A couple of comments but overall looks good to me.
On Wed, Oct 29, 2025 at 5:43 AM Alexandr Moshkov
<[email protected]> wrote:
>
> During inter-host migration, waiting for disk requests to be drained
> in the vhost-user backend can incur significant downtime.
>
> This can be avoided if QEMU migrates the inflight region in
> vhost-user-blk.
> Thus, during the qemu migration, the vhost-user backend can cancel all
> inflight requests and
> then, after migration, they will be executed on another host.
>
> In vhost_user_blk_stop() on incoming inter-host migration make force_stop =
> true,
> so GET_VRING_BASE will not be executed.
>
> Signed-off-by: Alexandr Moshkov <[email protected]>
> ---
> hw/block/vhost-user-blk.c | 30 ++++++++++++++++++++++++++++++
> include/hw/virtio/vhost-user-blk.h | 1 +
> 2 files changed, 31 insertions(+)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index a8fd90480a..29d4505d24 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -242,6 +242,12 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
> force_stop = s->skip_get_vring_base_on_force_shutdown &&
> qemu_force_shutdown_requested();
>
Why not move the vhost_user_blk_inflight_needed() helper up here
instead and rather do:
if (vhost_user_blk_inflight_needed(s) &&
runstate_check(RUN_STATE_FINISH_MIGRATE))
As is it looks like vhost_user_blk_inflight_needed() is unused.
> + if (s->enable_inflight_region_migration &&
> + !migrate_local_vhost_user_blk() &&
> + runstate_check(RUN_STATE_FINISH_MIGRATE)) {
> + force_stop = true;
> + }
> +
> s->dev.backend_transfer = s->dev.backend_transfer ||
> (runstate_check(RUN_STATE_FINISH_MIGRATE) &&
> migrate_local_vhost_user_blk());
> @@ -656,6 +662,24 @@ static struct vhost_dev
> *vhost_user_blk_get_vhost(VirtIODevice *vdev)
> return &s->dev;
> }
>
> +static bool vhost_user_blk_inflight_needed(void *opaque)
> +{
> + struct VHostUserBlk *s = opaque;
> +
> + return s->enable_inflight_region_migration &&
> + !migrate_local_vhost_user_blk();
> +}
> +
> +static const VMStateDescription vmstate_vhost_user_blk_inflight = {
> + .name = "vhost-user-blk/inflight",
> + .version_id = 1,
> + .needed = vhost_user_blk_inflight_needed,
> + .fields = (const VMStateField[]) {
> + VMSTATE_VHOST_INFLIGHT_REGION(inflight, VHostUserBlk),
> + VMSTATE_END_OF_LIST()
> + },
> +};
> +
> static bool vhost_user_blk_pre_incoming(void *opaque, Error **errp)
> {
> VHostUserBlk *s = VHOST_USER_BLK(opaque);
> @@ -678,6 +702,10 @@ static const VMStateDescription vmstate_vhost_user_blk =
> {
> VMSTATE_VIRTIO_DEVICE,
> VMSTATE_END_OF_LIST()
> },
> + .subsections = (const VMStateDescription * const []) {
> + &vmstate_vhost_user_blk_inflight,
> + NULL
> + }
> };
>
> static bool vhost_user_needed(void *opaque)
> @@ -751,6 +779,8 @@ static const Property vhost_user_blk_properties[] = {
> VIRTIO_BLK_F_WRITE_ZEROES, true),
> DEFINE_PROP_BOOL("skip-get-vring-base-on-force-shutdown", VHostUserBlk,
> skip_get_vring_base_on_force_shutdown, false),
I would prefer the name indicating that the goal of the parameter was
to skip the GET_VRING_BASE like
"skip-get-vring-base-on-force-shutdown".
Maybe rename it something like
"skip-get-vring-base-inflight-migration"/skip_get_viring_base_migrate_inflight?
> + DEFINE_PROP_BOOL("enable-inflight-migration", VHostUserBlk,
> + enable_inflight_region_migration, false),
> };
>
> static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
> diff --git a/include/hw/virtio/vhost-user-blk.h
> b/include/hw/virtio/vhost-user-blk.h
> index b06f55fd6f..1556714296 100644
> --- a/include/hw/virtio/vhost-user-blk.h
> +++ b/include/hw/virtio/vhost-user-blk.h
> @@ -52,6 +52,7 @@ struct VHostUserBlk {
> bool started_vu;
>
> bool skip_get_vring_base_on_force_shutdown;
> + bool enable_inflight_region_migration;
>
> bool incoming_backend;
> };
> --
> 2.34.1
>
>
