[Qemu-devel] Adding new migration-parameters - any easier way?

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

Hi,
  Is there any way that we could make it easier to add new migration
parameters? The current way is complicated and error prone;
as far as I can tell, to add a new parameter we need to:

  1) qapi-schema.json
    a) Add to 'MigrationParameter' enum, include comment
    b) Add to migrate-set-parameters
    c) Add to MigrationParameters
  2) Define the 'default' macro at the top of migration.c
  3) Add the initialisation to migrate_get_current to set the default
  4) qmp_migrate_set_parameters:
    a) Add the 'has' and value arguments to qmp_migrate_set_parameters
       *** Make really sure this matches the order in migrate-set-parameters!
    b) Add a bounds check on the value
    c) Set the value in the array if the has_ is true
  5) Fixup migrate_init to preserve the parameter around the init
  6) Add a bool and case entry to hmp_migrate_set_parameter and
    pass to qmp_migrate_set_parameters
       *** Make sure you get the order to qmp_migrate_set_parameters right
  7) Fixup hmp_info_migrate_parameters


The three separate changes needed in the qapi-schema.json seem odd,
and the 'has'/value pairs on qmp_migrate_set_parameters is just a nightmare
because there's nothing to check the ordering, and it's just getting
a silly number of arguments to the function now (I've got 10
parameters in one of my dev worlds, so that function has 21 arguments).

In my ideal world there would be:
   a) One thing to add to qapi-schema.json
   b) qmp_migrate_set_parameters would take an array pointer indexed
      by the enum
   c) A way to define the bounds so that we didn't have to manually
      add the bound checking.
   d) Something where I defined the default value

(I'm fairly sure earlier versions of migrate parameters patches
managed (a) and possibly (b)).

Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK