From 9fda6ab1d9f33c04f35438bce101427dd557fef6 Mon Sep 17 00:00:00 2001 From: "Richard W.M. Jones" Date: Mon, 21 May 2012 14:58:05 +0100 Subject: qemu-img: Explain how rebase operation can be used to perform a 'diff' operation. Signed-off-by: Richard W.M. Jones Signed-off-by: Kevin Wolf --- qemu-img.texi | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'qemu-img.texi') diff --git a/qemu-img.texi b/qemu-img.texi index b2ca3a542c..6fc3c28e0d 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: + +@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} Change the disk image as if it had been created with @var{size}. -- cgit v1.2.1