Using bios-settings-mgr for setting hypervisor network attributes

[Patrick Williams]

On Wed, Sep 16, 2020 at 08:17:01PM +0530, manoj kiran wrote:
> Hi Ed & James,
> 
> Till now IBM was using phosphor-settings infrastructure as back-end and uses Ethernet Schema for Hypervisor computer system(hypervisor_ethernet.hpp) for setting the IP address of hypervisor. And now we are planning to leverage the capabilities of bios-settings-mgr(backend) as well to set the hypervisor attributes.
> do you see any concerns here ?
> Thanks,
> Manoj

These end up being two quite different implementations from a dbus
perspective, which could have implications to Redfish and webui users.

With 'settings' there is no generic settings interfacess on dbus; every
setting is required to have some modeled interface.  This is great when
you are exposing some hypervisor setting that the BMC also has for
itself, such as network.  We have a single dbus interface for all
network end-points and it doesn't matter if it is for the BMC or the
Hypervisor.

With 'bios-settings-mgr' there are only generic free-form settings
values, which presently can be either int64 or string[1].  This means
there is no overlap with any similar settings we have on the BMC and
there is no programatic way to ensure the data is of the right type and
named with the right key.  This approach is better when you have large
numbers of attributes for concepts which the BMC doesn't have itself.

My understanding was that the 'bios-settings-mgr' was typically going to be
used for uploading a large blob of configuration values and the external
interfaces would have fairly minimal code related to individual
settings.  My concern with using 'bios-settings-mgr' in general is that
it will end up being very tight coupling between external interfaces
(Redfish / webui) and BIOS implementations.  When you use 'settings',
you can implement much more generic external interface code and likely
limit the coupling, if any, to the PLDM provider.

Net is, if you're expecting to be able to modify hypervisor values
through Redfish or WebUI, I think the best approach is to use
'settings'.

1. https://github.com/openbmc/phosphor-dbus-interfaces/blob/77a742627edde54aec625d7c1a200d9f4832f0ba/xyz/openbmc_project/BIOSConfig/Manager.interface.yaml#L44

-- 
Patrick Williams
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