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qemu-img: Explain how rebase operation can be used to perform a 'diff' operation.

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Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Richard W.M. Jones 2012-05-21 14:58:05 +01:00 committed by Kevin Wolf
parent b6c147622d
commit 9fda6ab1d9
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qemu-img.texi
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@ -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. fix an image whose backing file has already been moved/renamed.
@end table @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:
@example
qemu-img create -f qcow2 -b modified.img diff.qcow2
qemu-img rebase -b base.img diff.qcow2
@end example
At this point, @code{modified.img} can be discarded, since
@code{base.img + diff.qcow2} contains the same information.
@item resize @var{filename} [+ | -]@var{size} @item resize @var{filename} [+ | -]@var{size}
Change the disk image as if it had been created with @var{size}. Change the disk image as if it had been created with @var{size}.