Re: [PATCH 2/5] migration/postcopy: magic value for postcopy channel

[Fabiano Rosas <farosas@suse.de>]

Prasad Pandit <ppandit@redhat.com> writes:

> On Wed, 6 Nov 2024 at 18:41, Fabiano Rosas <farosas@suse.de> wrote:
>> What we're thinking is having an initial exchange of information between
>> src & dst as soon as migration starts and that would sync the
>> capabilities and parameters between both sides. Which would then be
>> followed by a channel establishment phase that would open each necessary
>> channel (according to caps) in order, removing the current ambiguity.
>>
>
> * Isn't that how it works? IIUC, libvirtd(8) sends migration command
> options to the destination and based on that the destination prepares
> for the multifd and/or postcopy migration. In case of 'Postcopy' the
> source sends 'postcopy advise' to the destination to indicate that
> postcopy might follow at the end of precopy. Also, in the discussion
> above Peter mentioned that libvirtd(8) may exchange list of features
> between source and destination to facilitate QMP clients.
>
> * What is the handshake doing differently? (just trying to understand)

The handshake will be a QEMU-only feature. Libvirt will then only start
the migration on src and QEMU will do the capabilities handling.

>
> Thank you.
> ---
>   - Prasad