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Re: [RFC PATCH 2/2] xfs: sysfs attributes for the current log state

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [RFC PATCH 2/2] xfs: sysfs attributes for the current log state
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Tue, 20 May 2014 07:17:06 -0400
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140519215658.GD8554@dastard>
References: <1400263966-35541-1-git-send-email-bfoster@xxxxxxxxxx> <1400263966-35541-3-git-send-email-bfoster@xxxxxxxxxx> <20140519215658.GD8554@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, May 20, 2014 at 07:56:58AM +1000, Dave Chinner wrote:
> On Fri, May 16, 2014 at 02:12:46PM -0400, Brian Foster wrote:
> > Create sysfs attributes to export the current runtime state of the log
> > to userspace. Note that the filesystem should be frozen for best
> > accuracy/consistency when reading these values, but is not required.
> > This is for testing and debug purposes only.
> > 
> > Create the following per-mount attributes: log_head_lsn, log_tail_lsn,
> > reserve_head_lsn and write_head_lsn. These represent the physical log
> 
> Reserve and write heads are not log sequence numbers (LSNs). A LSN
> is a cycle:block count tuple, while a grant head is a cycle:byte
> count tuple....
> 

Yeah, I suppose that's some terminology abuse... ;)

> Calling the reserve_grant_head/write_grant_head would make more
> sense, I think, as would splitting them into cycle/byte output
> pairs. Splitting them make sense because if we increase the log size
> beyond 2GB we're going to need a different in-memory representation
> for the grant heads (i.e. need more than 32 bits for byte count), so
> we should probably handle that up front in the sysfs API...
> 

Ok. reserve_grant_head and write_grant_head in the decimal format of
"cycle:bytes" it is. I'll leave the names of the others and convert them
to a similar "cycle:blocks" format. Thanks!

Brian

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@xxxxxxxxxxxxx

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