Re: [Qemu-devel] [PATCH v2 0/6] migration: objectify MigrationState

[Juan Quintela <quintela@redhat.com>]

Markus Armbruster <armbru@redhat.com> wrote:
> Test compile gripes:
>
>     hw/xen/xen-common.c: In function ‘xen_init’:
>     hw/xen/xen-common.c:147:5: warning: implicit declaration of function ‘register_compat_prop’ [-Wimplicit-function-declaration]
>          register_compat_prop("migration", "store-global-state", "off");
>          ^~~~~~~~~~~~~~~~~~~~
>     hw/xen/xen-common.c:147:5: warning: nested extern declaration of ‘register_compat_prop’ [-Wnested-externs]
>
> You might want to install Xen development packages to catch such issues
> earlier.
>
> Test run:
>
>     $ qemu-system-x86_64 -device migration,help
>     migration.skip-section-footer=bool
>     migration.store-global-state=bool
>     migration.only-migratable=bool
>     migration.skip-configuration=bool
>
> What would adding this device do?

Parameters, capabilities, options for migration.

This was what we discussed on irc.  We want to have a way to control
migration features that depend on versions.

So we disable new features for old machine types (normal thing that we
do).  But right now, creating such a new feature requires creating a
couple of functions to set/clear the feature, adding includes on the
destination side, etc.

This was supposed to be a global property (or a qemu_opt, or whatever).
Just something that could be enabled/disabled easily on machine types,
and if possible independently of machine types.  This (for instance)
would allow that store-global-state is disabled by defaulte for
machine-2.9 (I forgot the exact name for the machine type), but I can
enable it by hand.  That is very handy for testing.

So, I think that the question is, how/where can we set that kind of
properties?

At least for me, being able to *also* set migration
capabilities/parameters with this mechanism on the command line would be
very nice, for instance

   -global migration.xbzrle on

or

   -global migration.max-speed 2G

I don't care about what is the exact syntax, or where we hang them,
i.e. a new device, a new list, somewhere that already exist.  That is
what we ask for advice.

Thanks for the review and the suggestions.

Later, Juan.