[PATCH v4 03/11] qemu: snapshot: Introduce helpers for creating overlays on <transient/> disks

[Eric Blake]

On 9/24/20 6:43 AM, Peter Krempa wrote:
> To implement <transient/> disks we'll need to install an overlay on top
> of the original disk image which will be discarded after the VM is
> turned off. This was initially implemented by qemu but libvirt never
> picked up this option. With blockdev the qemu feature became unsupported

You may want to add mention that qemu's -transient command-line option 
lets qemu create the file, which fails under various SELinux scenarios 
(as one of the reasons why libvirt never used it).

> so we need to do this via the snapshot code anyways.
> 
> The helpers introduced in this patch prepare a fake snapshot disk
> definition for a disk which is configured as <transient/> and use it to
> create a snapshot (without actually modifying metada or persistent def).

metadata

> 
> Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> ---
>   src/qemu/qemu_snapshot.c | 91 +++++++++++++++++++++++++++++++++++++++-
>   src/qemu/qemu_snapshot.h |  5 +++
>   2 files changed, 95 insertions(+), 1 deletion(-)
> 
-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org