Re: [PATCH 7/8] qemu: add dbus-vmstate helper migration support

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

On 1/14/20 2:46 PM, marcandre.lureau@xxxxxxxxxx wrote:
> From: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
>
> Helper processes may have their state migrated with QEMU data stream
> thanks to the QEMU "dbus-vmstate".
>
> libvirt maintains the list of helpers to be migrated. The
> "dbus-vmstate" is added when required, and given the list of helper
> Ids that must be migrated, on save & load sides.
>
> See also:
> https://git.qemu.org/?p=qemu.git;a=blob;f=docs/interop/dbus-vmstate.rst
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
> ---
>   src/qemu/qemu_alias.c        |  7 +++
>   src/qemu/qemu_alias.h        |  2 +
>   src/qemu/qemu_command.c      | 62 +++++++++++++++++++++++++++
>   src/qemu/qemu_command.h      |  3 ++
>   src/qemu/qemu_dbus.c         | 14 ++++++
>   src/qemu/qemu_dbus.h         |  4 ++
>   src/qemu/qemu_domain.c       | 10 +++++
>   src/qemu/qemu_domain.h       |  5 +++
>   src/qemu/qemu_hotplug.c      | 82 ++++++++++++++++++++++++++++++++++++
>   src/qemu/qemu_hotplug.h      |  8 ++++
>   src/qemu/qemu_migration.c    | 51 ++++++++++++++++++++++
>   src/qemu/qemu_monitor.c      | 21 +++++++++
>   src/qemu/qemu_monitor.h      |  3 ++
>   src/qemu/qemu_monitor_json.c | 15 +++++++
>   src/qemu/qemu_monitor_json.h |  5 +++
>   15 files changed, 292 insertions(+)


> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index 71d0bb0879..8c281f3a70 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -1125,10 +1125,18 @@ qemuMigrationSrcIsAllowed(virQEMUDriverPtr driver,
>                             bool remote,
>                             unsigned int flags)
>   {
> +    qemuDomainObjPrivatePtr priv = vm->privateData;
>       int nsnapshots;
>       int pauseReason;
>       size_t i;
>   
> +    if (virStringListLength((const char **)priv->dbusVMStateIds) &&
> +        !virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_DBUS_VMSTATE)) {
> +        virReportError(VIR_ERR_OPERATION_INVALID, "%s",
> +                       _("cannot migrate this domain without dbus-vmstate support"));
> +        return false;
> +    }
> +

This should be done in the if(!OFFLINE) a few lines below. IIUC, vmstate 
is runtime thing, and when doing offline migration (e.g. just copying 
over disks and XMLs), no qemu is involved and thus no vmstate matters.

>       /* perform these checks only when migrating to remote hosts */
>       if (remote) {
>           nsnapshots = virDomainSnapshotObjListNum(vm->snapshots, NULL, 0);

Michal