Wrong Data Pointer-XFS File system

Wrong Data Pointer-XFS File system

[Sandy1]

Hi,
I am Using SuSe 10.0 with Xfs file system. I am working on a File system
based project. During the initial research in On disk layout of File system
, i found data pointer problem. I was not able to get the data location as
per pointed by "absolute block no." in "xfs_bmbt_rec" extent pointers.

When i create any file in 0th (zero`th) AG in that case i am able to reach
on proper location by using "absolute block no." pointer.

But when i create any file in 1st or in 2nd AG and so on. I never got the
file data at the location pointed by "absolute block no.". I always found
the file data before the the pointed address.

I am not getting any value in Superblock that tells me about difference in
pointer location with actual data.

This value always becomes multiple of the AG number.

Please help to get out from this problem.

Is there any other calculation for finding the data locations.

I am right now consulting the Doument issued by SGI caleed "XFS file system
Structure" 2nd Edition.

Regards

Sandy

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Re: Wrong Data Pointer-XFS File system

[David Chinner]

On Thu, Jun 21, 2007 at 11:23:35PM -0700, Sandy1 wrote:
> 
> Hi,
> I am Using SuSe 10.0 with Xfs file system. I am working on a File system
> based project. During the initial research in On disk layout of File system
> , i found data pointer problem. I was not able to get the data location as
> per pointed by "absolute block no." in "xfs_bmbt_rec" extent pointers.

The xfs_bmbt_rec holds the address in FSB format, not DADDR format.

> When i create any file in 0th (zero`th) AG in that case i am able to reach
> on proper location by using "absolute block no." pointer.
> 
> But when i create any file in 1st or in 2nd AG and so on. I never got the
> file data at the location pointed by "absolute block no.". I always found
> the file data before the the pointed address.

FSB notation is sparse representation.

> I am not getting any value in Superblock that tells me about difference in
> pointer location with actual data.
> 
> This value always becomes multiple of the AG number.
> 
> Please help to get out from this problem.
> 
> Is there any other calculation for finding the data locations.

man xfs_db. Search for "convert".

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group

Re: Wrong Data Pointer-XFS File system

[Sandy1]

Hi David,

I am already using FSB format, i am using this format for sparsing the
absolute block number,
as we know extent is 128 bit in size and uses the following packed layout:

LSB... bit 0-20              gives # blocks
        bits 21 to 72 (52)  gives absolute number
        bits 72 to 126 (54) gives logical file block offset
MSB..flag(last bit)

the value i am getting in absolute no. is in FSB and after multiplying with
no. of sectors in FS block i am trying to jump that value (pointer
location). But only in 0th AG i am able to get the data.Afterwards i am not
able to reach the data in next AGs.

I also read in document that "sb_agblklog"--> This value is used to generate
inode numbers and absolute block numbers defined in extent maps.

How i can use this value in interprating the absolute block number?

Is the above sparsing method is right or there is any other calculation?
Please guide me.

Regards
Sandy





David Chinner wrote:
> 
> On Thu, Jun 21, 2007 at 11:23:35PM -0700, Sandy1 wrote:
>> 
>> Hi,
>> I am Using SuSe 10.0 with Xfs file system. I am working on a File system
>> based project. During the initial research in On disk layout of File
>> system
>> , i found data pointer problem. I was not able to get the data location
>> as
>> per pointed by "absolute block no." in "xfs_bmbt_rec" extent pointers.
> 
> The xfs_bmbt_rec holds the address in FSB format, not DADDR format.
> 
>> When i create any file in 0th (zero`th) AG in that case i am able to
>> reach
>> on proper location by using "absolute block no." pointer.
>> 
>> But when i create any file in 1st or in 2nd AG and so on. I never got the
>> file data at the location pointed by "absolute block no.". I always found
>> the file data before the the pointed address.
> 
> FSB notation is sparse representation.
> 
>> I am not getting any value in Superblock that tells me about difference
>> in
>> pointer location with actual data.
>> 
>> This value always becomes multiple of the AG number.
>> 
>> Please help to get out from this problem.
>> 
>> Is there any other calculation for finding the data locations.
> 
> man xfs_db. Search for "convert".
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> Principal Engineer
> SGI Australian Software Group
> 
> 
> 
> 

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