until the inode table
gets initialized, we are at risk of finding old inodes from previous
file systems that had been on the storage device in the case where we
are using backup bg descriptors and/or the checksums are incorrect.
This doesn't happen that often, but it's still important that the
inode table get appropriately initialized, which is why it may be ok
for a distro installer to disable the lazy itable init to speed up the
install process, but you still want to let the lazy itable process
finish up as soon as possible.
> > 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.
This is certainly scary, though. In the case where we do need to use
the backup block group descriptors, it would be better to reset the
checksum to the correct value so we don't get all of this extra
output, which isn't useful to the user and is just going to alarm them
unnecessarily.
- Ted
On 2012-01-31, at 1:56 PM, Ted Ts'o wrote:
>>> 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.
>
> This is certainly scary, though. In the case where we do need to use
> the backup block group descriptors, it would be better to reset the
> checksum to the correct value so we don't get all of this extra
> output, which isn't useful to the user and is just going to alarm them
> unnecessarily.
I was thinking this is just an oversight in the code which is removing the
UNINIT flags. It should just recompute the group checksum (which will
happen only rarely, and the performance isn't critical).
A patch has been submitted separately.
Cheers, Andreas