From: Andreas Dilger <adilger@sun.com>
Subject: Re: Tool to view extent metadata
Date: Thu, 09 Jul 2009 16:55:07 -0600
Message-ID: <20090709225507.GH5073@webber.adilger.int>
References: <23904f640907091517w10608fa4y9b3b8b3a631217c@mail.gmail.com>
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Cc: linux-ext4@vger.kernel.org
To: Manuel Benitez <rickyb@google.com>
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On Jul 09, 2009  15:17 -0700, Manuel Benitez wrote:
> I'm currently evaluating the ext4 allocator and one thing I've come
> across is the lack of a tool that displays the exact structure of the
> extents making up a file. I've found plenty of tools that will tell me
> how many contiguous segments a file contains, but nothing so far to
> let me see the actual makeup of the extents that map the inode to the
> blocks that comprise the file. Have I just missed something obvious,
> or would this be something worth me spending some time doing?
> 
> If so, one option would be to either modify the stat command or add a
> similar command in debugfs to show the extents from the roots through
> the root down to the leafs. Anyone have preferences or opinions?

The "filefrag" tool in recent e2fsprogs should provide such information,
using the FIEMAP ioctl to extract extent information from the kernel.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.