On Tue, Jun 10, 2025 at 05:55:31PM -0300, Fabiano Rosas wrote:
> I think I caused some confusion here. I wrote migrate_params_override()
> last thing on a friday and forgot it did the right thing from the
> beginning:
>
> migrate_params_apply(&s->defaults);
> qmp_migrate_set_parameters(new, errp);
>
> This s->defaults is poorly named and is actualy already the merge of
> defaults + globals, because qdev does it for us. migrate_params_apply()
Ha! I didn't remember this part of details when reading, but then I
followed with that idea it won't apply to &defaults.
> will then copy that to s->parameters and qmp_migrate_set_parameters()
> will apply the 'new' params from 'config' on top s->parameters. An
> example:
>
> Setting multifd-channels (default 2) using various methods and querying
> both QMP and HMP:
>
> a) global overrides default:
>
> $ ./qemu-system-x86_64 -global migration.multifd-channels=4 ...
> => QMP: "multifd-channels": 4, HMP: multifd-channels: 4
>
> b) migrate-set-parameter overrides global:
>
> { 'execute': 'migrate-set-parameters', 'arguments': { 'multifd-channels': 8
> } }
> => QMP: "multifd-channels": 8, HMP: multifd-channels: 8
>
> c) config not touching the parameter, value is reset to global:
>
> { 'execute': 'migrate', 'arguments': { ..., 'config': { 'multifd': true } } }
> => QMP: "multifd-channels": 4, HMP: multifd-channels: 4
>
> d) config overrides all:
>
> { 'execute': 'migrate', 'arguments': { ..., 'config': {'multifd-channels':
> 16 } } }
> => QMP: "multifd-channels": 16, HMP: multifd-channels: 16
>
> Without global:
>
> e) default is set initially
>
> $ ./qemu-system-x86_64 ...
> => QMP: "multifd-channels": 2, HMP: multifd-channels: 2
>
> f) migrate-set-parameter overrides default:
>
> { 'execute': 'migrate-set-parameters', 'arguments': { 'multifd-channels': 8
> } }
> => QMP: "multifd-channels": 8, HMP: multifd-channels: 8
>
> g) config not touching the parameter, value is reset to default:
>
> { 'execute': 'migrate', 'arguments': { ..., 'config': { 'multifd': true } } }
> => "multifd-channels": 2, HMP: multifd-channels: 2
>
> h) config overrides all:
>
> { 'execute': 'migrate', 'arguments': { ..., 'config': {'multifd-channels':
> 16 } } }
> => QMP: "multifd-channels": 16, HMP: multifd-channels: 16
>
> I'll update the variable names and code comments to be more
> precise. Sorry for the noise.
Good to know it's even working. Thanks for digging it.
--
Peter Xu
