Re: [PATCH v3 1/1] vhost-user-fs: add migration type property

[Michael S. Tsirkin]

On Tue, Feb 28, 2023 at 04:30:36PM +0200, Anton Kuchin wrote:
> I really don't understand why and what do you want to check on
> destination.

Yes I understand your patch controls source. Let me try to rephrase
why I think it's better on destination.
Here's my understanding
- With vhost-user-fs state lives inside an external daemon.
A- If after load you connect to the same daemon you can get migration mostly
  for free.
B- If you connect to a different daemon then that daemon will need
  to pass information from original one.

Is this a fair summary?

Current solution is to set flag on the source meaning "I have an
orchestration tool that will make sure that either A or B is correct".

However both A and B can only be known when destination is known.
Especially as long as what we are really trying to do is just allow qemu
restarts, Checking the flag on load will thus achive it in a cleaner
way, in that orchestration tool can reasonably keep the flag
clear normally and only set it if restarting qemu locally.


By comparison, with your approach orchestration tool will have
to either always set the flag (risky since then we lose the
extra check that we coded) or keep it clear and set before migration
(complex).

I hope I explained what and why I want to check.

I am far from a vhost-user-fs expert so maybe I am wrong but
I wanted to make sure I got the point across even if other
disagree.

-- 
MST