From 2dd9c257fbc243aa76ee6db0bb8371f9f74fad2d Mon Sep 17 00:00:00 2001
From: Joe Thornber <ejt@redhat.com>
Date: Wed, 28 Mar 2012 18:41:28 +0100
Subject: [PATCH] dm thin: support read only external snapshot origins

Support the use of an external _read only_ device as an origin for a thin
device.

Any read to an unprovisioned area of the thin device will be passed
through to the origin.  Writes trigger allocation of new blocks as
usual.

One possible use case for this would be VM hosts that want to run
guests on thinly-provisioned volumes but have the base image on another
device (possibly shared between many VMs).

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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Reading git-format-patch failed