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Re: [libvirt] [PATCH] qemuDomainSnapshotCreateActiveExternal: Remove memory snapshot on failure less frequently



On Thu, Aug 30, 2018 at 11:22:35 +0200, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1589115
> 
> When creating a memory snapshot the domain is suspended and qemu
> is told to dump memory into the desired file. After that we set a
> flag so that the file is not left behind if a failure occurs at
> some later point (e.g. when creating disk snapshot fails).
> However, the way we currently handle the memory snapshot file is
> way too aggressive. For instance, if resuming domain vCPUs fails
> after all snapshots were done successfully, we still remove the
> memory snapshot (even though we leave disk snapshot be).
> 
> Signed-off-by: Michal Privoznik <mprivozn redhat com>
> ---
>  src/qemu/qemu_driver.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index a0f7c71675..2eae3dd49d 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -15248,6 +15248,7 @@ qemuDomainSnapshotCreateActiveExternal(virQEMUDriverPtr driver,
>          virObjectEventStateQueue(driver->domainEventState, event);
>      }
>  
> +    memory_unlink = false;
>      ret = 0;

This does not make sense. The snapshot metadata is not saved at this
point so this file would be left over and could not be used (once we
implement external snapshot reversion).

The problem is that you can't get rid of the disk images once the
transaction is executed, but you can dispose of the memory image.

The failure points after the disk snapshot is taken are very hard to
roll back.

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