Re: [Virtio-fs] [PATCH v3 0/5] vhost-user: Back-end state migration

[Stefan Hajnoczi]

Hi Hanna,
I was thinking about how this could work without SUSPEND/RESUME. What
do you think of the following?

1. The front-end sends VHOST_USER_RESET_DEVICE (or
VHOST_USER_RESET_OWNER, when necessary) when the guest driver resets
the device but not on vhost_dev_start()/vhost_dev_stop().
2. Suspend the device when all virtqueues are stopped via
VHOST_USER_GET_VRING_BASE. Resume the device after at least one
virtqueue is started and enabled.
3. Ignore VHOST_USER_SET_STATUS.

Reset would work. The device would suspend and resume without losing
state. Existing vhost-user backends already behave like this in
practice (they often don't implement RESET_DEVICE).

It's close enough to what you're proposing that it doesn't require
much additional work, but I think it covers the cases.

Two concerns:
1. It's specific to vhost-user and diverges from vDPA.
2. VHOST_USER_SET_STATUS might be needed in the future even though
it's not useful today.

Stefan