[Qemu-devel] [PATCH 02/10] qemu-img: Explain how rebase operation can be used to perform a 'diff' operation.

[Kevin Wolf]

From: "Richard W.M. Jones" <address@hidden>

Signed-off-by: Richard W.M. Jones <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
---
 qemu-img.texi |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/qemu-img.texi b/qemu-img.texi
index b2ca3a5..6fc3c28 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -159,6 +159,24 @@ It can be used without an accessible old backing file, 
i.e. you can use it to
 fix an image whose backing file has already been moved/renamed.
 @end table
 
+You can use @code{rebase} to perform a ``diff'' operation on two
+disk images.  This can be useful when you have copied or cloned
+a guest, and you want to get back to a thin image on top of a
+template or base image.
+
+Say that @code{base.img} has been cloned as @code{modified.img} by
+copying it, and that the @code{modified.img} guest has run so there
+are now some changes compared to @code{base.img}.  To construct a thin
+image called @code{diff.qcow2} that contains just the differences, do:
+
address@hidden
+qemu-img create -f qcow2 -b modified.img diff.qcow2
+qemu-img rebase -b base.img diff.qcow2
address@hidden example
+
+At this point, @code{modified.img} can be discarded, since
address@hidden + diff.qcow2} contains the same information.
+
 @item resize @var{filename} [+ | address@hidden
 
 Change the disk image as if it had been created with @var{size}.
-- 
1.7.6.5