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Re: xfs_bmbt_rec_64 leading to wrong blocks

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: xfs_bmbt_rec_64 leading to wrong blocks
From: Felipe Monteiro de Carvalho <felipemonteiro.carvalho@xxxxxxxxx>
Date: Wed, 6 Aug 2014 14:31:11 +0200
Cc: xfs@xxxxxxxxxxx
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Thanks! Indeed that's it =)

One strange thing however is that in my xfs_dir2_data.h there is:

#define XFS_DIR2_DATA_ALIGN_LOG 3 /* i.e., 8 bytes */
#define XFS_DIR2_SPACE_SIZE (1ULL << (32 + XFS_DIR2_DATA_ALIGN_LOG))
#define XFS_DIR2_LEAF_SPACE 1
#define XFS_DIR2_LEAF_OFFSET (XFS_DIR2_LEAF_SPACE * XFS_DIR2_SPACE_SIZE)

That doesn't match the number that I am seeing here for the offset.
Here I see 1 << 23, but according to the headers it should be 1 << 35

--
Felipe Monteiro de Carvalho


On Wed, Aug 6, 2014 at 1:34 PM, Brian Foster <bfoster@xxxxxxxxxx> wrote:
> On Wed, Aug 06, 2014 at 12:12:12PM +0200, Felipe Monteiro de Carvalho wrote:
>> Hello,
>>
>> I am writing a software which reads xfs partitions and it is working
>> well so far, but, at in a particular folder with 10k files, only 7k
>> files appear, the other ones don't.
>>
>> I read an inode which has di_core.di_format = XFS_DINODE_FMT_BTREE
>>
>> No problem here, the btree is trivial, it has only 1 element inside
>> it, which leads to a list of 82 extends.
>>
>> Extends 0..52 aprox. are all great, and work fine.
>>
>> Extent 53 (and other ones after that) point to very wierd memory areas
>> which don't match the pattern that I saw previously =(
>>
>> Here is the hex data of the extents, the selected extent in nr 53:
>>
>> http://magnifier.sourceforge.net/temp/xfs/extent_with_xfs_bmbt_rec_64.png
>>
>> And here is debug information showing which values I extracted from this 
>> table:
>>
>> i=0 FLocalExtent.StartOff=0 FLocalExtent.StartBlock=66748
>> FLocalExtent.BlockCount=1 lStartBlock=65212
>> i=1 FLocalExtent.StartOff=1 FLocalExtent.StartBlock=66758
>> FLocalExtent.BlockCount=2 lStartBlock=65222
>> i=2 FLocalExtent.StartOff=3 FLocalExtent.StartBlock=66772
>> FLocalExtent.BlockCount=1 lStartBlock=65236
>> ....
>>
>> i=51 FLocalExtent.StartOff=77 FLocalExtent.StartBlock=67468
>> FLocalExtent.BlockCount=1 lStartBlock=65932
>> i=52 FLocalExtent.StartOff=78 FLocalExtent.StartBlock=67479
>> FLocalExtent.BlockCount=1 lStartBlock=65943
>> i=53 FLocalExtent.StartOff=8388608 FLocalExtent.StartBlock=66749
>> FLocalExtent.BlockCount=1 lStartBlock=65213
>> i=54 FLocalExtent.StartOff=8388609 FLocalExtent.StartBlock=66783
>> FLocalExtent.BlockCount=2 lStartBlock=65247
>> ...
>>
>> Note how StartOff is suddenly so big! But I manually checked the bits
>> comparing to xfs_bmbt_rec_64 and the value written is that one. But
>> what sense does it make for StartOff to jump like that?
>>
>
> Assuming 4k blocks, 8388608 is 32G, which is the offset interval used
> for some internal sections of directories on XFS. If this is a
> directory, it could be a node/leaf or freelist block. Looking at
> xfs_da_format.h, it looks like XFS_DIR2_LEAF_OFFSET points to this
> offset. This block basically points to a btree of hashed entry names for
> lookup. See here for basics:
>
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/Directories.html
>
> ... and here for a diagram:
>
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/Node_Directories.html
>
>> And why are the blocks pointing to a non-XD2D block?
>>
>> Here is the block to which one of the valid extents point to:
>>
>> http://magnifier.sourceforge.net/temp/xfs/correct_block_xd2d.png
>>
>> And here is a block to which one of the extents that I cannot
>> interpretate point to:
>>
>> http://magnifier.sourceforge.net/temp/xfs/wierd_block_xd2d.png
>> and another one:
>> http://magnifier.sourceforge.net/temp/xfs/wierd_xfs_dir2_data_entry.png
>>
>
> The 0xFEBE magic seems to confirm the second one as a node block.
>
> Brian
>
>> Any ideas???
>>
>> I already worked so much on this, but I cannot figure out =(
>>
>> thanks,
>> --
>> Felipe Monteiro de Carvalho
>>
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-- 
Felipe Monteiro de Carvalho

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