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Re: Hello, I have a question about XFS File System

To: Dave Chinner <david@xxxxxxxxxxxxx>, Yongmin <dev.yongmin@xxxxxxxxx>
Subject: Re: Hello, I have a question about XFS File System
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Fri, 07 Mar 2014 10:23:38 +0800
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140306225947.GM6851@dastard>
References: <195DE8C60CE24A62A71911FDE0B0DC97@xxxxxxxxx> <20140306225947.GM6851@dastard>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0

On 03/07 2014 06:59 AM, Dave Chinner wrote:
> On Thu, Mar 06, 2014 at 06:15:27PM +0900, Yongmin wrote:
>>
>> Hello.
>>
>> My name is Yongmin Park and I am a graduated student in Ajou University 
>> (Korea).
>> My research area is Digital Forensics.
>> And this time i tried to understand the structure of XFS file system, 
>> because XFS is one of the famous huge file system in these days.
>>
>> I already founded and read 'XFS Filesystem Structure 2nd Edition Revision 1' 
>> on the Internet, which was written by Silicon Graphics Inc in 2006 and it is 
>> really well written to understand.
>>
>> But the concentrated part of mine is "Deleted File Recovery", so the 
>> Journaling part is really important for me,, but regretfully there are no 
>> specific guide line about Journaling part...
>> Also next version(maybe the 3re Edition) is not exsist for more than a 5 
>> years.
>>
>> So is there no guide line for journaling part in XFS?
>> How can i get them,, have I to buy them? or Is Analysing Source Cord only 
>> way to study?
> 
> There is some documentation about some of the logging concepts and
> design. eg:
> 
> http://oss.sgi.com/cgi-bin/gitweb.cgi?p=xfs/xfs-documentation.git;a=blob;f=design/xfs-delayed-logging-design.asciidoc

Not sure if someone else also think that XFS journal design is the 
stumbling-block
to get involved into the development...but I once heard of "I'm really confused 
by
the design of delayed logging, I have to give up after reading the document for 
about
2 or 3 weeks..." from 2 Chinese developers in the past year, though nothing can 
help
someone out without taking infinite patience.

> 
> But the only way to learn about the actual structure of the log is to
> read the code and use xfs_logprint to study the contents of the log.

To Yongmin,

For your information only.

I'm trying to understand XFS journal via the following steps:

1) Download Linux-2.6.34 source, read the journal code.
Understand the original design as there is no delayed-logging support at that 
time.

FYI, two obsoleted documents could be found at,
http://oss.sgi.com/projects/xfs/design_docs/xfsdocs93_pdf/log_mgr-overview.pdf
http://oss.sgi.com/projects/xfs/design_docs/xfsdocs93_pdf/log_mgr.pdf

2) Download Linux-2.6.35 source, read the journal code and 
delayed-logging-design doc as
per Dave's suggestion because we have this big change in this version.

3) Play with xfs_logprint with the XFS mainline source and read all those 
threads in XFS
mailing list which are related to journals in the past several years....

4) Nothing, just have fun. :)


Thanks,
-Jeff

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