XFS journal documentation?

XFS journal documentation?

[杨苏立 Yang Su Li]

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Hi,

I am trying to understand XFS a little bit better, especially its journal
process. Unfortunately, I am having trouble find documentation in this
regard.

The general XFS documentation (
http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/index.html)
has been quite helpful, but it doesn't describe the journal part of XFS. I
also found some kernel documentation ablout XFS's delayed logging (
https://www.kernel.org/doc/Documentation/filesystems/xfs-delayed-logging-design.txt),
which talks about the journal process a bit. But it seems to assume a lot
of prior knowledge of how the original XFS logging works to completely
understand what the author is talking about; and the term it uses (like
checkpoint) seem to have complete different meaning from, say, ext4.

So I am wondering, is there some kind of (any kind of ) documentation on
XFS journaling? Ideally it will cover the major data structure and major
code flow, but even a very high level, incomplete overview would be better
than what I have now, which is essentially nothing. And if so, where can I
find it?

Thanks a lot!

Suli

-- 
Suli Yang

Department of Physics
University of Wisconsin Madison

4257 Chamberlin Hall
Madison WI 53703

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Re: XFS journal documentation?

[Ben Myers]

Hi,

On Tue, Dec 03, 2013 at 02:55:23PM -0600, 杨苏立 Yang Su Li wrote:
> I am trying to understand XFS a little bit better, especially its journal
> process. Unfortunately, I am having trouble find documentation in this
> regard.
> 
> The general XFS documentation (
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/index.html)
> has been quite helpful, but it doesn't describe the journal part of XFS. I
> also found some kernel documentation ablout XFS's delayed logging (
> https://www.kernel.org/doc/Documentation/filesystems/xfs-delayed-logging-design.txt),
> which talks about the journal process a bit. But it seems to assume a lot
> of prior knowledge of how the original XFS logging works to completely
> understand what the author is talking about; and the term it uses (like
> checkpoint) seem to have complete different meaning from, say, ext4.
> 
> So I am wondering, is there some kind of (any kind of ) documentation on
> XFS journaling? Ideally it will cover the major data structure and major
> code flow, but even a very high level, incomplete overview would be better
> than what I have now, which is essentially nothing. And if so, where can I
> find it?

The original design docs are posted here:
http://oss.sgi.com/projects/xfs/design_docs/xfsdocs93_pdf/

log_mgr.pdf might be what you need.

Regards,
	Ben

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Re: XFS journal documentation?

[Dave Chinner]

On Tue, Dec 03, 2013 at 02:55:23PM -0600, 杨苏立 Yang Su Li wrote:
> Hi,
> 
> I am trying to understand XFS a little bit better, especially its journal
> process. Unfortunately, I am having trouble find documentation in this
> regard.
> 
> The general XFS documentation (
> http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/index.html)
> has been quite helpful, but it doesn't describe the journal part of XFS. I
> also found some kernel documentation ablout XFS's delayed logging (
> https://www.kernel.org/doc/Documentation/filesystems/xfs-delayed-logging-design.txt),
> which talks about the journal process a bit. But it seems to assume a lot
> of prior knowledge of how the original XFS logging works to completely
> understand what the author is talking about; and the term it uses (like
> checkpoint) seem to have complete different meaning from, say, ext4.

Yes, I assumed that the reader has some familiarity with XFS
journalling - it's documentation for XFS developers, not users...

> So I am wondering, is there some kind of (any kind of ) documentation on
> XFS journaling? Ideally it will cover the major data structure and major
> code flow, but even a very high level, incomplete overview would be better
> than what I have now, which is essentially nothing. And if so, where can I
> find it?

The code is your only really option. go look at
fs/xfs/xfs_log_format.h where all the structures that are formatted
into the log are defined, and xfs_log_recovery.c for how it is all
parsed....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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