[libvirt] [PATCH 4/4] qemu_capabilities: Temporarily disable dbus-vmstate capability

[Ján Tomko]

On Mon, Sep 09, 2019 at 11:23:59AM +0200, Michal Privoznik wrote:
>On 9/6/19 5:55 PM, Ján Tomko wrote:
>>[cc-ing Marc-André]
>>
>>On Fri, Sep 06, 2019 at 04:25:19PM +0200, Michal Privoznik wrote:
>>>The qemu side is not merged in yet, so there is a chance that the
>>>interface will change. Don't detect the capability just yet then.
>>>
>>>Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>>>---
>>>src/qemu/qemu_capabilities.c | 1 -
>>>1 file changed, 1 deletion(-)
>>>
>>>diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>>>index 136999ad0d..7be026ae12 100644
>>>--- a/src/qemu/qemu_capabilities.c
>>>+++ b/src/qemu/qemu_capabilities.c
>>>@@ -1129,7 +1129,6 @@ struct virQEMUCapsStringFlags 
>>>virQEMUCapsObjectTypes[] = {
>>>    { "virtio-serial-pci-non-transitional", 
>>>QEMU_CAPS_VIRTIO_PCI_TRANSITIONAL },
>>>    { "max-x86_64-cpu", QEMU_CAPS_X86_MAX_CPU },
>>>    { "bochs-display", QEMU_CAPS_DEVICE_BOCHS_DISPLAY },
>>>-    { "dbus-vmstate", QEMU_CAPS_DBUS_VMSTATE },
>>>};
>>>
>>>static struct virQEMUCapsStringFlags 
>>>virQEMUCapsDevicePropsVirtioBalloon[] = {
>>
>>If
>>1) dbus-vmstate is required for migration of a domain using a 
>>slirp-helper and
>>2) we enable this automatically for existing XML configs with
>>  <interface type='user'/> if
>>  a) QEMU has QEMU_CAPS_NET_SOCKET_DGRAM
>>  b) the slirp-helper process is installed on the system
>>then we've effectively made their machines unmigratable
>>
>>So if we want to enable it automatically, we should add:
>>c) QEMU has QEMU_CAPS_DBUS_VMSTATE
>>regardless of whether dbus-vmstate gets merged into QEMU until libvirt's
>>next release
>
>So are you saying that we should just temporarily revert 
>QEMU_CAPS_NET_SOCKET_DGRAM detection instead and leave 
>QEMU_CAPS_DBUS_VMSTATE be?

Give that there was a QEMU release which has one but not the other,
I'd say permanently revert QEMU_CAPS_NET_SOCKET_DGRAM - even if
dbus-vmstate gets merged later, there has been a QEMU release for which
we assume one capability and not the other - so libvirt would be
starting unmigratable machines.

As for QEMU_CAPS_DBUS_VMSTATE, we can either revert it temporarily now
or before the libvirt freeze if dbus-vmstate does not get merged by
then.

Jano

>
>Michal
>
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