From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Glanzmann <thomas@glanzmann.de>
Subject: Re: Data Deduplication with the help of an online filesystem check
Date: Wed, 29 Apr 2009 15:58:04 +0200
Message-ID: <20090429135804.GI22917@cip.informatik.uni-erlangen.de>
References: <20090428201619.GK7217@cip.informatik.uni-erlangen.de> <200904282236.07428.hjclaes@web.de> <20090428205242.GA13112@cip.informatik.uni-erlangen.de> <1240952295.15136.73.camel@think.oraclecorp.com> <20090428211255.GB13112@cip.informatik.uni-erlangen.de> <1240953977.15136.76.camel@think.oraclecorp.com> <20090428221455.GA27794@cip.informatik.uni-erlangen.de> <1240960687.15136.88.camel@think.oraclecorp.com> <20090429120300.GG22917@cip.informatik.uni-erlangen.de> <1241010875.20099.2.camel@think.oraclecorp.com>
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Cc: Heinz-Josef Claes <hjclaes@web.de>,
	Edward Shishkin <edward.shishkin@gmail.com>,
	Tomasz Chmielewski <mangoo@wpkg.org>,
	linux-btrfs@vger.kernel.org
To: Chris Mason <chris.mason@oracle.com>
Return-path: <linux-btrfs-owner@vger.kernel.org>
In-Reply-To: <1241010875.20099.2.camel@think.oraclecorp.com>
List-ID: <linux-btrfs.vger.kernel.org>

Hello Chris,

> But, in your ioctls you want to deal with [file, offset, len], not
> directly with block numbers.  COW means that blocks can move around
> without you knowing, and some of the btrfs internals will COW files in
> order to relocate storage.

> So, what you want is a dedup file (or files) where your DB knows a given
> offset in the file has a given csum.

how do I track if a certain block has already been deduplicated?

So, if I only have file, offset, len and not the block number, is there
a way from userland to tell if two blocks are already point to the same
block?

        Thomas