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

[zhanghailiang]

Hi,

Is there any news about this discussion?
Is anyone working on it? ;)

Since the 'hard feature freeze' time is closer, we'd better to fix it in 2.4
before libvirt uses it.

I have sent a RFC patch "[RFC] migration: Re-implement 'migrate-set-parameters' to 
make it easily for extension"
http://patchwork.ozlabs.org/patch/482125/
Which just changes qmp command to
 '{ "execute": "migrate-set-parameters" , "arguments":
     { "compression": { "compress-level": 1 } } }',
Compared with its original way, it seems to be more easy for reading and 
extension, but
it can't address most problems discussed here...

Thanks,
zhanghailiang

On 2015/6/5 17:50, Dr. David Alan Gilbert wrote:
> 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 / address@hidden / Manchester, UK