Ping^2 On 10/20/20 10:44 AM, Eric Blake wrote: > On 9/23/20 4:56 PM, Nir Soffer wrote: >> On Wed, Sep 23, 2020 at 11:38 PM Eric Blake <ebl...@redhat.com> wrote: >>> >>> Missed during merge resolution of commit bc5ee6da71. >>> >>> Signed-off-by: Eric Blake <ebl...@redhat.com> >>> --- >>> docs/tools/qemu-img.rst | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst >>> index c35bd6482203..2b5891b54db7 100644 >>> --- a/docs/tools/qemu-img.rst >>> +++ b/docs/tools/qemu-img.rst >>> @@ -265,6 +265,10 @@ Command description: >>> --force allows some unsafe operations. Currently for -f luks, it allows >>> to >>> erase the last encryption key, and to overwrite an active encryption key. >>> >>> + The set of options that can be amended are dependent on the image >>> + format, but note that amending the backing chain relationship should >>> + instead be performed with ``qemu-img rebase``. >> >> Because of the backing format? > > Sorry for not answering this earlier (and now this serves as a ping for > the patch): > > Consider if you have: > > Base.raw <- Overlay.qcow2 > > and want to rebase it to: > > Base.qcow2 <- Overlay.qcow2 > > where Base.raw and Base.qcow2 contain identical guest-visible content. > The problem at hand is that 'qemu-amend' needs to know what the backing > format is both before the rebase (to know how to properly read the > existing image) and after the rebase (to ensure that future opens of > Overlay.qcow2 still properly read the backing format). But there is no > obvious command-line spelling to specify the difference between the > backing format pre-amend and the backing format post-amend. Maybe we > could add that, but I felt it was easier to just document that instead > of trying to amend the image (which involves multiple steps, and may > require upgrading/downgrading between v2 and v3, which in turn may > affect decisions on efficiency of representing regions of zero) at the > same time as the backing file/format, it's easier to just update the > backing file/format with a stand-alone command. > > I can add that to the commit message, if the patch itself is reasonable. >
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
