Re: [PATCH v6 0/6] vhost-user-blk: allow toggling inflight-migration at runtime

Greetings! Ping.

On 8/3/26 12:28, Alexandr Moshkov wrote:
> v5 -> v6:
> - block changing inflight-migration property while VM is not running
> - remove checking runstate in vhost_user_blk_stop() since it's not necessary
> - updated cover letter: changed subject and description to focus on
>    runtime toggling of inflight-migration rather than cross-version
>    migration compatibility
>
> v4 -> v5:
> - introduce protocol feature VHOST_USER_PROTOCOL_F_GET_VRING_BASE_SKIP_DRAIN
>    to guard the new message, instead of reusing the existing
>    VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INLIFGHT. Update docs.
> - improved commit messages.
>
> v3 -> v4:
> - add new protocol message GET_VRING_BASE_SKIP_DRAIN instead of parameter to GET_VRING_BASE message. This new message can be send instead of GET_VRING_BASE, allowing back-end to suspend inflight I/O immediately instead of waiting and completing them.
> - rebase to newer master
>
> v2 -> v3:
> - fix complile problems
> - add assert check in do_vhost_virtio_stop
> - make inflight-migration property mutable
>
> v1 -> v2:
> - reorganize commits: make refactor commits first, then core semantic change
> - add additional pre_save check for inflight migration possibility
>
> ---
>
> This is v6 of the series previously sent as:
> "[PATCH v5 0/6] vhost-user-blk: add compatibility with older qemu versions"
>
> This series allows the inflight-migration property of vhost-user-blk to
> be toggled at runtime via qom-set without restarting the VM or
> reconnecting to the back-end.
>
> Currently, the inflight migration behaviour is controlled by
> VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT, which is negotiated once
> at connection time. Once negotiated, the back-end always uses suspend
> semantics on GET_VRING_BASE -- there is no way for the front-end to
> request normal drain behaviour on a per-call basis. This makes it
> impossible to disable inflight-migration at runtime.
>
> To solve this, the series introduces a new protocol message
> VHOST_USER_GET_VRING_BASE_SKIP_DRAIN (id=45) guarded by a new protocol
> feature VHOST_USER_PROTOCOL_F_GET_VRING_BASE_SKIP_DRAIN. The message
> instructs the back-end to suspend in-flight I/O immediately rather than
> draining it. This gives the front-end explicit per-call control:
> GET_VRING_BASE for normal drain, GET_VRING_BASE_SKIP_DRAIN when
> inflight-migration is enabled.
>
> In vhost-user-blk, GET_VRING_BASE_SKIP_DRAIN is sent whenever
> inflight-migration is on. The inflight-migration
> property can only be changed while the VM is running, so its value at
> stop time reliably reflects the user's intent.
>
> Alexandr Moshkov (6):
>    vhost-user: add skip_drain param to do_vhost_virtqueue_stop
>    vhost-user: add GET_VRING_BASE_SKIP_DRAIN message
>    vhost-user: use skip_drain with GET_VRING_BASE_SKIP_DRAIN message
>    vhost-user-blk: make inflight-migration prop mutable on running vm
>    vhost-user-blk: move inflight_needed higher
>    vhost-user-blk: use GET_VRING_BASE_SKIP_DRAIN when inflight-migration
>      is on
>
>   backends/cryptodev-vhost.c        |  2 +-
>   backends/vhost-user.c             |  2 +-
>   docs/interop/vhost-user.rst       | 88 +++++++++++++++++++------------
>   hw/block/vhost-user-blk.c         | 60 ++++++++++++++++++---
>   hw/net/vhost_net.c                |  9 ++--
>   hw/scsi/vhost-scsi-common.c       |  2 +-
>   hw/virtio/vdpa-dev.c              |  2 +-
>   hw/virtio/vhost-user-base.c       |  2 +-
>   hw/virtio/vhost-user-fs.c         |  2 +-
>   hw/virtio/vhost-user-scmi.c       |  2 +-
>   hw/virtio/vhost-user.c            | 47 ++++++++++++++---
>   hw/virtio/vhost-vsock-common.c    |  2 +-
>   hw/virtio/vhost.c                 | 34 ++++++++----
>   include/hw/virtio/vhost-backend.h |  1 +
>   include/hw/virtio/vhost-user.h    |  2 +-
>   include/hw/virtio/vhost.h         |  7 ++-
>   16 files changed, 189 insertions(+), 75 deletions(-)
>