Re: [Qemu-devel] [PATCH 0/17 v3] Localhost migration with side channel for ram

[Paolo Bonzini]

Il 25/11/2013 08:29, Lei Li ha scritto:
> 
> 
> In this case, if the migration would fail just because the misconfiguration
> of device state on destination, in the meantime the outgoing migration has
> no aware of this failure, I think it should add such handling (like 
> synchronize
> of the device state list in incoming side?) to the current migration protocol
> as it is kind of missing... It can not just rely on the resume of source
> guest for such failure... or maybe it should be handled in management
> app to force the configuration right?

It is already handled by libvirt, indeed.

Basically, "-incoming" without "-S" is a broken option because of the
missing handshake at the end of migration.  With "-S" something else
(either a human or a program) can check that everything went well and
choose whether to restart the source or the destination.

>> Postcopy would fix this (assuming the postcopy phase is reliable) by
>> migrating device data before any page flipping occurs.
> 
> Are you suggesting that page flipping should be coupled with the postcopy
> migration for live upgrade of QEMU as your comments in the previous
> version?

In order to make live upgrade reliable, it should.

Paolo