[PATCH v5 0/6] vhost-user-blk: add compatibility with older qemu versions

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 v5 of the series previously sent as
"[PATCH v4 0/6] vhost-user-blk: fix inflight migration compatibility".

This series extends the vhost-user-blk inflight migration feature
introduced in QEMU 11.0 to address a runtime compatibility problem.

Currently, the inflight migration behaviour in vhost-user-blk is
controlled by VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT, which is
negotiated once at connection time. Once the feature is 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 without reconnecting. This makes it impossible to disable
inflight-migration at runtime, which is needed when, for example,
migrating a VM to an older QEMU version that does not support the
feature.

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 is
semantically identical to GET_VRING_BASE but explicitly 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 operation, GET_VRING_BASE_SKIP_DRAIN during live migration.

In vhost-user-blk, GET_VRING_BASE_SKIP_DRAIN is sent only when
inflight-migration is enabled and the device is stopping due to live
migration (RUN_STATE_FINISH_MIGRATE). The inflight-migration property
is also made mutable so it can be toggled via qom-set at runtime without
reconnecting to the back-end.

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
  vhost-user-blk: move inflight_needed higher
  vhost-user-blk: use GET_VRING_BASE_SKIP_DRAIN during inflight
    migration

 backends/cryptodev-vhost.c        |  2 +-
 backends/vhost-user.c             |  2 +-
 docs/interop/vhost-user.rst       | 88 +++++++++++++++++++------------
 hw/block/vhost-user-blk.c         | 43 ++++++++++++---
 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, 172 insertions(+), 75 deletions(-)

-- 
2.34.1