vhost-user: questions regarding migration

[Anton Kuchin]

Hi,

I'm implementing migration support in vhost-user backend and have a
couple of questions:

1. How master can be sure that logging was started?

We expect that right after set_fatures command with VHOST_F_LOG_ALL flag
all memory modifications will be tracked in log, but slave can need a
little time to process this command so there is a chance that some
requests can be untracked. Is there a way to ensure all requests are
logged or determine the moment since when tracking starts and master can
start migrating memory?

2. Why do we need separate log_addr for vring and how can it be not
covered by mem table?

As far as I understand slave receives used address in set_vring_addr
command and to map it correctly we do need valid entry in memory table.
So this field looks redundant to me. Am I missing something?

BTW the word "log_guest_addr" is mentioned only once in the document and
in "vring address description" payload it is just called "log",
shouldn't we should change this names to match?

pEpkey.asc
Description: application/pgp-keys