Re: [Qemu-devel] [PATCH v3 0/5] Support for datapath switching during live migration

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 07, 2019 at 05:29:39PM -0500, Venu Busireddy wrote:
> Implement the infrastructure to support datapath switching during live
> migration involving SR-IOV devices.
> 
> 1. This patch is based off on the current VIRTIO_NET_F_STANDBY feature
>    bit and MAC address device pairing.
> 
> 2. This set of events will be consumed by userspace management software
>    to orchestrate all the hot plug and datapath switching activities.
>    This scheme has the least QEMU modifications while allowing userspace
>    software to build its own intelligence to control the whole process
>    of SR-IOV live migration.
> 
> 3. While the hidden device model (viz. coupled device model) is still
>    being explored for automatic hot plugging (QEMU) and automatic datapath
>    switching (host-kernel), this series provides a supplemental set
>    of interfaces if management software wants to drive the SR-IOV live
>    migration on its own. It should not conflict with the hidden device
>    model but just offers simplicity of implementation.
> 
> 
> Si-Wei Liu (2):
>   vfio-pci: Add FAILOVER_PRIMARY_CHANGED event to shorten downtime during failover
>   pci: query command extension to check the bus master enabling status of the failover-primary device
> 
> Sridhar Samudrala (1):
>   virtio_net: Add VIRTIO_NET_F_STANDBY feature bit.
> 
> Venu Busireddy (2):
>   virtio_net: Add support for "Data Path Switching" during Live Migration.
>   virtio_net: Add a query command for FAILOVER_STANDBY_CHANGED event.
> 
> ---
> Changes in v3:
>   Fix issues with coding style in patch 3/5.
> 
> Changes in v2:
>   Added a query command for FAILOVER_STANDBY_CHANGED event.
>   Added a query command for FAILOVER_PRIMARY_CHANGED event.

Hmm it looks like all feedback I sent e.g. here:
https://patchwork.kernel.org/patch/10721571/
got ignored.

To summarize I suggest reworking the series adding a new command along
the lines of (naming is up to you):

query-pci-master - this returns status for a device
		   and enables a *single* event after
		   it changes

and then removing all status data from the event,
just notify about the change and *only once*.
	    

upon event management does query-pci-master
and acts accordingly.




>  hmp.c                          |   5 +++
>  hw/acpi/pcihp.c                |  27 +++++++++++
>  hw/net/virtio-net.c            |  42 +++++++++++++++++
>  hw/pci/pci.c                   |   5 +++
>  hw/vfio/pci.c                  |  60 +++++++++++++++++++++++++
>  hw/vfio/pci.h                  |   1 +
>  include/hw/pci/pci.h           |   1 +
>  include/hw/virtio/virtio-net.h |   1 +
>  include/net/net.h              |   2 +
>  net/net.c                      |  61 +++++++++++++++++++++++++
>  qapi/misc.json                 |   5 ++-
>  qapi/net.json                  | 100 +++++++++++++++++++++++++++++++++++++++++
>  12 files changed, 309 insertions(+), 1 deletion(-)