Hi!
On 10/21/25 23:54, Raphael Norwitz wrote:
The logic looks ok from the vhost-user-blk side but some comments inline.
On Mon, Oct 20, 2025 at 1:47 AM Alexandr Moshkov
<[email protected]> wrote:
Hi!
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.
At first, I tried to implement migration for all vhost-user devices that
support inflight at once,
but this would require a lot of changes both in vhost-user-blk (to transfer it
to the base class) and
in the vhost-user-base base class (inflight implementation and remodeling + a
large refactor).
Even if it's a more significant change I'd rather generalize as much
logic as possible and expose it as a vhost-user protocol feature. IMO
too much vhost-user device-agnositic code is being pushed into
vhost-user-blk.
As far as I understand (correct me if I'm wrong), but this feature must
be implemented in device itself (along with inflight field location) or
in some base class for vhost-user devices. For now vhost-user-blkdoesn't
have one yet.The closest base class that i could find is
vhost-user-base, but for using it, it has to implement all
device-agnostic code from vhost-user-blk, and don't break all existing
vhost-user-base derived devices. For example, to support inflight
migration in base class, there first need to implement inflight field in
it, along with the reconnect feature. Then, with a big refactor, somehow
inherit vhost-user-blk from it, along with other devices such as
vhost-user-fs.
So, IMO it looks like a whole separate track that will need to be tackled.
As Markus noted this also conflicts significantly with Vladimir's
series so I'd suggest waiting until those are in, or possibly
attempting to generalize on top of his changes.
Yea, but i think, i just need to perform inflight migration only when
some non-local migration flag is set.
And i think, Vladimir's series already have that flag.
Thanks for the comments!
