We haven't found another interface beside from a EFI_PROVIDER bbclass to deploy RMC central database onto ESP (FAT FS) on a hdd image in OE. What can be packed into that directory is dictated by bbclass for each EFI bootloader. Of course, only bootloader-specific data is cared. We either find another existing interface or variable or refactor OE's image bbclass to let any SW to deploy bits on ESP. Then the RMC functionality in a bootloader is split from the deployment of a database file.
While this may capture implementation details, the bigger question is what is the proper user interface for this feature. Right now what we have is: EFI_PROVIDER="rmc-systemd-boot" combined with DISTRO_FEATURES += "rmc" which is obviously redundant and seems to assume the existence of an actual bootloader named 'rmc-system-boot'. Whereas what we conceptually have is a vanilla bootloader named 'systemd-boot' that may or may not have rmc support to enable or disable as needed by the client. This would argue for something more like: EFI_PROVIDER="systemd-boot" combined with DISTRO_FEATURES += "rmc" This was actually implemented at one point, but the problem of what happens when the user specifies some other bootloader that doesn't support rmc - in this case the request was to warn the user at least, but this wasn't possible without some modifications to oe-core. Please see the meta-intel mailing list for the complete discussion. It may be that implementing the title of this bug directly may free us for an even better interface, but so far none other than the above has been proposed.
This task depends on a wic plugin which can deploy non-bootloader-specific data to ESP, like a generic EFI wic plugin tracked in 10073
Work on RMC has been discontinued and it is no longer supported.