From: Richard W.M. Jones Date: Mon, 21 May 2012 13:58:05 +0000 (+0100) Subject: qemu-img: Explain how rebase operation can be used to perform a 'diff' operation. X-Git-Tag: v1.1.0-rc4~13^2~8 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=9fda6ab1d9f33c04f35438bce101427dd557fef6;p=qemu.git 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 --- diff --git a/qemu-img.texi b/qemu-img.texi index b2ca3a542..6fc3c28e0 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}.